Whispers from the Dark Universe - Particles & Fields in the Gravitational Wave Era

24 Sept 2024, 12:00 → 27 Sept 2024, 21:00 Europe/Berlin

Main Auditorium (DESY Hamburg)

The annual DESY Theory Workshop is organized by the elementary particle physics community in Germany. The focus is on a topical subject in theoretical particle physics and related fields. More details can be found on the conference homepage.

The workshop features:

• plenary sessions of specialized talks by invited speakers.
• parallel sessions, allowing young researchers to present their work ( Wednesday and Thursday afternoon ).
• The DESY Heinrich-Hertz-Lecture on Physics for public outreach.

 

 

2024-Theorie-Workshop-Poster-WEB_30Jul2024.pdf

Poster Hertz Lecture_2024.pdf

Tuesday 24 September

Registration

Welcome

desy-intro.pdf

Plenary Sessions Tuesday I

Convener: Prof. Cora Uhlemann (Bielefeld University)

1 Inflation

Speaker: M. Peloso (Padova U.)

desy24-peloso.pdf

2 CMB

Speaker: R. Flauger

Flauger.pdf

3 WISPs / structure

Speaker: C. Prescod-Weinstein

Prescod-Weinstein-DESY.pdf

16:00 Coffee break

Plenary Sessions Tuesday II

Convener: Pedro Schwaller (University of Mainz)

4 Early Universe GWs

Speaker: X. Siemens

5 Phase Transitions

Speaker: J. van de Vis

PTsJvdVis.pdf

6 Pulsar Timing Arrays

Speaker: N. Porayko

PTA_DESY.pdf

18:30 Reception

Wednesday 25 September

Plenary Sessions Wednesday I

Convener: Felix Kling (T (Cosmology))

7 Light Relics, Freeze-in, and Dark Photons

Speaker: K. Schutz

DESY2024.pdf

8 Precision Calc. for DM

Speaker: J. Harz

DESY2024_TheoryWorkshop-1.pdf

9 Axion Theory

Speaker: P. Agrawal

DESY-Sep2024.pdf

11:00 Coffee break & workshop photo

Plenary Sessions Wednesday II

Convener: Kai Schmitz (University of Münster)

10 Axion Strings

Speaker: M. Buschmann

DESY_2024.pdf

11 Gravitational wave forms for conventional and exotic sources

Speaker: E. Lim

DESY_2024.pdf

12:50 Lunch

Parallel Wednesday Cosmo 1

12 Sommerfeld effect and bound state formation for Dark Matter with colored mediators: a computational framework

In the universal framework of simplified t-channel dark matter models, the relic abundance is dominated by mediator annihilation in most of parameter space, which gets considerably enhanced by the Sommerfeld effect and bound state formation. We provide an intuitive and easy to use add-on package to micrOMEGAs, allowing for an automated inclusion of these effects for a generic t-channel dark matter model. Albeit their effect is subdominant in the coannihilation regime, excited bound state levels are included as well. We analyze representative models with scalar and fermionic mediators and highlight the differences and common features between the two.

Speaker: Martin Napetschnig (Technical University of Munich)

Napetschnig_tchannel_BSF.pdf

13 Cosmic Birefringence by Dark Photon

We study the kinetic mixing between the cosmic microwave background (CMB) photon and the birefringent dark photon. These birefringent dark photon may exist in parity-violating dark sector, for example, through the coupling to axion field. We show that the birefringence of the dark photon propagates to the CMB photon, but the resulting birefringence may not be isotropic over the sky, but will be anisotropic in general. Moreover, our investigation sheds light on the essential role played by kinetic mixing in the generation of two fundamental characteristics of the CMB: circular polarization and spectral distortion.

Speaker: Sung Mook Lee (KAIST)

DESY_SMLEE.pdf

14 Signatures of ultralight bosons in the orbital eccentricity of binary black holes

It is well known that clouds of ultralight particles surrounding black holes produced by the superradiant instability can experience Landau-Zehner transitions if the black hole is part of a binary system.
We study the effect of orbital eccentricity, backreaction of the cloud onto it and observational possibilities with future gravitational-wave detectors like the Laser Interferometer Space Antenna, as well as the planned deciHertz gravitational-wave observatories. For black hole binaries with chirp masses below $10\,M_\odot$ , such effects would provide strong evidence for the existence of a new particle of mass between $10^{-13}$ to $10^{-11}\,\mathrm{eV}$.

Speaker: Dr Mateja Boskovic (DESY)

M_Boskovic_SR_desy_th.pdf

15 Populating sequestered dark sector with ultra-relativistic bubbles

We study Dark Matter production during first order phase transitions from bubble-plasma collisions. We focus on scenarios where the Dark Matter sector is secluded and its interaction with the visible sector (including the Standard Model) originates from dimension-five and dimension-six operators. We find that such DM is generally heavy and has a large initial velocity, leading to the possibility of DM being warm today. We differentiate between the cases of weakly and strongly coupled dark sectors, where, in the latter case, we focus on glueball DM, which turns out to have very distinct phenomenological properties. We also systematically compute the Freeze-In production of the dark sector and compare it with the bubble-plasma DM abundances.

Speaker: Miguel Vanvlasselaer (VUB)

Presentation (82).pdf

16 Whispers from the dark universe about weak lensing one-point statistics

Weak lensing offers a way to directly probe the matter distribution that is sensitive to the physics of the dark universe, in particular dark matter and dark energy. Since weak lensing is a projected effect, it is not possible to fully recover the time evolution of the density field. Tomography is crucial to recover this evolution for disentangling physical effects. The one-point probability distribution function (PDF) carries additional information about density environments compared to standard two-point statistics. At intermediate scales, the large deviation theory accurately predicts the convergence PDF and its changes with cosmological parameters at different redshifts. Additionally, the theoretical model for the convergence PDF can be adapted to include weak lensing systematics. This work investigates the constraining power of the tomographic convergence PDF using these predictions. We cross-validate predicted and measured convergence PDFs derived from convergence maps reconstructed with shear catalogues from an N-body simulation. Fisher forecasts show enhanced constraints with tomography compared to non-tomography and shear two-point correlation functions. This is due to the additional information provided by the skewness at different redshift bins. The tomographic convergence PDF can track structure growth and capture non-Gaussian information across scales, demonstrating strong potential for constraining cosmological parameters.

Speaker: Lina Castiblanco (Newcastle University)

Lina_Castiblanco.pdf

17 Ultra-high Frequency Gravitational Waves from Scattering, Bremsstrahlung and Decay during Reheating

Gravitational waves (GWs) present a promising avenue to probe the physics of inflationary reheating, which may play a crucial role in the thermal history of the early Universe. In this talk, I will discuss the unavoidable sources of GWs from graviton production during reheating. The processes under consideration include: $(i)$ $1 \to 3$ graviton Bremsstrahlung, $(ii)$ $2 \to 2$ scattering of the inflaton and its decay products, $(iii)$ pure inflaton $2 \to 2$ scattering, and $(iv)$ one-loop induced inflaton decay. Through a comprehensive comparison of these four sources of GWs, we will identify the conditions under which the dominant source emerges. Finally, I will comment on how future high-frequency detectors could potentially reveal the dynamics of reheating.

Speaker: Yong Xu (MITP, JGU Mainz)

DESY_XU.pdf

18 Gravitational wave spectrum from expanding string loop on domain wall

It is well known that spontaneous breaking of discrete symmetries produce topological objects called domain walls, which must decay in order not to dominate the energy density of the universe. One of the possible decay scenarios is nucleating holes bounded by cosmic strings on the walls. Once they are nucleated, the holes expand faster and faster by eating the energy of the domain walls and may radiate stochastic gravitational waves with significant energy fraction. This resembles cases of bubble collisions in cosmological 1st-order phase transition. We derive an analytic expression for the GW spectrum radiated from these string loops expanding on the walls. Remarkably, the spectrum is found to be proportional to frequency in UV region, in contrast to usual bubble collisions. We also discuss the implication to the NANOGrav signal and future GW observatories.

Speaker: Dr Yu Hamada (T (Cosmo))

DESYTH_hamada.pdf

19 Induced Domain Walls of QCD Axion, and Gravitational Waves

We show that heavy axion domain walls induce domain walls of the QCD axion through a mixing between the heavy axion and the QCD axion, even when the pre-inflationary initial condition is assumed for the QCD axion. The induced domain walls arise because the effective $\theta$ parameter changes across heavy axion domain walls, shifting the potential minimum of the QCD axion. When the heavy axion domain walls collapse, the induced QCD axion domain walls collapse as well. This novel mechanism for producing the QCD axions can explain dark matter even with the axion decay constant as small as ${\cal O}(10^{9-10})$ GeV. In particular, this scenario requires domain wall collapse near the QCD crossover, potentially accounting for the stochastic gravitational wave background suggested by recent pulsar timing array observations, including NANOGrav.

Speaker: Kai Murai (Tohoku University)

InducedDW_Murai.pdf

16:09 Coffee break

20 Gravitational Waves from Low-Scale Cosmic Strings

In this talk, I will discuss the effect of low cosmic string tensions on the associated stochastic gravitational wave background. I will show that the gravitational wave spectrum is qualitatively different from the one produced by cosmic strings with larger tensions. In fact, it exhibits a very distinct oscillatory feature with dips in the amplitude at multiples of the frequency of the first dip. This feature arises if none of the cosmic string loops chopped off from the long-string network have fully decayed yet. Despite the low tensions, such an SGWB would be measurable in future experiments.

Speaker: Tobias Schroeder (University of Münster)

Talk_String_Oscillations_12min-6.pdf

21 Ultrahigh frequency GW backgrounds from cosmic strings

This talk focuses on gravitational-wave backgrounds (GWB) from cosmic strings that would manifest only at ultra-high frequencies (above kilohertz), that leave no signal at either LIGO, Einstein Telescope, or LISA, and correspond to high-energy scale (beyond $10^{10}$ GeV) particle physics parameters. Signals from metastable local strings, with amplitude as large as the $\Delta N_{\rm eff}$ bounds, offer exciting prospects to probe grand unification physics. Beyond the information of the symmetry-breaking scale, the high-frequency spectrum encodes the microscopic structure of the strings through the position of the UV cutoff. The detection of such cut-off enables the reconstruction of the scalar potential, particularly the scalar self-coupling. We estimate the needed reach of hypothetical futuristic GW detectors to probe such GW and, therefore, the corresponding high-energy physics processes. On the other hand, the GWB from global axionic strings is suppressed even for large symmetry-breaking scales due to the matter era from the associated heavy axions. (Based on Phys. Rev. D 109, 103538 [arXiv:2312.09281])

Speaker: Peera Simakachorn (IFIC, Valencia U.)

DESY2024_Peera.pdf

22 Gravitational waves from domain wall collapse, and application to nanohertz signals with QCD-coupled axions

We study for the first time the gravitational waves generated during the collapse of domain walls, incorporating the potential bias in the lattice simulations. The final stages of domain wall collapse are crucial for the production of gravitational waves but have remained unexplored due to computational difficulties. As a significant application of this new result, we show that the observed NANOGrav, EPTA, PPTA, and CPTA data, which indicate stochastic gravitational waves in the nanohertz regime, can be attributed to axion domain walls coupled to QCD. In our model, non-perturbative effects of QCD induce a temperature-dependent bias around the QCD crossover, inducing the rapid collapse of the domain walls. We use sophisticated lattice simulations that account for the temperature-dependent bias to measure the gravitational waves resulting from the domain wall annihilation. We also discuss the future prospects for accelerator-based searches for the axion and the potential for the formation and detection of primordial black holes.

Speaker: Junseok Lee (Tohoku University)

DESY_24_Lee.pdf

23 Confinement slingshot and gravitational waves

The gauge “slingshot” effect occurs when a source, such as a quark or a magnetic monopole, crosses the boundary between the Coulomb and confining phases during a first-order phase transition. The corresponding gauge field of the source, either electric or magnetic, gets confined into a flux tube stretching in the form of a string (cosmic or a QCD type) that attaches the source to the domain wall, separating the two phases. The string tension accelerates the source toward the wall as a slingshot. Various sources of other dimensionality also exhibit the slingshot phenomenon, such as cosmic strings confined by domain walls or vortices confined by $𝑍_2$ strings. Apart from the field-theoretic value, the slingshot effect has important cosmological implications, as it provides a distinct source for gravitational waves. The effect is expected to be generic in various standard model extensions, such as grand unification.

Speaker: Juan Sebastian Valbuena Bermudez (IFAE, Autònomous University of Barcelona)

Confinement Slingshot and Gravitational Waves

Confinement slingshot and gravitational waves .pptx

24 Fine-tuning of the Higgs parameter in the thermal evolution of the universe

The electroweak hierarchy problem is often a source of controversy – do we need to care about the Higgs curvature parameter $\mu^2$ being tuned to a small value, against quantum field theoretical expectation?
We explore the possibility that $\mu^2$ is initially large – as expected when introducing physics beyond the standard model – and is dynamically tuned to its current value at zero temperature, e.g. by the presence of another large vacuum expectation value (vev). Since the Higgs mass parameter then varies over the evolution of the universe, one may run into cases of super high scale electroweak symmetry breaking, yielding a large Higgs vev and thereby very massive SM particles.
Although such a scenario does not solve the hierarchy problem, it could have interesting cosmological impacts, including but not limited to gravitational waves from the transition in the scalar potential and it could give an insight on the nature of the hierarchy problem.
If the system can be kept in a large Higgs vev phase until very late times, this would even lead to a first order QCD deconfinement phase transition, since QCD can be described as a pure gauge theory in the limit of decoupling quarks.

Speaker: Aika Marie Tada (Max-Planck-Institut für Kernphysik)

Fine-tuning of the Higgs parameter in the thermal.pdf

25 Neutrino Oscillations as a Gravitational Wave Detector?

Gravitational Waves (GWs) can alter the neutrino propagation distance and thus affect neutrino oscillations. This can result in a complete disappearance of the oscillatory behavior that competes with other sources of neutrino decoherence. We develop a set of criteria that determines under which conditions neutrino oscillations are sensitive to this effect, and discuss three concrete scenarios for neutrinos from astrophysical sources. We find that neutrino oscillations may probe so far unexplored regions of the GW parameter space.

Speaker: Sara Krieg

talk.pdf

Parallel Wednesday Cosmo 2

26 Hybrid inflation and gravitational waves from accidentally light scalars

We construct a hybrid-inflation model where the inflaton potential is generated radiatively, as gauge symmetries guarantee it to be accidentally flat at tree level. The model can be regarded as a small-field version of Natural Inflation, with inflation ending when the mass of a second scalar, the waterfall field, turns tachyonic. This provides a minimal, robust realisation of hybrid inflation, which predicts specific correlations among CMB observables. Tachyonic preheating leads to the production of gravitational waves which, for a low inflationary scale, might be detected by upcoming experiments. Simple variations of the model can give rise to topological defects, such as unstable domain walls. Their dynamics produces a stochastic gravitational-wave background, which can be compatible with the recent detection by pulsar timing arrays.

Speaker: Giacomo Ferrante (Laboratoire Univers et Particules de Montpellier - CNRS)

Giacomo_Ferrante.pdf

27 PQ inflation at the pole

In this work we extend the Standard Model with a Peccei-Quinn (PQ) scalar, whose radial component drives inflation near the pole of its kinetic term, and identify the angular component with the axion field. During inflation, the PQ violating terms give a non-zero velocity to the axion, which evolves with an approximately conserved Noether PQ charge. We investigate the reheating dynamics and study the production of Dark Matter through the misalignment mechanism.

Speaker: Adriana Menkara (Chung Ang University)

Adriana_DESYTH.pdf

28 Improving the description of Schwinger pair production during axion inflation

Axion inflation is a well-motivated inflationary model with many fascinating phenomenological consequences, for example, the production of large scalar perturbations, which could seed primordial black holes and source scalar-induced gravitational waves. Furthermore, the parity-violating nature of axion inflation implies the production of circularly polarized gravitational waves. The production of gauge fields during axion inflation also allows for a possible study of reheating after inflation.
Importantly, strong electromagnetic fields sourced during axion inflation can also lead to fermion production via the well-known Schwinger effect. This is especially relevant when the inflaton field couples to the U(1)-hypercharge gauge field, which is guaranteed to couple to fermionic charge carriers, i.e., the Standard Model fermions. In our study, we improve upon the current modeling of Schwinger pair production during axion inflation by explicitly accounting for the typical spatial separation of fermion pairs at the time of production. This introduces a new scale in the backreaction of Schwinger pair production which affects the damping of the gauge fields by the conducting medium. Furthermore, we demonstrate how moving away from the typical assumption of collinear hyperelectric and -magnetic fields allows one to simultaneously resolve an ambiguity that previously existed in the literature. This work therefore presents an important step forward towards a complete understanding of gauge-field production during axion inflation.

Speaker: Richard von Eckardstein (Institute for Theoretical Physics, University of Münster)

Fermion_Production_in_Axion_Inflation___DESY_Th_Workshop_2024-1.pdf

29 Inflation and current couplings in the Einstein-Cartan gravity

Einstein–Cartan $f(R)$ theory is known not to induce an additional scalar degree of freedom, the scalaron, contrary to the case in the metric formalism. In this research, we show that by including other geometric quantities in the Einstein-Cartan gravity such as the Nieh-Yan and the Holst term, it is possible to have a propagating scalaron and realize alpha-attractor inflation and its deformation. We also discuss matter currents coupled to the scalaron in this setup.

Speaker: Muzi Hong (The University of Tokyo)

slides_Hong.pdf

30 Revisiting Isocurvature Evolution

While adiabatic perturbations explain CMB and large-scale structure data very well, isocurvature fluctuations could still play a subdominant role. The observation of such a perturbation could hint at more complex cosmic histories such as multi field inflation scenarios. Interactions between the primordial fluids would determine the isocurvature amplitudes in the present epoch.
We revisit the evolution of isocurvature and introduce a novel approach to evaluate it, returning to an easy-to-implement transfer matrix depiction. We show that the approach is equivalent to previous formulations of isocurvature evolution in the separate-universe picture and give examples for cosmic histories with interacting fluids or a curvaton.

Speaker: Christopher Gerlach (Johannes Gutenberg-Universität Mainz)

Isocurvature_DESY_2024_Slides_V1.pdf

31 The Inflationary Butterfly Effect: Non-Perturbative Dynamics From Small-Scale Features

For the first time, we investigate the non-perturbative dynamics of single field inflation with a departure from slow-roll. Using simulations, we find that oscillatory features in the potential can drastically alter the course of inflation, with major phenomenological implications. In certain cases, the entire Universe gets trapped in a forever inflating de Sitter state. In others, only some regions get stuck in a false vacuum, offering an alternative channel for primordial black hole formation. Analogous to the flap of a butterfly, these results show that small-scale phenomena can have profound consequences on the evolution of the entire Universe. This demonstrates the necessity of a non-perturbative approach in the exploration of the small-scale physics of inflation, particularly in the regime relevant for gravitational-wave astronomy. Additionally, we compare our fully nonlinear lattice power spectra with perturbative 1-loop calculations.

Speaker: Angelo Caravano (IAP Paris)

DESY24_Caravano.pdf

32 Non-Gaussian tails without stochastic inflation

The tail of the PDF of primordial scalar perturbations is a key element to determine the abundance of primordial black holes. These primordial non-Gaussianities arise, at least partly, from the non-linear, super-horizon dynamics of inflationary perturbations. Such non-linear evolution is usually addressed through the stochastic $\delta N$ formalism. This formalism is based on the deterministic $\delta N$ formalism, which captures the non-linear relation between curvature and inflaton perturbations, and is then supplemented with the stochastic formalism of inflation, which accounts for the backreaction of quantum fluctuations into large-scale inflaton dynamics. In our work, we reconsider the underlying assumptions and implications of this calculation using both numerical and analytical methods, assessing the validity of several approximations commonly used in the literature.

Speaker: Alejandro Perez Rodriguez (Universidad Autonoma de Madrid)

DESYTW24_Alejandro_Perez_Rodriguez.pdf

33 One-loop power spectrum in USR inflation and implications for PBH DM

A possible way to generate primordial black holes as candidates for the entirety of dark matter is a large power spectrum of inflationary curvature fluctuations. Recently, questions have been raised regarding the validity of perturbation theory in this context. We compute the one-loop power spectrum in ultra-slow roll inflation, including all relevant interactions for such analysis, along with counterterms that absorb the ultraviolet divergences. We compare the one-loop and tree-level contributions to the power spectrum, finding that perturbation theory remains valid in realistic ultra-slow roll models.

Speaker: Jesus Gambin Egea (Instituto de Fisica Teorica, UAM - CSIC)

Jesus_Gambin_Egea.pdf

16:09 Coffee Break

34 Curvature Perturbations Protected Against One Loop

We examine one-loop corrections from small-scale curvature perturbations to the superhorizon-limit ones in single-field inflation models, which have recently caused controversy. We consider the case where the Universe experiences transitions of slow-roll (SR) → intermediate period → SR. The intermediate period can be an ultra-slow-roll period or a resonant amplification period, either of which enhances small-scale curvature perturbations. We assume that the superhorizon curvature perturbations are conserved at least during each of the SR periods. Within this framework, we show that the superhorizon curvature perturbations during the first and the second SR periods coincide at one-loop level in the slow-roll limit.

Speaker: Keisuke Inomata (Johns Hopkins University)

desy_talk_sep_25_inomata.pdf

35 Stochastic Gravitational Waves and Higgs Stability via Non-Minimal Curvature Couplings

A non-minimal interaction between the Standard-Model Higgs and spacetime curvature offers a fascinating connection between the physics of post-inflationary reheating and the parameters of the Standard Model. Such an interaction helps stabilising the Higgs at high energies, avoiding the problem of vacuum stability during inflation. It also leads to the explosive tachyonic production of Higgs particles during a post-inflationary phase of kinetic-energy domination due to a change in sign of the Ricci scalar. In this talk, I will discuss the stochastic gravitational wave background produced in a so-called Hubble-induced phase transition which can be investigated via semi-analytical computations and fully-fledged lattice simulations. By exploring a wide range of model parameters, it is possible to reconnect the characteristics of the gravitational-wave signal to the scale of the phase transition, the strength of the non-minimal interaction and the running of the Higgs self-coupling, thus opening a new window into the Higgs effective potential at high scales.

Speaker: Giorgio Laverda (CENTRA - IST, University of Lisbon)

presentation_DESY_2024.pdf

36 Gravitational waves in ultra-slow-roll and their anisotropy at two loops

We compute the non-Gaussian corrections to the energy density and anisotropies of gravitational waves induced after an ultra-slow-roll phase of inflation by using a diagrammatic approach, and present the corresponding Feynman rules. Our two-loop calculation includes both the intrinsic non-Gaussianity of the inflaton perturbation $\delta\phi$ and the non-Gaussianity arising from the nonlinear relation between the latter and the curvature perturbation $\mathcal{R}$. We apply our formalism to an analytical model in which the ultra-slow-roll phase is followed by a constant-roll stage with a non-vanishing second slow-roll parameter $\eta$, and address the renormalization of the one-loop scalar power spectrum in this scenario.

Speaker: Julian Leonardo Rey Idler (T (Cosmology))

gws-short.pdf

37 Gravitational waves from primordial black hole reheating in a general cosmological background

Although there is substantial observational evidence for an early period of exponential expansion of the Universe, known as inflation, followed by a subsequent era of radiation domination, the intermediate period connecting these two epochs, referred to as reheating, remains challenging to constrain.

In this talk, I will present the primordial black hole (PBH) reheating scenario, where tiny black holes temporarily dominate the Universe and reheat it via Hawking radiation from their evaporation. I will discuss the gravitational wave (GW) spectrum induced by PBH number density fluctuations, paying particular attention to how features of the spectrum depend on the (so far unconstrained) equation of state of the primordial fluid. The GW signal may enter the observational window of several future GW detectors, such as LISA and the Einstein Telescope, indicating that it may soon be possible to directly probe the physics of the earliest moments of the Universe via induced GWs.

Speaker: Jan Tränkle (ITP Leibniz Universität Hannover)

Jan_Traenkle.pdf

38 Enhanced induced gravitational waves in Horndeski gravity

Gravitational waves (GWs) provide a powerful probe to test gravity in the very early Universe. This presentation will explore the effects of a Horndeski scalar field on secondary scalar-induced GWs. The higher-derivative interactions easily dominate the source term on subhorizon scales, significantly enhancing the amplitude of induced GWs. The main effects of these modifications of gravity are stronger resonances and a growth of tensor fluctuations on small scales. The maximum attainable amplitude of the induced GW spectrum is bounded by the potential backreaction of higher derivatives on curvature fluctuations, thereby shutting down the source term to induced GWs. Remarkably, in the case of a scale-invariant primordial curvature power spectrum, the Horndeski-induced GW spectrum grows as $k^3$. This opens up the intriguing possibility that induced GWs might be observable even without an enhancement of the primordial curvature power spectrum.

Speaker: Alexander Ganz

Enhanced Induced GWs in Horndeski Gravity.pdf

39 Probing primordial black hole mergers with PTAs

In this talk, I will discuss how pulsar timing arrays (PTA) can probe primordial black holes (PBH) through gravitational waves. If PBHs exist, they can form in the early universe from the collapse of large density perturbations, necessarily triggering a background of secondary-order scalar-induced gravitational waves. In the late universe, these PBHs will form clusters, leading to enhanced PBH binary merger rates that can also contribute to a gravitational wave background. Additionally, I will discuss the parameter space favored by the latest PTA data release for this model and its physical implications.

Speaker: Sonali Verma (ULB Brussels)

desy_pbh_sverma.pdf

Parallel Wednesday Pheno 1 / Cosmo 3

40 Di-Higgs production in the RxSM at the HL-LHC taking into account 1-loop corrections to the trilinear Higgs couplings in a SFOEWPT scenario

We explore the real-singlet extension of the Standard Model without a Z2 symmetry (RxSM), as a model to reconstruct the Higgs potental and explain the baryon asymmetry of the Universe. First, we determine regions of parameter space that allow a Strong First-Order Electroweak Phase Transition (SFOEWPT) using the public tools CosmoTransitions and TransitionListener, including also relevant theoretical constraints as well as experimental constraints using HiggsTools. Then, we compute the one-loop corrections to the trilinear Higgs couplings that enter di-Higgs production (hhh and hhH) using the public code anyH3. Finally, we compute the di-Higgs production cross section at the (HL-)LHC in the regions of the RxSM parameter space allowing a SFOEWPT, taking into account the one-loop corrections to the trilinear Higgs couplings. We compare this new result with the results in the SM and in the RxSM at tree level, highlighting the impact of the loop corrections to the trilinear couplings.

Speaker: Alain Verduras Schaeidt (T (Phenomenology))

AVS_DESYTheor.pdf

41 CP-sensitive simplified template cross-sections for ttH

The CP structure of the Higgs boson is a fundamental property which has not yet
been constrained with high precision. CP violation in the Yukawa coupling between the
Higgs boson and top quark pair can be probed directly at the Large Hadron Collider
by measuring top-quark-associated Higgs production. Multivariate analysis techniques
commonly developed so far by the experiments are designed for a specific signal model
and, therefore, complicate reinterpretations and statistical combinations. With this
motivation in mind, we propose a CP-sensitive extension of the simplified template
cross-section (STXS) framework. Considering multiple Higgs decay channels, we per-
form an in-depth comparison of CP-sensitive observables and combinations thereof.
Our resulting proposal is to extend the existing binning in the transverse momentum
of the Higgs boson pT,H by either the pseudorapidity difference of the two top-quarks, or a variable that is based on the top quark momenta, namely b2 or the Collins-
Soper angle. We demonstrate that this variable selection provides close to
optimal sensitivity to the CP mixture in the top Yukawa coupling for an integrated
luminosity of 300 fb−1, by comparing it to the results of a multivariate analysis. Our
results also suggest a benefit of the two-dimensional STXS extension at 3000 fb−1.

Speaker: Marco Menen

DESY_Theory_Workshop_24.pdf

42 Impact of Loop Corrections to the Trilinear Higgs Couplings and Interference Effects on Experimental Limits

We investigate the reliability of a comparison between the experimental results and the theoretical predictions for the pair production of the 125 GeV Higgs boson at the LHC. Recent experimental results for di-Higgs production provide already sensitivity to triple Higgs couplings (THCs) in models beyond the Standard Model (BSM). In our analysis within the Two Higgs Doublet Model (2HDM) we find that potentially large higher-order corrections to the trilinear couplings and the interference effects arising from additional heavy states have a strong impact on the expected shape of the differential cross section and the value of the total cross section. Both effects have to be taken into account for a correct interpretation of the experimental results. In particular, we demonstrate that neglecting the interference of the contributions of heavy Higgs resonances with non-resonant (background) diagrams, as done by the experimental collaborations, can lead to unreliable exclusion limits.

Speaker: Kateryna Radchenko Serdula (T (Phenomenology))

TW24_Radchenko.pdf

43 Analysis of interference effects in the di-top final state for CP-mixed scalars in extended Higgs sectors

Various extensions of the Standard Model predict the existence of additional Higgs bosons. If these additional Higgs bosons are sufficiently heavy, an important search channel is the di-top final state. In this channel, interference contributions between the signal and the corresponding QCD background process are expected to be important. If more than one heavy scalar is present, besides the signal-background interference effects associated with each Higgs boson also important signal-signal interference effects are possible. We perform a comprehensive model-independent analysis of the various interference contributions within a simplified model framework considering two heavy scalars that can mix with each other, taking into account large resonance-type effects arising from loop-level mixing between the scalars. The interference effects are studied with Monte Carlo simulations for the di-top production process at the LHC. We demonstrate that signatures can emerge from these searches that may be unexpected or difficult to interpret.

Speaker: Romal Kumar (T (Phenomenology))

20240925_romal_desy_workshop.pdf

44 Vacuum (in)stability in N2HDM vs 2HDMS

(Meta)stability of the EW vacuum is a crucial requirement for models with extended scalar sectors, which puts strong constraints on the parameter space of such models. In this work, we compare the vacuum structure of two extended scalar models, namely N2HDM (2HDM+real singlet) and 2HDMS (2HDM+complex singlet) and the intrinsic difference between them. We further investigate whether such differences persist, once the experimental constraints are imposed on both models. Lastly, we motivate the measurement of tri-linear Higgs coupling in this context, which can help us probe the different vacuum structures in the two models.

Speaker: Jayita Lahiri (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

talk_JayitaLahiri_DESY.pdf

45 Radiative corrections to $B\rightarrow \ell \nu$

In this talk I will focus on the study of the leptonic $B^-\rightarrow\ell^- \bar{\nu}_\ell$
at next-to-leading order in QED. The future improvements of experimental measurements of this channel require a reliable theory prediction, hence a careful theoretical estimate of QED corrections. The multi-scale character of this process requires an appropriate effective theory (EFT) construction to factorize the different contributions. In the first part of this talk, I will discuss the EFT description of the process at the partonic level, which is based on Heavy Quark Effective Theory and Soft Collinear Effective Theory. I will show how the inclusion of QED corrections demands a generalisation of the hadronic decay constant . In the second part of the talk, I will discuss the EFT description below the confinement scale using a point-like description for the B-meson. I will show that depending on the cut on final state radiation and on the lepton flavor the contribution from excited states of the B meson can become important.

Speaker: Max Ferre (JGU (Mainz))

FERRE_DESY_2024.pdf

46 Searching for LNV in rare meson decays

We investigate the possibility of disentangling different new physics contributions to the rare meson decays $K\rightarrow\pi+$invisible and $B\rightarrow K(K^*)+$invisible through kinematic distributions in the missing invariant mass squared. We employ dimension-$6$ operators within the Low-Energy Effective Field Theory (LEFT), identifying the invisible part of the final state as either active or sterile neutrinos. Special emphasis is given to lepton-number violating (LNV) operators. We show analytically that contributions from vector, scalar, and tensor quark currents can be uniquely determined from experimental data of kinematic distributions. As there could \textit{a priori} also be new invisible particles in the final states, we include dark-sector operators giving rise to two dark scalars, fermions, or vectors in the final state. We show that careful measurements of kinematic distributions make it theoretically possible to disentangle the contribution from LEFT operators from most of the dark-sector operators, even when multiple operators are contributing. Finally, we point out that an excess in rare meson decays consistent with a LNV hypothesis would point towards highly flavor non-democratic physics in the UV, and could put high-scale leptogenesis under tension.

Speaker: Martin Mojahed (JGU/ TUM)

DESY24_Mojahed.pdf

47 Composite Higgs with Flavour Deconstruction

In this talk, we present a flavour non-universal UV completion of the Standard Model aimed at addressing the Higgs hierarchy problem and the flavour puzzle. In the UV, a flavour non-universal gauge sector is spontaneously broken down​ by non-perturbative dynamics. The Higgs emerges as a light pseudo-Nambu-Goldstone boson of the broken symmetry, and its potential is radiatively generated by explicit symmetry-breaking terms. We will provide a detailed description of the model and its appealing features in addressing the Higgs hierarchy problem and the flavour puzzle, in particular the positive impact of combining flavour non-universality with Higgs compositeness and a relatively close-by symmetry-breaking scale to the SM. We will also explore the model's rich phenomenology at the TeV scale and the related constraints from EWPOs, flavour observables and Higgs couplings modifications. We stress that our model is compatible with current experimental bounds and can provide TeV scale New Physics that simultaneously stabilizes the Higgs mass and addresses the flavour puzzle while evading the stringent flavour and Electroweak constraints.

Speaker: Marko Pesut (University of Zürich)

Marko_Pesut_DESY_Talk.pdf

16:00 Coffee break

48 When to interfere with dark matter? The impact of wave dynamics on statistics

Ultralight candidates for dark matter can present wavelike features on astrophysical scales. Full wave based simulations of such candidates are currently limited to box sizes of 1-10 Mpc/$h$ on a side, limiting our understanding of the impact of wave dynamics on the scale of the cosmic web. We present a statistical analysis of density fields produced by perturbative forward models in boxes of 128 Mpc/$h$ side length. Our wave-based perturbation theory maintains interference on all scales, and is compared to fluid dynamics of Lagrangian perturbation theory. The impact of suppressed power in the initial conditions and interference effects caused by wave dynamics can then be disentangled. We find that changing the initial conditions captures most of the change in one-point statistics such as the skewness of the density field. However, different environments of the cosmic web, quantified by critical points of the smoothed density, appear to be more sensitive to interference effects sourced by the quantum potential. This suggests that certain large-scale summary statistics may need additional care when studying cosmologies with wavelike dark matter.

Speaker: Prof. Cora Uhlemann (Bielefeld University)

Talk_WhenToInterfereDarkMatter_DESY.pdf

49 Bounds on ultralight dark matter from NANOGrav

The compelling evidence for the detection of the stochastic gravitational wave background by NANOGrav imposes constraints on the mass of compact cores of ultra-light dark matter, also known as “solitons”, surrounding supermassive black holes found at the centers of large galaxies. The strong dynamical friction between the rotating black holes and the solitons competes with gravitational emission, resulting in a suppression of the characteristic strain in the nHz frequency range. Our findings robustly rule out ultralight dark matter particles with masses ranging from 1e-21 to 1e-20 eV condensing into solitons around supermassive black holes.

Speaker: Mohammad Aghaie (University of Pisa and INFN Pisa)

ULDM_Mohammad_Aghaie.pdf

50 Fuzzy dark matter meets galaxy formation with IllustrisTNG

Ultra-light dark matter models, which feature particles whose masses are so light that their behavior can be treated as a collective wave rather than individual particles, are an intriguing alternative to “standard” cold dark matter. They feature a rich and unique phenomenology on astrophysical scales, with implications for small-scale tensions. The most well-studied member of this family is commonly called fuzzy dark matter, where dark matter is composed of scalar particles with a mass of $\sim 10^{-22}\,\mathrm{eV}$. Although strong constraints have been placed on this particular model, it remains an important benchmark to understand structure formation in more general wave dark matter scenarios, and because of computational limitations encountered in numerical simulations of wave dark matter.

While simulation efforts for fuzzy dark matter have thus far mainly focused on understanding its properties in a dark matter-only context, i. e. without including baryonic matter, the coupling of both matter components has hardly been studied and remains poorly-understood. In particular, it is unclear to what extent the presence and gravitational influence of baryonic matter modifies the conclusions obtained in this manner, and in turn, how strongly the unique behavior of fuzzy dark matter affects important baryonic processes and astronomical observables, such as star and galaxy formation.

In this talk, I will present numerical simulations of cosmic structure formation with fuzzy dark matter, and highlight the unique signatures of fuzzy and other ultra-light dark matter models. In particular, I will focus on new cosmological fuzzy dark matter simulations including baryons, using the IllustrisTNG galaxy formation model, which provide invaluable data in a more realistic scenario.

Speaker: Simon May (Perimeter Institute)

Simon_May_2024-09-25.pdf

51 Searching for Ultralight ALPs using JVLA and VLBA Observations

Axionlike particles (ALPs) are promising candidates for dark matter. A tiny interaction between photons and ALPs gives rise to achromatic birefringence. The birefringence angle oscillates with a time period determined by ALP mass. We exploit this property of ALPs to find stringent constraints on its coupling constant as well as mass by means of radio polarimetric observations of strong gravitationally lensed quasars.

The differential polarization angle measured between the images of strong gravitationally lensed quasars is expected to exhibit a clean ALP-induced birefringence signal which is free of observational and astrophysical systematics. This allows us to probe ALPs at sensitivity comparable to, or better than, lab experiments. We demonstrate this new technique with the help of existing observations. We also report about the ongoing analysis of ∼100 hours of dedicated multi-epoch spectropolarimetric observations of 5 gravitational lens systems using the JVLA and the VLBA.

Speaker: Shivani Deshmukh (Bielefeld University)

Deshmukh_DESY24.pdf

52 Multiple Soft Scatterings in Freeze-In Dark Matter Production

In this talk, we address the impact of the hot plasma during dark matter production via freeze-in. In particular, we study a model that features a feebly-interacting real scalar and a vector-like mediator. Recent work has shown that, in contrast to freeze-out production in the context of WIMPs, freeze-in production is sensitive to thermal corrections. While previous calculations had not included multiple soft scatterings with the plasma, an effect known as the so-called Landau-Pomeranchuk-Migdal (LPM) effect, we include the LPM effect for the first time in this model and discuss the impact on the prediction of the dark matter relic density.

Speaker: María José Fernández Lozano (JGU Mainz)

Multiple Soft Scatterings.pdf

53 Riding the dark matter wave: Novel limits on general dark photons from LISA Pathfinder

I demonstrate the possibility to perform a parametrically improved search for gauged baryon ($B$) and baryon minus lepton ($B-L$) Dark Photon Dark Matter (DPDM) using auxiliary channel data from LISA Pathfinder. In particular I point out the use of the measurement of the differential movement between the test masses (TMs) and the space craft (SC) which is nearly as sensitive as the tracking between the two TMs. TMs and SC are made from different materials and therefore have different charge-to-mass ratios for both $B-L$ and $B$. Thus, the surrounding DPDM field induces a relative acceleration of nearly constant frequency. For the case of $B-L$, I show that LISA Pathfinder can constrain previously unexplored parameter space, providing the world leading limits in the mass range $4\cdot 10^{-19}\,\text{eV}

Speaker: Jonas Frerick (T (Theorie))

dpdm_lpf_jf.pdf

Parallel Wednesday Pheno 2

54 Ruling out g-2 in $L_\mu-L_\tau$ with White Dwarf Cooling

In this talk, I will present the first ab initio computation of white dwarf (WD) cooling due to plasmon decay in a model of gauged $U(1)_{L_\mu-L_\tau}$. In particular, I will present the full result taking into account resonance effects of the $A'$ mass with the WD plasma frequencies.

I will show how current observations of the neutrino luminosity function of early-stage WDs exclude previously allowed regions of the parameter space favoured by a simultaneous explanation of the $(g-2)_\mu$ and $H_0$ anomalies.

Speaker: Patrick Foldenauer (IFT UAM-CSIC Madrid)

foldenauer_desy24.pdf

55 QCD axion couplings in dense matter and astrophysical bounds

As an elegant solution to the strong CP problem and promising dark matter candidate, the QCD axion is one of the best motivated particles beyond the SM. The hunt for the QCD axion, both with terrestrial experiments as well as astrophysical observables, has exploded in the last years. As of today, astrophysical observations, such as neutron star cooling and energy loss from supernovae, place the strongest bounds.
In this talk, I will show that astrophysical bounds depend on a non-trivial momentum dependence of the axion-nucleon coupling in zero- as well as in finite density environments. This dependence is induced by one-loop corrections to the coupling that can be systematically calculated within the framework of chiral perturbation theory, both at zero density and in thermal field theory. As a consequence, the supernova bound is strengthened and the momentum dependence further allows us to constrain large parts of parameter space of the axion neutron coupling.
Additionally, I will talk about the model independent axion production mechanism in supernova, leading to a orders of magnitude stricter bound than in current literature, where the operator responsible for the dominant model independent contribution has been neglected so far.

Speaker: Michael Stadlbauer (MPP/TUM)

Presentation_Axion_DESY.pdf

56 White Dwarfs as Laboratories for New Scalar Fields

New light scalar fields with a negative quadratic coupling to Standard Model fermions can be sourced in large, dense objects. Finite density contributions to the potential result in the displacement of the field from its vacuum value. This situation arises, for example, for a lighter-than-usual QCD axion. The sourcing of the scalar field leads to a reduction of the fermion masses, which, depending on the scalar field's coupling and mass, can result in a first-order phase transition or a new ground state of matter.

White dwarfs are well understood and therefore provide ideal laboratories to observe these effects. The presence of a new ground state predicts a gap in the possible radii of white dwarfs, which is inconsistent with observational data. Including finite temperature effects gives access to further observables, which allows us to also constrain first-order phase transitions arising from new scalar fields. This excludes large regions of parameter space without the necessity for the new scalar field to be dark matter.

Speaker: Kai Bartnick (TU Munich)

KB_WD_LaboratoriesForNP_DESY_24.pdf

57 Constraining light QCD axions with NS cooling

Lighter than expected QCD axions can get sourced in neutron stars, which can lead to a new ground state of nuclear matter, reminiscent of strange quark matter. The presence of such a new ground state drastically changes the stellar composition of neutron stars; in particular, in the limit where axion gradient effects can be neglected, the star ends with an extremely large energy density. This prevents the existence of heat-blanketing envelopes; a low-density phase in which the isothermal core temperature drops towards the surface by several orders of magnitude and dictates the cooling behavior. In the absence of such envelopes, the surface temperature would hence be orders of magnitude larger, resulting in the same increase in the cooling rate. Confrontation with data allows to probe large regions of previously unexplored axion parameter space.

Speaker: Konstantin Springmann (Weizmann Institute)

KS_DESY.pdf

58 Naturally small neutrino mass with asymptotic safety and gravitational-wave signatures

We revisit the dynamical generation of an arbitrarily small neutrino Yukawa coupling in the Standard Model with trans-Planckian asymptotic safety and apply the same mechanism to the gauged B − L model. We show that thanks to the presence of additional irrelevant couplings, the described neutrino-mass generation in the B − L model is potentially more in line with existing theoretical calculations in quantum gravity. Interestingly, the model can accommodate, in full naturalness and without extensions, the possibility of purely Dirac, pseudo-Dirac, and Majorana neutrinos with any see-saw scale. We investigate eventual distinctive signatures of these cases in the detection of gravitational waves from first-order phase transitions. We find that, while it is easy to produce a signal observable in new-generation interferometers, its discriminating features are washed out by the strong dependence of the gravitational-wave spectrum on the relevant parameters of the scalar potential

Speaker: Mr Abhishek Chikkaballi Ramalingegowda (National Centre for Nuclear Research, Warsaw)

Abhishek_Final.pdf

59 A Coordinate-Independent Formalism for Detecting High-Frequency Gravitational Waves

In an external electric or magnetic field, a gravitational wave (GW) may be converted into electromagnetic radiation. We present a coordinate-invariant framework to describe the GW signal in a detector that is based on this effect, such as cavities for axion searches. In this framework, we pay special attention to the definition of manifestly coordinate-independent expressions for the electromagnetic fields that an external observer would detect. A careful assessment of the detector's perceived motion allows us to treat both its mechanical and its electromagnetic response to the GW consistently. We illustrate our findings in two examples, an infinitesimally thin rod and a spherical electromagnetic cavity.

Speaker: Sebastian Schenk (JGU Mainz)

desy2024_hfgw.pdf

60 Effective Field Theory Approach to Binary Systems in Scalar-Tensor Theories

Theories beyond General Relativity typically contain at least one additional scalar degree of freedom, effectively mediating an additional force. While this force must be highly suppressed in low-density environments--to pass current constraints--it generically leads to deviations from General Relativity in high-density / high-curvature environments, such as neutron stars and black holes, and thus impacts their observables. I will discuss how binary systems in scalar-tensor theories can be treated using an effective field theory approach and present results regarding observables such as the energy loss and the gravitational wave spectrum.

Speaker: Robin Fynn Diedrichs (Goethe University Frankfurt)

desy_talk_split.pdf

61 Impact of non-standard interactions on low-scale leptogenesis and neutrinoless double beta decay

In this talk, we investigate the interplay between the observation of lepton number violating processes and the generation of the baryon asymmetry of the Universe via low-scale leptogenesis. We focus on the impact of non-standard interactions, beyond the usual Majorana mass term, on the observation of neutrinoless double beta decay and the resulting parameter space for successful leptogenesis. Parameterizing these effects in a model independent way, we showcase how additional operators can influence the final baryon asymmetry.

Speaker: Sascha Weber (JGU Mainz)

DESY2024_Sascha_Weber.pdf

16:00 Coffee break

62 BBN photodisintegration limits from neutrino injections

Constraints on dark sector particles decaying into neutrinos typically focus on their impact on the effective number of relativistic species, $N_{eff}$, in the early Universe. However, for heavy relics with longer lifetimes, constraints mainly arise from the photo-disintegration of primordial abundances. The high-energy neutrinos injected by the decay can interact with both the thermal neutrinos and other high-energy neutrinos. Among these interactions, annihilations into electromagnetic particles will induce an electromagnetic cascade that affects the abundances of the already formed light elements via photo-disintegration. In this work, we present constraints on these dark sector particles. Specifically, we implement a code to simulate the electromagnetic cascade, instead of solving the full set of Boltzmann equations. We find improved bounds on the particle's lifetime, abundance, and mass.

Speaker: Sara Bianco (T (Phenomenology))

BBN_SB_DESYTheoryWorkshop2024.pdf

63 Kinetic Theory in space-time dependent background and a simple recipe for calculating CP-Violating Sources for Electroweak Baryogenesis

A persistent issue in electroweak baryogenesis calculations is the significant disparity in predictions yielded by different approaches, with variations spanning several orders of magnitude. In this study, we examine a system comprising two fermion flavours, proposing the existence of two sources of CP-violating. The semi-classical force and a new resonantly enhanced mixing source can be derived from the collisionless Kadanoff-Baym equation. The two sources are derived using the semiclassical approximation and the VEV insertion approximation. A Higgsino-Bino toy model shows that the new resonantly enhanced mixing source generates orders of magnitude higher asymmetry yield than the flavour diagonal semiclassical force.

Speaker: Bahaa Ilyas (Technical University of Munich)

Bahaa Ilyas Reciepe for EWBG - DESY 2024.pdf

Bahaa Ilyas Reciepe for EWBG - DESY 2024.ppsx

64 Functional Renormalization Approach to Baryogenesis.

Analysing Baryogenesis and employing techniques from Non-Equilibrium QFT and integrating them with Functional Renormalization, we demonstrate and calculate key quantities such as the Matter-Antimatter asymmetry and thermal masses and widths. This combination also allows us to re-examine the Sakharov conditions. Moreover, we elucidate the interconnections between various common methodologies.

Speaker: Apostolos Tsabodimos (Leibniz University of Hannover)

Hamburg_Presentation (5).pdf

65 Shaping Dark Photon Spectral Distortions

The cosmic microwave background (CMB) spectrum is an extraordinary tool to explore physics beyond the standard model. Due to the exquisite precision of its measurements, it constitutes a natural place to look for small effects due to the hidden universe. In particular, CMB spectral distortions can unveil the existence of dark photons which are kinetically coupled to the standard photon. In this work, we use the COBE-FIRAS dataset to derive self-consistent and robust limits on photon-to-dark-photon oscillations for a large range of dark photon masses, from $10^{-10}$ to $10^{-3}$ eV. We consider in detail the redshift dependence of the bounds, computing CMB distortions due to photon injection/removal using photon linearized Boltzmann equations. Our treatment supersedes previous works, which had set limits studying energy injection/removal rather than photon injection/removal or ignored the redshift dependence of the distortions. The difference between our treatment and previous ones is particularly noticeable in the spectral shape of the distortions, a smoking gun signature for photon-to-dark-photon oscillations. The spectral shape characterisation is crucial for future CMB missions -- a pillar of the ESA Voyage 2050 Program -- which could improve the present sensitivity by orders of magnitude, exploring regions of the dark photon parameter space that are otherwise extremely difficult to access.

Speaker: Xucheng Gan (DESY)

DESY_Th_2024.pdf

66 Electroweak Baryogenesis via Domain Walls in the N2HDM

Domain walls are a type of topological defects that can arise in the early universe after the spontaneous breaking of a discrete symmetry. This occurs in several beyond Standard Model theories with an extended Higgs sector such as the Next-to-Two-Higgs-Doublet model (N2HDM).

In this talk I will discuss the ingredients needed for the successful generation of a matter-antimatter asymmetry in the early universe using domain walls related to the singlet scalar of the N2HDM. I will first demonstrate the possibility of restoring the electroweak symmetry in the vicinity of the domain wall leading to an unsuppressed sphaleron rate inside the wall. I also discuss how domain walls in this model can generate CP-violating electroweak vacua localized on the vicinity of the wall which can provide the CP-violation condition for baryogenesis while naturally evading EDM constraints.

This mechanism has the advantage of being independent on the order of the electroweak phase transition as well as evade any EDM constraints on CP-violation.

Speaker: Mohamed Younes Sassi (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

DESY theory workshop final.pdf

67 Searches for BSM physics at a gamma-gamma collider with Energy < 12 GeV based on European XFEL

The possibility of a Gamma-Gamma collider extension to the Beam dump of the $17.5$ GeV European XFEL has been discussed before as a first high energy collider of its sort. It would not just be to study the concept of a gamma-gamma collider but this collider would also be without competition in the region of $5-12$ GeV for gamma-gamma physics. In this range $b\bar{b}$ and $c\bar{c}$ resonances, tetraquarks as well as mesonic molecules can be observed. Furthermore some BSM processes can also be reached in this range. In this talk we want to discuss the possibility of observing ALPs at this collider as well as an extension to a mixed model of ALPs and dark photon (dark axion portal), that introduces the new couplings not as a product of the individual couplings and therefore offers a rich phenomenology.

Speaker: Marten Berger (FLC (Forschung an Lepton Collidern))

GammaGammaCollider.pdf

Parallel Wednesday Strings & Mathematical Physics

68 Lagrangians insertions: cusp anomalous dimension and large spin

In the context of planar conformal gauge theory, we study five-point correlation functions between the interaction Lagrangian and four of the lightest single-trace, gauge-invariant scalar primaries. After performing two light-cone OPEs, we express this correlator in terms of the three-point functions between two leading-twist spinning operators and the Lagrangian. For finite values of spin, we compute these structure constants in perturbation theory up to two loops in N = 4 Super Yang–Mills theory. Large values of spin are captured by null polygon kinematics, where we use dualities with null polygon Wilson loops as well as factorization properties to bootstrap the universal behavior
of the structure constants at all loops. We find explicit maps that relate the Lagrangian structure constants with the leading-twist anomalous dimension. From the large-spin map, we recover the cusp anomalous dimension at strong and weak coupling, including genus-one terms.

Speaker: Carlos Bercini Vargas (T (Stringtheory))

LagrangianTalk-1.pdf

69 Radial canonical AdS3 gravity and TTbar

We discuss the radial canonical formalism for asymptotically AdS$_3$ gravity. We employ an ADM deparametrization procedure that allows the identification of a preferred 'time' before quantization, the volume time, which is canonically conjugate to York time. This leads to the identification of the (radial) Wheeler-DeWitt (WdW) equation with the Schr\"odinger equation in volume time. In the context of holography, the WdW equation is interpreted as the flow generated by the $T\bar{T}$ deformation of a 2-dimensional CFT living on the conformal boundary of AdS$_3$. Unlike previous works, we discuss this duality using the natural language provided by the volume time identification.
Later we make this duality explicit by applying the radial canonical formalism to a concrete example: the BTZ black hole, where we find the correspondence between the conserved charges and the $T\bar{T}$ spectrum.

This talk will be based on 2406.02508, with M. Blacker., N. Callebaut and S. Ning.

Speaker: Blanca Hergueta Aragon (Universität zu Köln)

DESY_BlancaHergueta.pdf

70 Ensemble averages of Z2 orbifold classes of Narain CFTs

In this work we study families of Z2 orbifolds of toroidal conformal field theories based on both factorizable and non-factorizable target space tori. For these classes of theories, we analyze their moduli spaces, and compute their partition functions. Building on previous work, we express the calculated partition functions in terms of suitable Siegel-Narain theta functions that allow us to determine their ensemble averages. We express the derived averaged partition functions of the studied families of conformal field theories in a manifest modular invariant finite sum of products of real analytic Eisenstein series. We speculate on a tentative holographic three-dimensional dual bulk interpretations for the considered Z2 orbifold classes of ensembles of conformal field theories.

Based on arXiv:2403.02976 with Stefan Forste, Hans Jockers, Joshua Kames-King and Ida G. Zadeh.

Speaker: Alexandros Kanargias (University of Mainz (JGU))

Kanargias.pdf

71 Is M-theory emergent?

In this talk, I will present recent progress in the Swampland Program, which I will briefly introduce, focusing primarily on one of its less established conjectures, usually referred to as the Emergence Proposal. This postulates that the low energy effective action of a quantum gravity theory may be obtained by integrating out light towers of states appearing in various asymptotic regions of the moduli space. I will motivate why the Emergence Proposal seems to be naturally realized in the (not yet completely understood) decompactification limit to M-theory by reviewing recent calculations of higher derivative couplings and independent arguments.

Speaker: Antonia Paraskevopoulou (MPI)

Desy_Parallel_Paraskevopoulou.pdf

72 Arithmetic aspects of Gepner Models

There is growing evidence that the geometries associated to rational conformal field theories (RCFTs) which have a target space interpretation are distinguished by the fact that they admit complex multiplication (CM). I will show where this intuition naturally originates from in the context of toroidal CFTs (Work by Gukov, Vafa and Moore) and generalize the idea to higher dimensions. In particular I will show how the quantum symmetries present in all Gepner models equip the associated geometries with an enlarged Hodge endomorphism algebra that fulfills the CM criteria. I will comment on relations to attractor points and motives. This is based on work in progress with Hans Jockers and Pyry Kuusela.

Speaker: Maik Sarve

talk.pdf

73 Coordinate Bethe Ansatz for N=2 SCFTs

Abstract: The study of the spectral problem of planar $\mathcal{N}=2$ SCFTs and their corresponding spin chains have been an inauspicious problem. In this talk I want to present a novel approach to the coordinate Bethe Ansatz which allowed the computation of the three-magnon wave function (paper to appear) for the spin chains that capture the spectral problem of the marginally deformed $\mathbb Z_2$ orbifold of $\mathcal{N}=4$ SYM in planar limit. The novel idea is the introduction of contact terms which incorporate the dynamical structure of the spin chains and it can be generalized to n-body problem and also to more general orbifolds.

Speaker: Deniz Bozkurt (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

desy_theory_workshop2_deniz_bozkurt.pdf

74 Local-in-time conservative binary dynamics at fourth Post-Minkowskian Order

The Post-Minkowskian expansion can efficiently describe the scattering of two massive compact objects emitting gravitational waves. In particular, the results at fourth order in Newton's constant already show remarkable agreement with numerical simulations. However, although the boundary-to-bound dictionary allows analytic continuation of local-in-time results to the case of two coalescing objects, the nonlocal-in-time contributions need to be computed and removed for this to be possible. In this talk, I will describe these computations and how they will enhance our ability to make accurate predictions for gravitational waveforms.

Speaker: Christoph Dlapa (Z_THAT (Theoretische Gravitationswellenastrophys))

DESY_THW_2024_vector_singleslide.pdf

16:00 Coffee Break

75 False vacuum decay of excited states from finite-time instantons

We adapt the well-known functional instanton method to allow for the computation of excited state decay widths, efficiently bypassing the traditionally enforced infinite-time limit. With conventional instanton calculations relying on the behavior of the Euclidean propagator at late times, such investigations are, per construction, constrained to solely studying the ground state energy. By suitably projecting out the desired resonant energies using appropriate eigenfunctions, we demonstrate that the common path integral formalism can be generalized to accommodate excited state decay. We explicitly determine the sought-after decay widths, including leading quantum corrections, for arbitrary potentials, demonstrating accordance with traditional WKB results.

Speaker: Nils Wagner

Talk_DESY_Wagner.pdf

76 Modular invariant Inflation

We propose new classes of inflation models based on the modular symmetry, where the modulus field $\tau$ serves as the inflaton. We establish a connection between modular inflation and modular stabilization, wherein the modulus field rolls towards a fixed point along the boundary of the fundamental domain. We find the modular symmetry strongly constrain the possible shape of the potential and identify some parameter space where the inflation predictions agree with cosmic microwave background observations. The tensor-to-scalar ratio is predicted to be smaller than $10^{-6}$ in our models, while the running of spectral index is of the the order of $10^{-4}$.

Speaker: Wenbin Zhao (BCTP, Uni.Bonn)

DESY24_WenbinZhao.pdf

77 Preheating the String Axiverse: non-perturbative production of stringy axions

The standard reheating process after inflation can be preceded by preheating, a phase where the oscillations of the inflaton field at the bottom of its potential lead to explosive production of particles via parametric resonance, potentially altering the history of the universe.
I will discuss an inflating modulus, coupled to an axion via a typical potential coupling coming from type iib string theory on Calabi-Yau orientifolds and explore the consequences of parametric resonance in the string axiverse.

Speaker: Margherita Putti (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

2024.DesyTheoryWorkshop_Margherita_Putti.pdf

78 Recent progress on inflation and dark energy from string theory

I will discuss recent progress in constructing models of inflation and dark energy from string theory which are theoretically robust, can fit current data and can lead to observable predictions. In particular, I will focus on inflation driven by a Kaehler modulus and I will argue that axions are the best candidates to drive dark energy.

Speaker: Michele Cicoli (Bologna University)

DESY_Cicoli.pdf

79 A quantum improved description of false vacuum decay via the 2PI effective action formalism

False vacuum decay is believed to have played an important role in the history of the universe, in particular in the context of phase transitions in the very early universe. As such, a microscopic understanding of the process is crucial to our ability to make predictions. In this talk, we review the traditional instanton method for the computation of the false vacuum decay rate, and we improve it by embedding it in the 2PI effective action formalism. In particular, we show how the formalism is capable of correctly capturing the quantum corrected spectrum of fluctuations, and is therefore a powerful tool to deal with softly broken symmetries and quasi-zero modes.

Speaker: Matthias Carosi (TUM)

DESY_2024-1.pdf

Thursday 26 September

Plenary Sessions Thursday I

Convener: Bruce Allen

80 LISA: the challenges and the high gain science return

Speaker: E. M. Rossi

DESY_theory_symposium_ROSSI.pdf

81 Stochastic GW Background Searches at LISA

Speaker: Valerie Domcke (CERN)

DESY_theory_workshop_2024(1).pdf

82 EFT for GW

Speaker: R. Porto

desy24.pdf

11:00 Coffee break

Plenary Sessions Thursday II

Convener: Laura Sagunski (Goethe University Frankfurt)

83 Continuous Gravitational Waves from Neutron Stars

Speaker: M.A. Papa

PapaDesyTheoryWorkshopShared.pdf

84 Line Intensity Mapping

Speaker: M. Kamionkowski

mk_desy2024.pdf

12:50 Lunch

Parallel Thursday Cosmo 1

85 From vacuum decay to gravitational waves

Cosmological phase transitions are events during which the universe evolves from a metastable state to a stable state, through a process of bubble nucleation. The bubbles of the stable phase expand, collide, and interact with the cosmic fluid, leading to the production of gravitational waves. Such signals could be detectable by current and upcoming interferometer experiments.
This presentation focuses on recently developed numerical tools and analytical techniques for the calculation of phase transition parameters and gravitational waves spectra.

Speaker: Marco Matteini (Jozef Stefan Institute, University of Ljubljana)

Matteini_DESY.pdf

86 Gravitational waves from confinement in improved holographic QCD

I will discuss gravitational waves produced during the confinement phase transition in SU(N) Yang-Mills, using a holographic description. I will highlight the role of the kinetic term of the effective action.

Speaker: Enrico Morgante (U. Trieste & INFN)

Morgante_DESY_2024.pdf

87 The Baryon Asymmetry from Supercooled Confinement

I will present a new framework for baryogenesis and leptogenesis based on a supercooled confining first order phase transition (PT).
With respect to the case of weakly coupled PTs, the rate asymmetry is enhanced by the decays of hadrons of the strong dynamics after the PT and washout effects from inverse decays are suppressed.
Therefore, our setup extends the parameter space of successful generation of the baryon asymmetry down to TeV scale PTs, making it testable with gravity waves at LISA and the Einstein Telescope.
I will discuss two specific realizations of our framework, one of baryogenesis and one of leptogenesis and show how our setup can make their phenomenology partially testable. I will finally comment about the connection between our framework with open SM problems in addition to the generation of the baryon asymmetry.

Speaker: Jacopo Nava (University of Bologna)

DESY_Nava.pdf

88 Leptogenesis via Bubble Collisions

We present a novel realization of leptogenesis from the decays of sterile (right-handed) neutrinos (RHNs) produced from runaway bubble collisions at a first order phase transition. Such configurations can produce heavy RHNs with mass many orders of magnitude above the scale of symmetry breaking, thereby enabling (non-resonant) leptogenesis without the need for high reheat temperatures while also naturally suppressing washout effects. This mechanism also extends the window of viability to RHN masses $\gtrsim 10^{14}$ GeV, the natural scale for type-I seesaw with $\mathcal{O}(1)$ couplings, where standard thermal leptogenesis cannot produce the observed baryon asymmetry. The corresponding phase transitions are at scales $\gtrsim\!10^8$ GeV and can produce gravitational wave signals within reach of future experiments.

Speaker: Martina Cataldi (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

Cataldi_BubbleLepto1.pdf

89 Supercooled phase transition reconciles (stepped) dark radiation solutions to the Hubble tension with BBN

We propose a simple model that can alleviate the $H_0$ tension while remaining consistent with big bang nucleosynthesis (BBN). It is based on a dark sector described by a standard Lagrangian featuring a $SU(N)$ gauge symmetry with $N\geq3$ and a massive scalar field with a quartic coupling. The scalar acts as a dark Higgs leading to spontaneous symmetry breaking $SU(N)\to SU(N\!-\!1)$ via a first-order phase transition `a la Coleman-Weinberg. This set-up naturally realizes previously proposed scenarios featuring strongly interacting dark radiation (SIDR) with a mass threshold within hot new early dark energy (NEDE). For a wide range of reasonable model parameters, the phase transition occurs between the BBN and recombination epochs and releases a sufficient amount of latent heat such that the model easily respects bounds on extra radiation during BBN while featuring a sufficient SIDR density around recombination for increasing the value of $H_0$ inferred from the cosmic microwave background. Our model can be summarized as a natural mechanism providing two successive increases in the effective number of relativistic degrees of freedom after BBN but before recombination $\Delta N_\mathrm{BBN} \to \Delta N_\mathrm{NEDE} \to \Delta N_\mathrm{IR}$ alleviating the Hubble tension. The first step is related to the phase transition and the second to the dark Higgs becoming non-relativistic. This set-up predicts further signatures, including a stochastic gravitational wave background and features in the matter power spectrum that can be searched for with future pulsar timing and Lyman-$\alpha$ forest measurements.

Speaker: Henrique Rubira (TUM)

DESY_HNEDE_24_09_26.pdf

90 EFT for supercooled phase transitions

"We analyze the role of higher-order thermal corrections for supercooled phase transition, and to what extent they can be computed using dimensionally reduced effective field theory (3D EFT). This framework requires high-temperature (HT) expansion to be valid, which seems challenging due to the presence of supercooling. We show how to reliably use the HT expansion in dimensionally reduced theory for the calculation of bubble nucleation rate, and apply it to a classically scale-invariant model
These corrections affect the predictions significantly e.g. transition temperature and scale. We compare new results to the ones obtained using the most common scheme based on the so-called daisy resummation. "

Speaker: Maciej Kierkla (University of Warsaw)

desy24_mkierkla.pdf

91 Bubble misalignment mechanism

We study the dynamics of axions at first-order phase transitions in non-Abelian gauge theories. When the duration of the phase transition is short compared to the timescale of the axion oscillations, the axion dynamics is similar to the trapped misalignment mechanism. On the other hand, if this is not the case, the axions are initially expelled from the inside of the bubbles, generating axion waves on the outside. Analogous to the Fermi acceleration, these axions gain energy by repeatedly scattering off the bubble walls. Once they acquire enough energy, they can enter the bubbles. The novel ``bubble misalignment mechanism'' can significantly enhance the axion abundance, compared to models where the axion mass is either constant or varies continuously as a function of temperature. The increase in axion abundance depends on the axion mass, the duration of the phase transition, and the bubble wall velocity. This mechanism results in a spatially inhomogeneous distribution of axions, which could lead to the formation of axion miniclusters. It has potential implications for the formation of oscillons/I-balls, axion warm dark matter, cosmic birefringence, and the production of dark photons.

Speaker: Fuminobu Takahashi (Tohoku University)

Takahashi0926.pdf

92 Gravitational waves and baby black holes from super-slow first-order phase transition

Recently, cosmological first-order phase transition (FOPT) that slowly takes place has attracted much attention. On one hand, it predicts larger amplitude of stochastic gravitational wave background (SGWB), which is actually in a nice agreement with the recent PTAs result. On the other hand, inhomogeneity during FOPT may lead to the formation of primordial black holes (PBHs). In our study, we consider possibly the slowest realization of the cosmological FOPT, where the FOPT is catalyzed by the seed PBHs with sparse distribution. We found that this scenario predicts collision of large bubbles sourcing SGWB detectable with future observations. At the same time, rare patches inflate into causally disconnected baby universes causally disconnected. These are seen as black holes from the universe in the true vacuum and can reproduce the dark matter abundance. We also discuss the constraints and observational prospects of this scenario.

Speaker: Jun'ya Kume (UNIPD, INFN, RESCEU)

DESY_Theory_Workshop_JK.pdf

16:08 Coffee break

93 Nano-Hertz gravitational waves and sub-GeV dark matter form a nearly conformal phase transition

The 15 year data release of the pulsar timing array (PTA) observatory NANOGrav has given decisive evidence for a stochastic gravitational wave (GW) signal at nano-Hertz frequencies. The standard astrophysical explanation of the data -- merging black hole binaries -- can be improved by introducing an additional cosmological source of a stochastic GW signal. An intriguing possibility for this is a first order phase transition. In this talk, I will consider a scenario where the spontaneous symmetry breaking of a classical conformal model gives rise to first order phase transition and to a stochastic GW signal that can fit the PTA data. Additionally, the symmetry breaking sources the mass of a fermionic sub-GeV dark matter candidate that can reproduce the observed relic abundance via the freeze-out mechanism. Finally I will discuss collider and cosmological constraints for the model.

Speaker: Jonas Matuszak (Karlsruhe Institute of Technology (KIT))

JM_DESY24.pdf

94 Impact of theoretical uncertainties on model parameter reconstruction from gravitational wave signals sourced by cosmological phase transitions

Different thermal resummation techniques impact the gravitational wave (GW) spectra from cosmological first-order phase transitions predicted in a given particle physics model. To investigate this effect, we perform large-scale parameter scans of the electroweak phase transition (EWPT) in the dynamical real-singlet extension of the Standard Model (SM) using three different perturbative approximations of the effective potential. While predictions of the GW amplitudes from the common, four-dimensional (4D) Daisy-resummed potentials are unreliable compared to state-of-the-art dimensionally reduced (3D) potentials, I will demonstrate that the overall detectable parameter spaces are robust up to a few percent in uncertainty. Regarding the reconstruction of the model parameters given a GW signal, I will illustrate that theoretical uncertainties however remain dominant over the experimental ones when using 4D standard techniques. Three-dimensional thermal effective theory, on the other hand, is accurate already at one-loop order, therefore providing the most promising route towards robust predictions for upcoming GW observatories.

Speaker: Daniel Schmitt

Schmitt_DESY_final.pdf

95 The Equation of State of the Universe after a First Order Phase Transition

The dynamics of a cosmological first order phase transition are governed by the interactions of a scalar field, which tunnels to a new vacuum state and results in the nucleation of bubbles. If the interactions of the scalar field with the plasma are sufficiently weak, instant reheating can not be assumed and the energy density of the universe is dominated by the field oscillations after the phase transition. It is commonly assumed that such a scenario would lead to a phase of matter domination. In this talk, I will revisit this assumption using results from lattice simulations, in which we investigate the energy budget of the scalar field dynamics and determine the equation of state of the system after the phase transition. These findings have relevant implications for the subsequent reheating and dark matter production.

Speaker: Henda Mansour (Karlsruhe Institute of Technology (TTP))

HendaMansour-DESY-Th-Workshop2024.pdf

Parallel Thursday Cosmo 2

96 Investigating cosmic histories with a stiff era through Gravitational Waves

We investigate the potential of gravitational-wave background searches to constrain cosmic histories characterised by a stiff equation of state, preceded by a period of matter domination. Such a scenario leads to a characteristic peak in the primordial gravitational-wave spectrum originating from cosmological inflation. Assuming instant transitions between distinct epochs, which allows an analytical treatment of the gravitational-wave spectrum, we perform a Bayesian inference analysis to derive constraints from the first three observing runs of the LIGO-Virgo-KAGRA Collaboration. Additionally, we consider a smooth transition, employing an axion-like particle physics model, and highlight the difference with the instant transition approximation. We then forecast detection prospects for such a cosmic history through future gravitational-wave experiments.

Speaker: Hannah Duval (Vrije Universiteit Brussel)

Hannah_Duval_DESY.pdf

97 The (first) LISA miracle

The recent adoption of the LISA mission by the European Space Agency marks a significant milestone for gravitational wave cosmology, offering unprecedented sensitivity to gravitational wave backgrounds emitted at temperatures around a few hundred GeV. Intriguingly, this temperature range not only corresponds to the electroweak epoch but also coincides with the scale at which the freeze-out of WIMP dark matter is expected to happen. In this talk, I will present our recent work demonstrating how dark matter freeze-out triggered by a strong first-order phase transition in a dark sector can produce gravitational waves in the milli-Hertz range. Our findings suggest that a gravitational wave background detected by LISA could indicate such a phase transition, pointing to a specific dark matter candidate and opening new avenues for exploring the connection between dark matter and gravitational waves.

Speaker: Carlo Tasillo (T (Cosmology))

2024_09_26_DESY_theory_workshop_Carlo_Tasillo.pdf

98 A bound on the lighest right-handed neutrino from wash-in Leptogenesis

In recent years, wash-in leptogenesis has emerged as a new mechanism to explain the baryon asymmetry of the universe. In contrast to other leptogenesis scenarios it does not require CP-violation in the right handed neutrino sector (RHN). Instead it relies on primordial charge asymmetries generated at higher energies which are washed into a non vanishing B-L asymmetry via RHNs.
In this talk we consider a nonzero primordial charge asymmetry in the right handed electrons and demonstrate how efficiently RHNs convert it into a B-L asymmetry in different temperature and mass regimes. Our main result is a lower bound on the lightest RHN mass, in the standard type-I seesaw mechanism, of 7-8 TeV from the requirement of successful wash-in leptogenesis.

Speaker: Mr Dominik Wilken (Münster University)

Lower_Bounds_Wash_In_Leptogenesis.pdf

99 Upper bound on thermal gravitational waves from hidden sectors

Hot viscous plasmas unavoidably emit a stochastic gravitational wave background similar to electromagnetic black body radiation. Presenting work published in 2312.13855, we study the hidden particle contribution to the background emitted by the primordial plasma in the early universe. While this contribution can easily dominate over that from Standard Model particles, we find that both are capped by a generic upper bound that makes them difficult to detect with interferometers in the foreseeable future. We finally illustrate our results by considering axion-like particles and heavy neutral leptons.

Speaker: Philipp Klose (Nikhef)

klose_DESY.pdf

100 Phase transitions with symmetry restoration - When does the bubble stop running?

We consider phase transitions with symmetry restoration, where particles
become massless inside the bubbles, and the leading order friction is
negative, causing the expanding bubble walls to accelerate, contrary to
standard phase transitions. We study the next to leading order
corrections arising from transition radiation in this case, which are
known to prevent runaway behavior in standard phase transitions. We find
that the friction component changes from negative to positive friction
as the wall boost factor increases to moderate values, so that runaway
behavior occurs for longer compared to standard transitions but
terminates at intermediate regimes.

Speaker: Julia Ziegler (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

bubbles_talk_16_v_1.pdf

101 Cosmic Last Scattering as an Axion Dark Matter Detector

Isotropic Birefringence — all-sky rotation of linear polarization — of the cosmic microwave background (CMB) can be sourced by axion-like particle dark matter. We predict distinct signals from oscillating ultra-light axion dark matter present at recombination as well as locally. Using Planck CMB upper limits while incorporating allowed axion fractions of dark matter, we find strong constraints on the axion-photon coupling which can improve over CAST limits by up to 5 and 2 orders, respectively, for recombination and local dark matter axions. Forecast constraints (Simons Observatory, LiteBIRD, CMB-S4, & CMB-HD) tighten further by 1-2 orders, extending to higher axion mass.

Improving hints of a detection (currently at ~3σ) of isotropic CMB birefringence from a re-analysis of Planck and WMAP data are considered, in light of our new axion birefringence signals. Certain regions of coupling-mass parameter space for ultra-light axion dark matter could explain this detection, if confirmed. We also present constraints from searches in the Planck data for time-oscillation of the birefringence.

CMB birefringence constraints scale only weakly with ultra-light axion fraction of dark matter. They remain unaffected by uncertainties common in other astrophysical axion probes: strength and spectrum of magnetic fields, assumed over-density of ALPs in structures and the source’s intrinsic polarization orientation.

Speaker: Pranjal Trivedi (Uni Hamburg)

Pranjal_Trivedi__CMB_LastScattering_axionDM_Detector__DESYTheoryWkshp_26Sep24.pdf

102 New early dark energy and its equation of state

The Hubble Tension is the discrepancy between the measured value of the Hubble parameter $H_0$ and its $\Lambda$CDM model prediction using the Planck CMB data. New Early Dark Energy (NEDE) addresses this tension using a triggered phase transition in the dark sector. In this work we constrain the phenomenological fluid model properties of NEDE using recent datasets. We allow the equation of state parameter, characterizing the post-phase transition fluid, to evolve in time. Our results indicate that data is compatible with a simple time dependence that could arise from a mixture of radiation and a stiff fluid. The model shows a significant reduction of the tension down to approximately $3σ$.

Speaker: Aleksandr Chatrchyan (Nordita)

chatrchyan.pdf

103 Fitting the DESI BAO Data with Dark Energy Driven by the Cohen--Kaplan--Nelson Bound

Gravity constrains the range of validity of quantum field theory. As has been pointed out by Cohen, Kaplan, and Nelson (CKN), such effects lead to interdependent ultraviolet and infrared cutoffs that may stabilize the dark energy of the universe against quantum corrections, if the infrared cutoff is set by the Hubble horizon. As a consequence of the cosmic expansion, this argument implies a time-dependent dark energy density. We confront this idea with the latest data from DESI BAO, Hubble and supernova measurements. We find that the CKN model provides a better fit to the data than the $\Lambda$CDM model and can compete with other models of time-dependent dark energy that have been studied so far.

Speaker: Mustafa Tabet

talk.pdf

16:08 Coffee Break

104 Exorcising the ghost condensate dark energy with a sextic dispersion relation

The universe's current acceleration is a pretty recent phenomenon in cosmological time scales. This means that the modes that have left our horizon since the beginning of the contemporary acceleration phase, have not really reached the exact IR limit. Noting this observation, we reconsider the possibility of having a ghost condensate as dark energy with a sixth-order dispersion relation. Looking at the three-point function of such a theory, we obtain the constraints on the coefficient of the sixth-order dispersion relation to avoid strong coupling. Such a ghost condensate if coupled to the standard model fields, induces a constant Lorentz-violating spin-dependent force, which can gravitate or anti-gravitate.

Speaker: Dr Amjad Ashoorioon (School of Physics, Institute for Research in Fundamental Sciences (IPM))

Sextic Ghost.pdf

105 Relic Neutrino Background from Cosmic Ray Reservoirs

The existence of a relic neutrino backgorund (R$\nu$B) is a major prediction of the standard cosmological model, but its detection is one of the hardest tasks in neutrino physics. The main challenge arises because of its extremely low energy, as a consequence of its low temperature $T_\nu\simeq 1.67×10^{−4}$ eV. The most promising experimental technique to detect the R$\nu$B is that of neutrino capture in tritium, as proposed for PTOLEMY, althoug the actual sensitivity to RνB remains uncertain. An intriguing detection possibility is that a fraction of the R$\nu$B has larger kinetic energies compared to that of the diffuse background. For instance, upscatterings of ultra-high-energy (UHE) cosmic rays (CRs) off the RnuB can accelerate relic neutrinos to UHE. In the case of large neutrino overdensities in the regions of space where the UHECRs-R$\nu$B interactons take place, the flux of boosted R$\nu$B can be sizeable enough to imprint signals at terrestrial facilities that look for UHE neutrinos. We discuss such possibility concentrating on galaxy clusters that act as CR-reservoirs. The long trapping times of UHECRs make this flux larger than that of R$\nu$B up-scattered by UHECRs en route to Earth. We find that IceCube excludes R$\nu$B overdensities larger than $\sim 10^{10}$ in galaxy clusters, and that future PUEO, RNO-G, GRAND and IceCube-Gen2 will test values down to $\sim 10^8$. Moreover, the flux of R$\nu$B boosted in this way exhibits a peculiar flavour composition, thus being distinguishable from other astrophysical UHE neutrino fluxes.

Speaker: Alessandro Granelli (University of Bologna and INFN)

BRnuB_Presentation.pdf

106 Constraints on f(R) gravity using gravitational wave emissions in pulsars

Pulsar observations were the beginning of gravitational wave measurements. They recently came into the focus again with the publications from pulsar timing array organisations. But not only the transmission of gravitational waves, also their emission can be investigated using these systems. With the growing number of very precise observations of pulsars in binary systems it became possible to measure their masses as well as the change of their orbital periods to high accuracy. This makes them prefect astrophysical laboratories to test general relativity as well as modifications of it via the total radiated power.

For this using $f(R)$ gravity with a general shape is a practical way to look for a broad range of high curvature corrections to GR. Over the dynamical equivalence to a GR plus a massive scalar field it also enables the search for dark matter in form of a large family of models of light scalar particles. The observations determining the sum of tensor radiation also present in GR and scalar radiation introduced by these models enables constraining them on many orders of magnitude for their masses with competitive results especially at the lower end of feasible mass range.

Speaker: Yannik Schaper (Goethe University Frankfurt (Institute for Theoretical Physics))

PulsarConstraintsYannikSchaper.pdf

Parallel Thursday Cosmo 3

107 TBA

Speaker: Lorenz Zwick

108 Signatures of Axion Stars in the Milky Way

Axion stars are coherent clumps of wavelike dark matter which are expected to form abundantly in dense structures like axion miniclusters. Due to their large central densities of up to $\rho_\star \sim 10^{23}\,$GeV$\,$cm$^{-3}$ at a QCD axion mass of $m_a=50\,\mu$eV, it has been conjectured that they can give rise to a number of different observable signatures. Among these signatures are the resonant radio conversion of axion dark matter in the magnetic fields of neutron stars, parametric resonance in suitable soliton profiles and the generation of relativistic axions in collapsing axion stars, also called Bosenovae.
We calculate the galactic event rates for these signals and summarize the results of our recent paper on collision rates of axion stars in the Milky Way. Our analysis shows that the collision rates between miniclusters and neutron stars can become as large as $\sim 10^5\,$yr$^{-1}$ galaxy$^{-1}$, but that the fraction of encounters which can lead to resonance between axion mass and magnetosphere plasma frequency is generally well below $\sim 1\,$yr$^{-1}$ galaxy$^{-1}$. This suggests that Bosenovae and parametric resonance are much more likely to lead to observable signatures than neutron star encounters. We also discuss how axion star accretion can additionally enhance the expected event rates for both Bosenovae and radio bursts.

Speaker: Dennis Maseizik (None)

Maseizik_DTW.pdf

109 Radio Emissions from Accreting Axion Stars

Axion-like particles, which we call axions, are promising dark matter candidates and may form substructures such as miniclusters and axion stars. When axions couple to photons, this interaction sets a critical axion star mass, which we call decay mass, above which parametric resonance of photons occurs. We consider the accretion of axion stars at decay mass within our galaxy and estimate the resulting radio line signals from these axion stars. We put constraints on the axion-photon coupling by comparing with observed radio backgrounds.

Speaker: Hyeonseok Seong (DESY)

Radio Emissions from Accreting Axion Stars.pdf

110 ALP production at finite temperature:

In this talk, we discuss the unphysical behavior that arises when addressing infrared (IR) divergences in particle production rates in cosmology, particularly focusing on axion production coupled to photons. This unphysical behavior manifests as negative production rates for soft axion momentum.
To address this, we calculate the axion production rate at finite temperature. Initially, we use the hard thermal loop (HTL) resummation, which is appropriate for soft momenta. Here, we find that the decay rate remains positive when resumming contributions from both photons. Furthermore, we extend the calculation beyond the HTL approximation, demonstrating that the decay rate remains positive across all momentum scales. This allows us , as well, to identify the deviations between both methods and identify the main contributions to the axion production rate.

Speaker: Cristina Puchades Ibáñez (Institute of Theoretical High Energy Physics (THEP)-Johannes Gutenberg Universität (JGU), Mainz)

CPI_DESY_talk24.pdf

111 Effects of PQ symmetry breaking on the production of QCD axion dark mattter through trapped misalignment

Does a QCD axion have room for enough Peccei-Quinn symmetry violation to impact the misalignment mechanism? Constraints from the neutron electric dipole moment tell us that the QCD axion must very nearly conserve PQ symmetry, but we also know that the symmetry is not perfect. Even a small amount of PQ breaking can have interesting phenomenology. We show how temperature-dependent PQ breaking can boost axion dark matter production through trapped misalignment. I will show what it takes for this mechanism to motivate dark matter for QCD axion masses much larger than usually expected, all the way up to the astrophysical limits.

Speaker: Dr Philip Soerensen (University of Padua / INFN Padua)

Presentation.pdf

112 Kinetic Axion from non-minimally coupled PQ Field

Axion Kinetic Misalignment can be generated by higher-order operators that explicitly break the PQ symmetry at very high energies. This results in a kick in the angular direction of the PQ field, causing a delay in the onset of axion oscillations. For the higher-order operator to be relevant, the PQ radial mode must reach very high values. We explore the possibility that a non-minimally coupled PQ field, with a $\xi R|\Phi|^2$ term, combined with a stiff era, can generate the exact initial conditions for a Kinetic Misalignment Mechanism.

Speaker: Riccardo Natale (DESY)

Axion Kinetic Misalignment from non-minimally coupled PQ field.pdf

113 High-frequency gravitational waves shining in photons in Galactic magnetic fields

High-frequency gravitational waves ($f\gtrsim1\,$MHz) are a smoking gun for the existence of exotic physics. Indeed, GW backgrounds generated in the early Universe could be characterized by high-frequency signals, allowing one to probe inflation, first-order phase transitions, topological defects and primordial black holes. The lack of current and future gravitational waves experiments sensitive at those frequencies leads to the need of employing different indirect techniques. Notably, one of the most promising one is constituted by graviton-photon conversions in magnetic fields. In this talk, I will focus on conversions of a stochastic gravitational wave background into photons inside the Milky-Way B-fields. I will discuss how graviton-to-photon conversions may lead to unexpected imprints in the Cosmic Photon Background (CPB) spectrum in the range of frequencies $f\sim10^{9}-10^{26}\,$ Hz. Hence, the absence of any significant evidence for a diffuse photon flux induced by gravitational-wave conversions induce stringent constraints on the gravitational-wave strain $h_c$.

Speaker: Alessandro Lella (INFN-National Institute for Nuclear Physics)

2024_DESY_Theory_Workshop_Lella.pdf

114 First Pulsar Polarization Array Limits on Ultralight Axion-like Dark Matter

Ultralight Axion-Like Dark Matter (ALDM) is characterized by its wave-like nature on astronomical scales and has a potential to address small-scale structure problems in local galaxies. As linearly polarized pulsar light travels through the ALDM galactic halo, its position angle can oscillate due to cosmic birefringence induced by the ALDM Chern-Simons coupling to electromagnetic field. Pulsar Polarization Array (PPA) is a powerful tool for detecting such an effect by cross-correlating the polarization signals across pulsars, and hence the ultralight ALDM. In this paper, we develop a framework to analyze the time-series data of PPA. We then conduct the first PPA analysis on ultralight ALDM, using the polarization data from 22 pulsars in the third data release of Parkes Pulsar Timing Array. For the mass range of $10^{−23}$ − $10^{−21}$ eV, our results surpass existing ones, pushing the limits on the ALDM Chern-Simons coupling to approximately $10^{−14}$ − $10^{−12}$ GeV$^{-1}$. Furthermore, we demonstrate that the cross-correlation of PPA data is crucial for characterizing the nature of the derived limits.

Speaker: Xiao Xue (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

DESY.key

DESY.pdf

16:08 Coffee break

115 Detecting Gravitational Wave Anisotropies from Supermassive Black Hole Binaries

Anisotropies play a central role in distinguishing between cosmological and astrophysical sources of the GWB, as detectable anisotropies are expected for a GWB from a population of supermassive black hole binaries (SMBHBs) but not for cosmological sources. A search for anisotropies in the NANOGrav 15-year dataset resulted in a null detection. We show that this null detection is not yet in tension with an SMBHB-generated background by calculating the detection probabilities for anisotropies for present and future PTAs. We find that a PTA with the noise characteristics of the NANOGrav 15-year dataset had only a ~6.5% probability for detecting anisotropies, whereas this probability might increase to ~16% for the IPTA DR3. We also identify SMBHB populations that are more likely to produce detectable levels of anisotropies. This information could be used together with the spectral properties of the GWB to characterize the SMBHB population.

Speaker: Anna-Malin Lemke (UHH)

Lemke_DESY.pdf

116 The impact of cosmic variance on PTAs anisotropy searches

After the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) reported evidence of an isotropic background of gravitational waves (GWB) at nanohertz in its 15-year data set, the next important step is to understand where this signal might come from. One way to do this is to look for the presence of anisotropies in it: this would help to distinguish an astrophysical origin, e.g. from supermassive black hole binaries (SMBHB), from a cosmological one, e.g. from a cosmological phase transition. So far, no significant evidence of anisotropy has been found. In our work, we investigated the impact that the inclusion of some previously neglected contributions in these analyses, such as cosmic variance, would have on the possibility of detecting anisotropy with PTAs in the near future.

Speaker: Enrico Perboni (T (Cosmology))

The impact of cosmic variance on PTAs anisotropy searches.pdf

117 Measuring SGWB intensity and polarisation anisotropies with Pulsar Timing Arrays

Recent PTA analyses show strong evidence for a SGWB with the characteristic Hellings-Downs inter-pulsar correlations. The observed signal may stem from supermassive black hole binary mergers or early universe phenomena. These two scenarios can differ significantly in the expected level of anisotropy, which could be used to discriminate between astrophysical and cosmological origin of the signal. We assess the sensitivity of current and future SKA-like PTA experiments to intensity and circular polarisation anisotropies of kinematic origin, which are generated due to our motion w.r.t the SGWB isotropic frame and expected to be the largest anisotropies for cosmological scenarios. We also discuss the possibility of detection of circular polarisation anisotropies for the astrophysical scenario, finding them to be within the reach of near-future experiments for the expected level of circular polarisation.

Speaker: Ameek Malhotra (Swansea University)

DESY_2024_AmeekMalhotra.pdf

Parallel Thursday Pheno 1

118 Minimal decaying dark matter: from cosmological tensions to neutrino signatures

The invisible decay of cold dark matter into a slightly lighter dark sector particle on cosmological time-scales has been proposed as a solution to the $S_8$ tension. In this work we discuss the possible embedding of this scenario within a particle physics framework, and we investigate its phenomenology. We identify a minimal dark matter decay setup that addresses the $S_8$ tension, while avoiding the stringent constraints from indirect dark matter searches. In our scenario, the dark sector contains two singlet fermions $N_{1,2}$, quasi-degenerate in mass, and carrying lepton number so that the heaviest state ($N_2$) decays into the lightest ($N_1$) and two neutrinos via a higher-dimensional operator $N_2\to \bar N_1\nu\nu$. The conservation of lepton number, and the small phase-space available for the decay, forbids the decay channels into hadrons and strongly suppresses the decays into photons or charged leptons. We derive complementary constraints on the model parameters from neutrino detectors, freeze-in dark matter production via $\nu\nu\to N_1N_2$, collider experiments and blazar observations, and we show that the upcoming JUNO neutrino observatory could detect signals of dark matter decay for model parameters addressing the $S_8$ tension if the dark matter mass is below $\simeq 1$GeV.

Speaker: Lea Fuß (TUM)

DESY_Theory_Workshop_2024_Talk.pdf

119 A new solution of the Dark Matter-Baryon Coincidence

The comparable abundances of dark matter and baryons urge for an explanation that relates the dark sector to the QCD sector. In Asymmetric Dark Matter models, the number densities of both sectors are naturally similar. However, a complete solution should also include a mechanism for comparable masses. In this talk, I will present a new solution where the dark matter mass is generated by the QCD condensate, ensuring the mass is at the GeV scale. The UV completion and relevant phenomenology will also be discussed.

Speaker: Yi Chung (Max-Planck-Institut für Kernphysik)

DESY_Slide.pdf

120 Impacts of electroweak symmetry breaking on axion-like particles as dark matter

Axion-like particles (ALPs), the pseudo Nambu-goldstone bosons arising from the spontaneous breaking of global symmetry, are promising candidates for dark matter. The most extensively studied ALP production mechanism is known as the misalignment mechanism, where ALP is presumed to remain frozen at a point in the field space until it begins oscillating around the potential minimum and behaves as cold dark matter (CDM). The oscillation initiates once the universe Hubble expansion rate falls below the ALP mass, defining the oscillation frequency. Here, we examine how electroweak symmetry breaking (EWSB) affects ALP evolution, specifically through a global symmetry breaking Higgs portal operator at dimension-6. The interaction is observed to contribute partially to ALP's mass during EWSB, thus altering oscillation frequency and influencing the correlation between the scale of symmetry breaking and its mass. The novelty of this study lies in broadening the parameter space satisfying correct CDM relic density, facilitating future exploration through a diverse range of experimental avenues.

Speaker: Soumen Kumar Manna (Indian Institute of Technology Guwahati)

121 Enhancement of p-wave dark matter annihilation by quasi-bound states

In this talk we scrutinize the Sommerfeld enhancement in dark matter pair annihilation for $p$-wave and higher-$\ell$ partial waves. For the Yukawa potential these feature a super-resonant Breit-Wigner peak in their velocity-dependence close to Sommerfeld resonances as well as a universal scaling with velocity for all $\ell\geq 1$ that differs from the $s$-wave case.
We provide a quantum mechanical explanation for these phenomena in terms of quasi-bound states sustained by the centrifugal barrier of the partial-wave potential, and give approximate WKB expressions capturing the main effects. The impact of quasi-bound states is exemplified for wino dark matter and models with light mediators, with a focus on indirect detection signals.
We note that quasi-bound states also explain similar peaks in the bound-state formation and self-scattering cross sections.

Speaker: Lorenzo De Ros (TUM Technische Universität München)

Lorenzo_De_Ros_presentation.odp

Lorenzo_De_Ros_presentation.pdf

122 Boosted dark matter and their collinear splitting effects at dark matter detection experiments

I will show the collinear splitting effects of boosted dark matter at detection experiments based on simplified models. In particular, based on the dark photon model, the observation of Cosmic ray induced boosted DM at neutrino detectors with high energy thresholds will be modified by the initial state radiation(DM PDF). In addition, based on two-component DM models, the dark parton showering effects for DM indirect detection, where the heavier DM component which dominates the relic density annihilates into boosted lighter species.

Speaker: Cong Zhang (BCTP, Physics Institute, University of Bonn)

CongZhang_BDM_desy.pdf

123 The dawn of nuclear supremacy for dark matter searches — implications of the laser excitation of Th-229

The isomer transition of Th-229 has recently been excited for the first time by a VUV laser and subsequently the transition energy has been determined with a relative error of $O(10^{-6})$ (by now even $O(10^{-10})$). Due to its enhanced sensitivity to scalars coupling to the nuclear sector compared to other optical clocks, measurements of the lineshape will soon start probing uncharted parameter space as I will discuss. This is even before an optical clock based on this transition is realized.

Speaker: Wolfram Ratzinger

DESY2024-1.pdf

124 Anapole Dark Matter Direct Detection and Gravitinos

We explore direct detection constraints on the anapole form factors of massive spin-3/2 Majorana dark matter particle. From supergravity, the gravitino naturally emerges as a candidate. We calculate the anapole form factors of the LSP gravitino in N = 1 broken supergravity, analyzing their dependence on the parameters of the theory and evaluating the prospects for its direct detection.
Furthermore, the general interactions between spin-3/2 fermions and lower-spin particles are explored, revealing stringent constraints on a renormalizable realization of one-loop interactions with a photon. Based on our findings, we propose an extension to the Standard Model incorporating a dark sector with spin-3/2 dark matter. Current direct detection limits tightly constrain the parameter space of this model.

Speaker: Onur Yonar

Onur_Yonar_DESY_2024.pdf

16:00 Coffee break

125 Precision Calculations of Electroweak Phase Transitions.

We present a detailed study of the precision calculations of higher-order contributions to effective potential with the application of three-dimensional effective field theories (3D EFTs). Our work focuses on the thermodynamic quantification and description of electroweak phase transitions in the early Universe for the complex singlet extended Standard Model (cxSM). In particular, we address the issue of gauge and scale dependences associated with the effective potential, which can lead to ambiguities when calculating thermodynamical quantities from the effective potential. To overcome this issue, we employ the high temperature 3D EFT framework, which provides a robust approach for consistently taking into account the relevant contributions in physical predictions. In addition, we study the ambiguities in commonly used renormalization schemes of the effective potential. The phenomenological implications of our results are discussed.

Speaker: Maximilian Loeschner (T (Phenomenology))

Loeschner-DESY-Theory-Workshop-2024-compressed.pdf

126 Prospects for constraining light-quark electroweak couplings at Higgs factories

Electroweak Precision Measurements are stringent tests of the Standard Model and sensitive probes to New Physics. Accurate studies of the Z-boson couplings to the first-generation quarks could reveal potential discrepancies between the fundamental theory and experimental data. Future e+e- colliders offering high statistics of Z bosons would be an excellent tool to perform such a measurement based on comparison of radiative and non-radiative hadronic decays. Due to the difference in quark charge, the relative contribution of the events with final-state radiation (FSR) directly reflects the ratio of decays involving up- and down-type quarks. Such an analysis requires proper modeling and statistical discrimination between photons coming from different sources, including initial-state radiation (ISR), FSR, parton showers and hadronisation. In our contribution, we show how to extract the values of the Z couplings to light quarks and present the estimated uncertainties of the measurement.

Speaker: Krzysztof Mekala (T (Phenomenology))

Light_quarks_DESY.pdf

127 Small Instanton-Induced Flavour Invariants and the Axion Potential

Small instantons can increase the axion mass, due to an appropriate modification of QCD in the ultraviolet (UV), in a way where the axion still solves the strong CP problem. However, if any CP violation is present in UV theories where small instanton effects are enhanced, the minimum of the axion potential will be shifted, destroying the axion solution strong CP problem. In this talk, I will first introduce the use of flavour invariants to capture CP violation in the Standard Model Effective Field Theory (SMEFT). I will then show that these CP-breaking SMEFT flavour invariants naturally arise in the instanton computation of the shifted minimum of the axion potential. Finally, I will present how the invariants can be used to make statements about the way CP-violating SMEFT operators can enter in instanton computations and how the invariants provide a classification of the leading effects of all possible SMEFT operators.

Speaker: Jonathan Kley (T (Theorie))

Kley_DESYTW24.pdf

Parallel Thursday Strings & Mathematical Physics 1

128 Differential Equations for Cosmological Correlators with Massive States

In this talk, I will discuss recent advancements in calculating integrals of cosmological correlators in the de Sitter universe. I will begin by examining the case of massless scalars and how they have been recently addressed using twisted cohomology. The main focus of this talk will be on relative twisted cohomology, presenting our new results for correlators with internally massive states by utilizing the integral representation of the Bessel $K_\nu(z)$ function. Specifically, inspired by perturbative calculations of Feynman integrals, I will introduce the master integrals associated with the two-site cubic interaction at tree level involving one internal massive exchange. I will demonstrate how we obtain the "$\lambda$" factorized system of differential equations for these master integrals and their solutions. Finally, I will comment on the fully massive case, explaining its subtleties and how it can be calculated using our mathematical framework.

Speaker: Seyed Pouria Mazloumi (Uni Mainz)

DESY .pdf

129 Lining up a Positive Semi-Definite Six-Point Bootstrap

Recently, we initiated a positive semi-definite numerical bootstrap program for multi-point correlators. Considering six-point functions of operators on a line we reformulated the crossing symmetry equation for a pair of comb-channel expansions as a semi-definite programming problem. Through a combination of analytical and numerical techniques we obtained rigorous bounds on CFT data in the triple-twist channel for several examples.

Speaker: Sebastian-Philip Harris (T (Stringtheory))

DESY_Theory_Workshop__Sparsity_in_the_Numerical_Six_point_Bootstrap.pdf

130 Jet Bundle Methods for Scalar EFTs

Geometric formulations of EFTs formulate fields as coordinates on a field space manifold, which provides an alternative method of studying theories by relating physical quantities emerging from the two derivative term to geometric tensors.
Jet Bundles provide us with the tools to express any scalar Lagrangian of any derivative order in terms of a (pseudo-)Riemannian metric, thus allowing us to expand upon prior formulations by relating all physical quantities to geometric tensors on the appropriate jet bundle order. Field redefinitions and the invariance of the S-matrix find a natural description in terms of diffeomorphisms and the transformation of tensors under them.
The talk will introduce the mathematical formalism of Jet Bundles showing how they can be utilized in the context of EFTs as well as showing some examples of their applications.

Speaker: Mohammad Alminawi (University of Zurich)

DESY- Jet Bundle Methods for Scalar EFTs.pdf

131 Effective field theory in de Sitter space and the method of regions

Understanding the infrared dynamics of the massless, minimally coupled, real scalar field in de Sitter space remains an important open problem. When computed in perturbation theory, the in-in correlation functions are plagued by infrared divergences and secularly growing terms. The Soft de Sitter Effective Theory (SdSET) was developed as a framework in which these issues can be addressed. In this talk I will discuss how the Method of Regions can be applied to simplify the necessary matching computations to determine the free parameters of the SdSET and how the mentioned issues are resolved within the EFT.

Speaker: Andrea Federico Sanfilippo (Technische Universität München)

DESY2024Slides.pdf

132 Higher-Point Integrands and Ten-Dimensional Null Limits

Using twistor methods for determinant operators, we compute
integrands for correlators of external half-BPS operators of
arbitrary charges and polarizations at one and two loops and at
five and six points, in the planar limit. Collecting integrands
for all charges in a generating function, that generating
functions displays poles at ten-dimensional null limits which
effectively produce cuts in the color surface. Taking the
cyclic 10d null polygon limit cuts the color sphere into two
disks. The generating function in this limit is conjecturally
equal to the integrand of a Coulomb-branch amplitude. Isolating
this limit directly at the level of twistors, we compute the
two-loop Coulomb-branch integrand for any number of particles.

Speaker: Albert Bekov (T (Stringtheory))

talk_bekov.pdf

133 Feynman Integrals, Calabi-Yau Manifolds, and Abelian Curves

There is a surprising connection between Feyman integrals and geometry: often families of Feynman integrals are related to geometric quantities of Calabi-Yau or other manifolds. This relation makes it possible to use geometric techniques to compute the Feyman integrals, and reveals some interesting structures, both in Feynman integrals and the associated geometries. Intirguingly, it is sometimes possible to associate multiple geometries to a single Feynman integral, with each geometry providing a different point of view.

In this talk, I first give a brief overview of the connection between Feynman integrals and Calabi-Yau geometries. Then I present a novel construction of a family of Abelian curves whose periods are associated to Feynman integrals. To find such curves, we first use the connection between Feynman integrals and Calabi-Yau manifolds to express the integrals in terms of Calabi-Yau periods. Natural candidates for Abelian curves enocding these periods are then given by intermediate Jacobians, which are well-studied tori that can be associated to any Calabi-Yau manifolds. However, the classical (Griffiths and Weil) Jacobians are either Abelian or vary holomorphically, but not both, and thus do not provide a simple relation between Feynman integrals and periods. This motivates us to construct a novel type of intermediate Jacobian with both of the desirable properties. The price one has to pay is that the Jacobian is not defined everywhere in the moduli space of the Calabi-Yau manifold. However, this restriction is very natural from the amplitudes perspective: the moduli of the Calabi-Yau manifold are already restricted by conditions such as that the masses appearing in the corresponding Feynman integrals are real.

This talk is based on joint work with Jockers, Kotlewski, McLeod, Pögel, Sarve, Wang, and Weinzierl.

Speaker: Pyry Kuusela (Johannes Gutenberg University of Mainz)

Feynman_Integrals_Calabi-Yau_Manifolds_and_Abelian_Curves_DESY_2024.pdf

15:45 Coffee Break

134 Conformal line defects at finite temperature

The study of line defects in conformal field theories (CFTs) is a crucial area of research, as they describe a wide range of physical phenomena from magnetic impurities in condensed-matter systems to the radiation of moving quarks in high-energy physics. A notable class of defects, called conformal defects, breaks the conformal symmetry in a controlled way, with the residual symmetry imposing significant constraints on observables.

In this talk, I report on recent developments in the study of line defect CFTs at finite temperature. Focusing on the specific case of line defects wrapping the thermal circle, we identify the OPE data necessary to solve the correlation functions of a given model. From consistency conditions on two-point functions, we derive novel sum rules that can be used to set up a bootstrap problem. These results are illustrated for free theories and for the $O(N)$ model, where computations can be performed analytically.

Speaker: Julien Barrat (T (Stringtheory))

talk.pdf

135 Integrated correlators at strong coupling in an orbifold of N=4 SYM

We consider the 4d $\mathcal{N}=2$ superconformal quiver gauge theory obtained by a $\mathbb{Z}_2$ orbifold of $\mathcal{N}=4$ super Yang-Mills (SYM). By exploiting supersymmetric localization, we study the integrated correlator of two Coulomb branch and two moment map operators and the integrated correlator of four moment map operators, determining exact expressions valid for any value of the 't Hooft coupling in the planar limit. Additionally, for the second correlator, we obtain an exact expression also for the next-to-planar contribution. Then, we derive the leading terms of their strong-coupling expansions and outline the differences with respect to the $\mathcal{N}=4$ SYM theory.

Speaker: Mr Alessandro Pini (Humboldt University)

Alessandro Pini slides talk DESY workshop 2024.pdf

136 The Higgs Branch of minimally supersymmetric 6d SCFTs Higgsable to (2,0) theories.

The landscape of 6d SCFTs with minimal supersymmetry constitutes the perfect playground to learn about interesting aspects of SCFTs due to the many constraints that symmetries enforce. Therefore, I will discuss an intriguing class of minimal supersymmetric conformal field theories in six dimensions that under Higgs branch RG flow presents supersymmetry enhancement to the 6d $(2,0)$ SCFTs of type $D_k$ and $E_{6,7,8}$. A geometric approach, where theories are constructed as F-theory compactifications with Higgsing being equivalent to complex structure deformation of said space, will be paired with a brane construction in Type IIA with an ON$^-$ plane that allows the extraction of a magnetic unitary-orthosymplectic 3d $\mathcal{N}=4$ quiver that encodes the 6d theory Higgsable to type $D$'s Higgs branch. The combination of these different perspectives broadens our understanding of the moduli space structure: when the complex structure deformations become too hard to study, quiver subtraction (and brane dynamics) on the magnetic quiver side simplifies the problem, conversely, when the latter lacks a systematic understanding, geometry sheds light on what are the possible Higgsing patterns. I will conclude by explaining how the interplay of these toolkits makes room to extend the detailing of the Higgs branch structure, i.e. leaves and transverse slices, for theories Higgsable to type $E$ that lack both a Type IIA brane and magnetic quiver construction.

Speaker: Lorenzo Mansi (T (Stringtheory))

DESY_Workshop_Higgsable_to_D_2024-4.pdf

Hertz Lecture

19:00 Conference dinner

Friday 27 September

Plenary Sessions Friday I

Convener: Bibhushan Shakya (T (Cosmology))

137 HIgh-Frequency Gravitational Waves

Speaker: S. Ellis

S_Ellis_DESYworkshop.pdf

138 Primordial Black Holes

Speaker: G. Franciolini

GF_DESY24.pdf

139 GW / string superradiance

Speaker: A. Hook

DESY_hook.pdf

11:00 Coffee break

Plenary Sessions Friday II

Convener: Jörg Jäckel

140 Quantum Sensors

Speaker: A. Chou

achou_desy_qs_final.pdf

141 Large-scale Atom Interferometry for Fundamental Physics

Speaker: O. Buchmüller

Cold Atom Quantum Technology to Explore Fundamental Physics DESY Theory Workshop Sep 2024.pptx

Closing

Andreas Ringwald Fest

Dinner