New Perspectives in Conformal Field Theorie and Gravity

26 Sept 2023, 12:00 → 29 Sept 2023, 14:00 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.

 

 

Tuesday 26 September

12:45 → 13:45 Registration

13:45 → 13:55 Welcome

13:55 → 17:40 Plenary Session Tuesday

Convener: Johanna Erdmenger & Volker Schomerus

14:00 The Virasoro Minimal String

The last years have provided us with a number of toy models, where holography can be completely understood and even proved. I will discuss one such recent example. I will introduce a critical string theory in two dimensions and demonstrate that this theory, viewed as two-dimensional quantum gravity on the worldsheet, is equivalent to a double-scaled matrix integral, which provides the holographic description. The worldsheet theory consists of Liouville CFT with central charge c\ge 25 coupled to timelike Liouville CFT with central charge 26-c. The double-scaled matrix integral has as its leading density of states the universal Cardy density of primaries in a two-dimensional CFT, which gives the theory its name. The talk is based on joint work with Scott Collier, Beatrix Mühlmann and Victor Rodriguez.

Speaker: L. Eberhardt (IAS Princeton)

Loebbert-TalkDESYTheoryWorkshop.pdf

14:40 Twisting and untwisting in supergravity, conformal field theory, and holography

I will give a bird's-eye view of some recent developments connected to twists of supergravity theories and to the twisted holography program, trying to highlight structural features that I have found both interesting and fruitful. The focus will be on examples related to M-theory.

Speaker: I. Saberi (LMU Munich)

DESY-40min.pdf

15:20 Coffee break

15:50 Gerhard Mack in Memoriam

Speaker: Volker Schomerus & Hans Kastrup (DESY)

BackBiovs2.pdf

16:15 Black hole bulk-cone singularities

In theories with gravity duals Lorentzian correlators exhibit surprising singularities. These serve as the field-theoretic representation of the emergent bulk causal structure.
In this talk we describe the singularity structure of the thermal two-point function which captures the causal structure of its dual black hole geometry. We explain
how these singularities can be computed in the gravity approximation and discuss the effects of stringy corrections on the singular behavior.

Speaker: A. Zhiboedov (CERN)

16:55 Holographic Correlators for all Λs

In this talk we will discuss the central role of Euclidean anti-de Sitter space in defining holographic correlation functions on Lorentzian AdS, dS and flat spaces.

Speaker: C. Sleight (Durham)

DESY - Sleight.pdf

18:00 → 19:00 Reception

Wednesday 27 September

09:30 → 12:40 Plenary Session Wednesday

Convener: Jörg Teschner & Olaf Lechtenfeld

09:30 Subsystem Symmetries

Systems with subsystem symmetries have recently emerged as an important frontier in theoretical physics. They arise in novel lattice systems, describing "fractonic" phases of matter -- a generalization of topological phases. From the formal point of view, they challenge dearly held notions about what a quantum field theory is, most notably the Wilsonian paradigm. After reviewing these recent developments we'll highlight a few recent applications: symmetry breaking, interactions, foliated field theories and spacetime subsystem symmetries.

Speaker: A. Karch (U. of Texas at Austin)

DESY23.pptx

10:10 Non-relativistic gravity and non-Lorentzian geometry

I will review Newton-Cartan gravity with an emphasis on recent developments, including the covariant, off-shell large speed of light expansion of general relativity. Depending on the matter content, this expansion either leads to Newton-Cartan geometry with absolute time or to Newton-Cartan geometry with non-relativistic gravitational time dilation effects. The latter shows that non-relativistic gravity includes a strong field regime and goes beyond Newtonian gravity. Earlier work on Newton-Cartan geometry will be briefly discussed, after which we turn to modern approaches. Finally, I will mention matter couplings, solutions and odd powers in 1/c, as well as a summary of related topics. The latter includes consideration of the opposiite limit in which c is very small, along
with applications of non-Lorentzian geometry to string theory and AdS/CFT.

Speaker: N. Obers (Nordita)

10:50 Coffee break

11:20 Bootstrability in multi correlators

Speaker: N. Gromov (KCL London)

2023 Hamburg DESY.pptx

12:00 Diamonds of integrable deformations

There are two well-known origins of 2-dimensional integrable QFTs from 4 dimensions -- localisation of 4d Chern-Simons and symmetry reduction of 4d anti self-dual Yang-Mills. It is a conjecture of Costello that these can be unified in a diamond of theories, starting from holomorphic Chern-Simons theory in 6 dimensions.

It has been shown how this works for the simplest class of theories, including the principal chiral model with a Wess-Zumino term, by Bittleston and Skinner. In this talk I will discuss what happens if we try to deform and explore the new features that appear, including the role of novel boundary conditions in 4d Chern-Simons.

This talk is based on work with Lewis Cole, Ryan Cullinan, Joaquin Liniado and Dan Thompson.

Speaker: B. Hoare (Durham)

Hoare-2309-DTW_corrected.pdf

12:45 → 14:00 Lunch

14:00 → 15:30 Parallel Session Wednesday: Gravitational waves/phase transitions session

Convener: Laura Sagunski

14:00 Welcome

Information about technique, where to upload slides, informal discussion sessions

Speaker: Laura Sagunski

14:10 Higgsless simulations - A modern tool for stochastic gravitational waves from phase transitions

A stochastic gravitational wave background of cosmological origin is an intriguing possibility to be probed by gravitational wave detectors such as pulsar timing arrays and LISA in the near future. In this talk, I will present a novel “Higgsless” simulation to predict the stochastic gravitational wave spectrum from first-order phase transitions in the early universe. I will present results for weak-to-intermediate phase transitions, and demonstrate an application to phase transitions seeded by domain walls. Being numerically efficient and fully nonlinear, the “Higgsless” approach will pave the way for exploring previously uncharted regimes of strong phase transitions and relativistic wall velocities.

Speaker: Isak Stomberg (DESY)

14:30 Gravitational waves from QCD-triggered conformal symmetry breaking

Classically scale-invariant Standard Model extensions predict an intriguing thermal history of the early universe. In contrast to the common paradigm, the onset of the electroweak phase transition can be significantly delayed while the universe undergoes a period of thermal inflation. Then, a first-order QCD chiral phase transition could not only trigger electroweak symmetry breaking but also initiate the exit from supercooling. I will outline how such a scenario arises naturally in a large class of scale-invariant Standard Model extensions. Then, I will discuss how to study the transition dynamics by means of effective QCD models. Finally, the gravitational wave signal from the chiral phase transition in a supercooled universe is presented. While a large amount of latent heat is naturally involved if thermal inflation ends, a supercooling period prior to the QCD scale considerably enhances the timescale of the transition. This enhancement implies great observational prospects at future observatories.

Speaker: Daniel Schmitt

supercoolExit_DESY_v2.pdf

14:50 Gravitational waves from Dark Phase Transitions at Strong Coupling

In this talk, we demonstrate how to predict the gravitational wave spectra of Strongly coupled QFTs using holography and lattice data input for a pure SU(N) Yang-Mills theory with small uncertainties. We will elaborate on how we obtain an effective potential using holography with the free energy landscape approach and formulate an effective action. Once the effective action is in our grasp, we will use this to study bubble nucleation to predict the gravitational wave spectra. Furthermore, we will discuss how the bubble wall velocity computations can be made in steady-state configurations using holographic techniques by computations of the plasma friction force.

Speaker: Mr Nicklas Ramberg (Johannes gutenberg universität Mainz)

DESY_Theory_Ramberg_0927.pdf

15:10 Predicting dark matter and gravitational waves signals from a dark Higgs mechanism

The next generation of gravitational wave (GW) detectors open up a new window to probe
physics beyond the Standard Model in the early universe. An intriguing possibility are
first order phase transition in a dark sector giving rise to a stochastic GW background.
In this talk I will discuss GW signals from a dark sector with a spontaneously broken
gauge symmetry and a stable dark fermion. Requiring the observed relic abundance of dark
matter constrains the GW signal frequency to lie within the LISA sensitivity range.
Finally I will consider a scenario with feeble coupling between the dark and Standard
Model sector, allowing the temperatures of the two sectors to evolve independently during
the phase transition.

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

DESY_JonasMatuszak.pdf

14:00 → 15:30 Parallel Session Wednesday: Phenomenology I

14:00 Precision tests of the Standard Model in global SMEFT analyses: Fitting with a CLEW

Semileptonic charged-current (CC) interactions are crucial for exploring the nuances of the Standard Model (SM) and its possible extensions. Recent examinations have underscored discrepancies with the SM predictions, particularly in the Cabibbo Angle Anomaly (CAA), which demonstrates a 3$\sigma$ deviation from zero. In this paper, we undertake a rigorous analysis using the SMEFT framework to shed light on potential BSM sources of the CAA. By integrating insights from collider processes ("C"), low-energy CC processes ("L"), and electroweak precision observables ("EW"), we introduce a holistic "CLEW" approach. Our analysis underscores the significance of a global CLEW perspective in vetting BSM propositions that align with observations across scales, from the weak to the TeV range. While our initial impetus revolves around the CAA, our findings naturally establish a foundational CLEW framework, poised to significantly influence future SMEFT investigations, especially those sidelining severe phenomenological constraints, including FCNCs and CP violations. We will touch upon preliminary results within the ambit of the $U(3)^5$ flavor assumption, followed by an in-depth exploration of a "flavor-assumption-independent" analysis. In this broader analysis, we have incorporated the Akaike Information Criterion (AIC). When combined with the $\chi^2$ method, the AIC promotes a model that not only aligns well with experimental data but also circumvents unnecessary complexities, accentuating the challenges and prospective avenues for model-independent global analyses.

Speaker: Tom Tong (Universität Siegen)

CLEW.pdf

14:22 One-loop IR/UV dictionary in the SMEFT

Effective field theories offer a rationale for the classification of heavy new physics models based on the size of their contribution to the effective Lagrangian and therefore to experimental observables. When trying to connect theory with experiment, dictionaries which relate possible UV scenarios with the relevant effective interactions are of utmost importance.
In this talk, I will report on the first step towards the calculation of the one-loop, dimension 6 IR/UV dictionary in the SMEFT. We consider dimension-six operators in the SMEFT that cannot be generated at tree-level in weakly-coupled extensions of the Standard Model, meaning that their leading contribution arises at one-loop. These correspond to operators with field strength tensors, all of which can have important phenomenological consequences. We provide a complete classification of renormalizable extensions of the Standard Model with new scalar and fermion fields that contribute to these operators at one-loop order, together with their explicit contribution. These results are encoded in a Mathematica package called SOLD.

Speaker: Guilherme Luis de Sousa Fialho Guedes (T (Phenomenology))

DESY_TheoryWorkshop23.pdf

14:44 Searching for U(2) New Physics with Flavour, Electroweak, and Collider Data

TeV-scale new physics is generally very constrained by a plethora of measurements at different energy scales, ranging from flavour observables to the LHC's proton-proton collisions, with stronger bounds typically associated with fermions of the first two generations and with flavour-changing transitions.
It is therefore clear that any such low-scale new physics requires an organising principle regarding the flavour structure of its couplings.
In this context, the U(2) paradigm has received a lot of attention in the past decade, also due to its possible connection with the flavour puzzle and the Higgs hierarchy problem.
In a model-independent approach, we consider the SMEFT at dimension six, which has 124 independent structures in the exact U(2) limit.
Under this assumption, we study the constraints on all the operators coming from flavour, Electroweak precision tests as well as collider data, including effects arising from resummed RGE.
We identify the most stringent bounds in each case, and the overall conditions U(2)-symmetric new physics must satisfy in order to live in the few TeV range, discussing also future projections for the FCC-ee Z-pole run.

Speaker: Lukas Allwicher (University of Zurich)

desy_23_allwicher.pdf

15:06 Higgs pair production at the LHC in the 2HDM

Probing the Higgs potential through the measurement of the trilinear Higgs coupling is one of the main goals of particle physics. Large deviations from the Standard Model (SM) prediction can be accommodated in models with extended Higgs sectors while being in agreement with all existing experimental and theoretical constraints. In the framework of the Two Higgs Doublet Model, we study the potential sensitivity to the SM-like trilinear Higgs coupling and the BSM triple Higgs coupling involving a resonantly produced CP-even heavier Higgs boson. For this purpose, we analyze the theoretical prediction of the total Higgs pair production cross section and the invariant mass distribution of two SM-like Higgses in the final state at the LHC. We show that the inclusion of loop corrections to the trilinear Higgs coupling is crucial to exclude regions of otherwise unconstrained parameter space. Finally, we discuss the applicability of resonant and non-resonant Higgs pair production experimental limits for testing the predictions of extended Higgs sectors.

Speaker: Kateryna Radchenko Serdula (T (Phenomenology))

DESY_Theory_Radchenko.pdf

14:00 → 15:30 Parallel Session Wednesday: Strings / Mathematicals Physics I

Convener: Craig Lawrie (T (Theorie))

14:00 Vacua of gauged N=2 supergravities arising as special subloci of the complex structure moduli space of String Compactifications

Part of the moduli space of type II string compactifications on Calabi-Yau threefolds is characterized by the variation of Hodge structure of the complex structure moduli space of the Calabi-Yau threefold.
In this talk, we will discuss subspaces of the complex structure moduli space, which are realized in terms of a closed variation of sub-Hodge structures. Physically, such sub-Hodge structures give rise to Minkowski-vacua of the associated gauged N=2 supergravity theory. We will illustrate these concepts with concrete examples of 2-parameter moduli spaces of Calabi-Yau threefolds.

Speaker: Sören Kotlewski

Vacua of gauged N=2 supergravities arising as special subloci of the complex structure moduli space of String Compactifications.pdf

14:18 Physics and Modularity of Calabi-Yau Manifolds

One of the most fascinating and important topics in contemporary mathematics is the study of modularity. This is a phenomenon where it is possible to associate a modular form to a manifold by using its number theoretic properties. Surprisingly, this deep correspondence has concrete implications for the physics of Calabi-Yau compactifications of string theory; the modular form turns out to encode physical information. For instance, it appears in the Bekenstein-Hawking entropy of BPS black holes. Another central example is given by IIB flux compactifications, where the modular form specifies the axiodilaton, or equivalently F-theory fibre in the F-theory uplift.

In this talk, I give a concise overview of the geometry and number theory behind modularity, as well as various instances in physics where modularity appears. I will then explain in concrete terms, how modular Calabi-Yau manifolds can be found in practice, and how their modular properties can be studied by using numerical methods. Additionally, I will present some examples where results and conjectures from number theory give novel approaches to solving significant problems in physics.

This talk is based on several joint works with Candelas, de la Ossa, Jockers, Kotlewski, and McGovern.

Speaker: Pyry Kuusela (Johannes Gutenberg University of Mainz)

Physics_and_CY_Modularity_DESY_2023.pdf

14:36 Superconformal algebras for (twisted) connected sums

The worldsheet conformal field theory associated to a string compactification is intimately related to the geometry of the underlying compact manifold. In this talk we will explore compactifications on manifolds that can be constructed as a (twisted) connected sum of two open manifolds. At the level of chiral algebras we expect the geometric structure to give rise to a "diamond" of algebra inclusions, and automorphisms of these algebras can be interpreted as candidates for mirror maps on the compact manifold. We will focus on the Schoen Calabi-Yau manifold and, time permitting, we will discuss further examples of holonomy G$_2$ and Spin(7). This talk is based on [2306.14798] as well as joint work with M.-A. Fiset, [2104.05716].

Speaker: Mateo Galdeano (TUHH (Technische Universitaet Hamburg-Harburg))

Galdeano-DESYtheory23.pdf

14:54 (Higher-)spinning at the Edge of the Swampland

The study of low-energy theories that can be embedded into string theory has led to a number of proposals about the nature of quantum gravity. In turn, these ideas have implications for conformal field theories through holography. For instance, the CFT Distance Conjecture posits that at infinite-distance points of a conformal manifold, there is an infinite tower of conserved higher-spin currents, indicating that a sector of the CFT becomes free, and vice versa. I will argue that under a natural set of assumptions, such as unitarity and the existence of a stress-energy tensor but without requiring the presence of supersymmetry, it is possible to prove that all points with such a tower of higher-spin currents are at infinite distance.

Speaker: Florent Baume (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

Florent_Baume-desy-workshop-2023-09.pdf

15:12 The Higgs Branch of Heterotic LSTs Hasse Diagrams and Generalized Symmetries

We investigate the Higgs Branch of the six dimensional $\mathcal{N}=(1,0)$ Little String Theories models corresponding to the worldvolume of Heterotic $E_8 \times E_8$ and their T-dual $\mathrm{Spin}(32)/\mathbb{Z_2}$ instantons. Relying on the magnetic quiver technique, we manage to extract a $3d$ $\mathcal{N}=4$ quiver whose Coulomb Branch moduli space is the same of the Higgs Branch of the six dimensional theory. Therefore, applying the Quiver Subtraction algorithm we engineer the Hasse diagram associated to the Higgs Branch RG flow of the considered LST models, and check that it matches with the F-theory prediction. We propose an algorithm to match T-dual models by keeping tracks of the 2-group structure constant $\hat{\kappa}$ along Higgs branch RG flows starting from parent dual models.

Speaker: Lorenzo Mansi (T (Stringtheory))

Higgs_LSTs.pdf

14:00 → 15:30 Parallel Session Wednesday: Strings / Mathematicals Physics III

Convener: Anne Spiering (Trinity College Dublin)

14:00 The cusp anomalous dimension of ABJM from a Thermodynamic Bethe Ansatz approach

Since the early days of the AdS/CFT correspondence, integrability has proven to be a powerful tool for the study of the spectral problem in both sides of the duality. A well-known example of this was given ten years ago by a Thermodynamic Bethe Ansatz (TBA) computation of the cusp anomalous dimension of ${\cal N}$=4 super Yang-Mills. This result naturally posed the question of whether similar ideas could be applied to other theories with holographic duals. In this talk I will present the results of arXiv:2304.01924, where we studied a TBA-based computation of the cusp anomalous dimension of the ABJM theory. We showed that in ABJM the insertions along a 1/2 BPS Wilson line are described by an integrable open spin chain, and we reproduced the one-loop cusp anomalous dimension of the theory from a Y-system approach.

Speaker: Martin Lagares (National University of La Plata)

Talk DESY-Martín Lagares.pdf

14:18 Hidden symmetries in $\mathcal{N}=2$ SCFTs

4D $\mathcal{N}=2$ SCFTs obtained from orbifolding $\mathcal{N}=4$ SYM and then performing a marginal deformation exhibit hidden symmetries. Namely, the orbifolding procedure breaks some actions of the generators coming from the parent $\mathcal{N}=4$ SYM. However, by employing a non-trivial co-product, the actions of the broken generators can be ``restored'' as generators of a hidden symmetry. In my talk I will focus on the particular example of the R-symmetry group of the $\mathbb{Z}_2$ quiver theory $SU(N) \times SU(N)$ in order to demonstrate some novel features of such symmetries. In particular, the hidden symmetry exhibited by this model allows one to relate $\frac{1}{2}$-BPS states of the $\mathcal{N}=2$ SCFTs multiplets reminiscent of $\mathcal{N}=4$ SYM.

Speaker: Hanno Bertle (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

DESY_Theory_Workshop_2023_HB.pdf

14:36 Integrability in non-relativistic string theory

Integrability has played a huge role in understanding string theory in AdS$_5 \times$S$^5$. This has motivated people to explore if integrability techniques can be applied to more general backgrounds. One of these cases is the non-relativistic limit of AdS$_5 \times$S$^5$. In this talk, I will report on recent progress in understanding classical integrable structures present in non-relativistic string theory propagating in string Newton-Cartan AdS$_5 \times$S$^5$. In particular, I will discuss classical solutions, the coset construction of the action, the Lax connection and the classical spectral curve.

Speaker: Juan Miguel Nieto Garcia (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

Non_relativistic_talk.pdf

14:54 Twist noncommutative gauge theories

Applying the Yang-Baxter (YB) deformations to the famously integrable $AdS_5\times S^5$ string give rise to a variety of new integrable models. In the context of the AdS/CFT correspondence, these models are conjectured to be dual to gauge theories on various noncommutative spacetimes obtained via Drinfel’d twists. To date, however, it was unclear how to formulate such noncommutative gauge theories precisely beyond the simplest case of constant noncommutativity. In my talk, I will show how to construct gauge invariant noncommutative Yang-Mills actions for a broad class of noncommutative structures, relying on deformed version of the Hodge star operation. I will also show how to include matter fields and hence how to construct noncommutative versions of $\mathcal{N}=4$ SYM which give promising candidates for the dual theory to YB deformations of the $AdS_5\times S^5$ string. Finally, I will elaborate on how to relate between planar Feynman diagrams of the noncommutative theory and their commutative counterparts, as the first step towards calculating the planar one loop 2-point functions of gauge invariant operators in twist noncommutative SYM.

Speaker: Tim Meier (Humboldt-Universität zu Berlin)

HamburgTalk.pdf

15:12 Coordinate Bethe Ansatz for N=2 SCFTs

The study of spin chains which capture the spectral problem of N=2 SCFTs in the planar limit can shed light on the integrability of 4d gauge theories with less supersymmetry. I investigate the SU(2) subsector of an orbifold daughter of N=4 SYM by using coordinate Bethe Ansatz method. Exact results of the coordinate Bethe ansatz hints an underlying structure such that S-matrix coefficients factorizes and this factorization is closely related to N=4 SYM spin chains in planar limit.

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

desy_theory_workshop2_deniz_bozkurt (2).pdf

15:30 → 16:00 Coffee break

16:00 → 17:30 Parallel Session Wednesday: Gravitational waves/phase transitions session

Convener: Laura Sagunski

16:00 On Particle Production from Phase Transition Bubbles

While first order phase transitions (FOPTs) have been extensively studied as promising cosmological sources of gravitational waves, the phenomenon of particle production from the expansion and collision of bubbles has received relatively little attention in the literature. Previous works have only considered semi-analytical estimates of this effect in simplified settings and have therefore left out interesting aspects. In this talk, I will discuss our improved numerical studies of particle production efficiency from more realistic scalar field configurations, revealing important qualitative details, such as the concurrence of a power law spectrum from the expansion phase and a peak from the post-collision scalar field oscillations, respectively. Our results provide easy-to-use analytic formulae that can be applied to calculate particle production in generic FOPT setups and beyond the Standard Model scenarios.

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

HendaMansour-ParticleProduction.pdf

16:20 Induced gravitational waves and baryon asymmetry fluctuations from primordial black hole formation

We consider black hole formation due to the gravitational collapse produced by large density fluctuations during an epoch of reheating with a stiff equation of state, and calculate the corresponding signal in the induced gravitational wave spectrum. By considering the existing Big Bang nucleosynthesis and CMB bounds on the total energy density of gravitational waves today, we find the corresponding constraints on the parameter space of this scenario. We also calculate the lepton asymmetry generated at the perturbative level via the chiral gravitational anomaly present in the Standard Model and find that, once this is converted to a baryon asymmetry via electroweak sphaleron processes, the large spectrum of scalar perturbations responsible for black hole formation induces an enhancement in the baryon asymmetry fluctuations on small scales.

Speaker: Julian Rey (DESY)

Baryogenesis_Presentation.pdf

16:40 The warm inflation scalar power spectrum

Inflation

Speaker: Alejandro Perez

desy_tw_APR.pdf

17:00 Inflection point inflation in SuperGravity

We study the inflection point inflation generated by polynomial superpotential and canonical K\"ahler potential under the supergravity framework, where only one chiral superfield is needed. We find the special form of the scalar potential limits the possible Hubble value up to $\mathcal{O}(10^{10}) \, \textrm{GeV}$ and the inflaton mass to $\mathcal{O}(10^{11}) \, \textrm{GeV}$. We obtained analytic results for samll field cases and present numerical results for large field ones. We find the tensor to scalar ratio $r$ is always suppressed in these models while the running of spectral index $\alpha$ will be testable in next generation CMB experiments. We also discuss the possible effects of SUSY breaking polonyi term presenting in the super potential. We find a general upper bound for SUSY breaking scale for a given Hubble value.

Speaker: Wenbin Zhao (BCTP, Uni.Bonn)

DESY23WenbinZhao.pdf

17:20 Informal discussion session

16:00 → 17:30 Parallel Session Wednesday: Phenomenology II

16:00 An Effective Approach for Axion Wormholes

Euclidean wormholes that arise in axion theories imply important phenomenological consequences in the context of the axion quality problem. In this work, we present an effective approach providing an analytic solution describing the structure of these axion wormholes. We identify the energy scales associated inside and outside the wormhole as the UV and IR regime of the wormhole respectively, which allows us to obtain the analytic structure for both the field-dependent wormhole action and its corresponding Peccei-Quinn violating operators applicable to a wide class of axion theories. We also give explicit examples that implement this approach, with some further implications and prospects.

Speaker: Dhong Yeon Cheong (Yonsei University & CERN)

DESY_2023_DYCHEONG_full.pdf

16:22 Radiative neutrino masses and the Cohen–Kaplan–Nelson bound

Cohen, Kaplan and Nelson (CKN) have argued that quantum field theories coupled to gravity feature not only a UV cutoff but also an IR cutoff, and that these cutoffs are related via the physics of black holes. By imposing that quantum field theory cannot describe black holes, they derived the relationship $\Lambda_{I R} \geq \Lambda_{U V}^{2}/M_{P}$ and therefore provide the allowed energy range for a QFT from $\Lambda_{IR}$ to $\Lambda_{UV}$. This has interesting phenomenological consequences as the cutoffs affect the calculation of loop integrals and therefore have impact on radiative corrections.

In this talk we investigate the possible impact of the CKN bound on four different radiative neutrino mass models and show that this effect has significant consequences for the parameter space.

Speaker: Patrick Adolf (TU Dortmund)

DESY23_PA.pdf

16:44 Investigating the Higgs self-couplings through triple Higgs production

Experimental information on the trilinear Higgs boson self-coupling $\kappa_3$ and the quartic self-coupling $\kappa_4$ will be crucial for gaining insight into the shape of the Higgs potential and the nature of the electroweak phase transition. While Higgs pair production processes provide access to $\kappa_3$, triple Higgs production processes, despite their small cross sections, will provide valuable complementary information on $\kappa_3$ and first experimental constraints on $\kappa_4$. In this work, we consider triple Higgs production at the HL-LHC, employing efficient Graph Neural Network methodologies to maximise the statistical yield. We show that it will be possible to establish bounds on the variation of both couplings from the HL-LHC analyses that significantly go beyond the constraints from perturbative unitarity. We also discuss the prospects for the analysis of triple Higgs production at future high-energy lepton colliders operating at the TeV scale.

Speaker: Panagiotis Stylianou (T (Phenomenology))

PanagiotisStylianou_DesyTheoryWorkshop.pdf

16:00 → 17:48 Parallel Session Wednesday: Strings / Mathematicals Physics II

Convener: Craig Lawrie (T (Theorie))

16:00 Comments on Non-invertible Symmetries in Argyres-Douglas Theories

I briefly demonstrate the presence of non-invertible symmetries in an infinite family of superconformal Argyres-Douglas theories. This class of theories arises from diagonal gauging of the flavor symmetry of a collection of multiple copies of $D_p(SU(N))$ theories. The same set of theories that we study can also be realized from 6d $\mathcal{N}=(1,0)$ compactification on a torus. The main example in this class is the $(A_2,D_4)$ theory. We show in detail that this specific theory bears the same structures of non-invertible duality and triality defects as those of $\mathcal{N}=4$ super Yang-Mills with gauge algebra 𝔰𝔲(2). The result can be extended to infinitely many other Argyres-Douglas theories in the same family, including those with central charges $a=c$ whose conformal manifold is one dimensional, and those with $a\neq c$ whose conformal manifold has dimension larger than one. Our result is supported by examining certain special cases that can be realized in terms of theories of class $\mathcal{S}$.

Speaker: Dr Alessandro Mininno (Universitat Hamburg - UHH)

DESY_AD_slides-1.pdf

16:18 Semi-stable Degenerations and the Distance Conjecture in F-theory

We analyze infinite-distance limits in the complex structure moduli space of six-dimensional F-theory, giving an algebro-geometric classification and a physical interpretation. From the point of view of the Swampland Program, the motivation is to understand the fate of open-moduli infinite-distance limits in relation with the Distance Conjecture. From an F-theory perspective, the infinite-distance limits correspond to suitable non-minimal singularities in codimension one and higher. While codimension-two finite-distance non-minimal singularities have been understood as SCFTs in a major classification effort, the goal of our analysis is to elucidate the meaning of the infinite-distance codimension-one and codimension-two non-minimal singularities. We argue that they are either decompactification or emergent string limits in a dual sense.

Speaker: Rafael Alvarez Garcia (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

Semi-stable Degenerations and the Distance Conjecture in F-theory.pdf

16:36 Understanding the tower weak gravity conjecture

The weak gravity conjecture claims that a consistent quantum gravity theory must include states, called super-extremal states, whose gauge forces mediate interactions stronger than gravity. A stronger variant of this conjecture is the tower weak gravity conjecture (tWGC), which predicts an infinite tower of super-extremal states in every direction of the charge lattice of the theory under consideration. Albeit there are several non-trivial checks in favour of the tWGC in various string theory settings in the literature, we find a set of F-theory/M-theory constructions in which such an infinite tower of super-extremal states does not seem to be present. However, we argue that fulfilling the tWGC is not always necessary and elaborate on a set of criteria to explain under which circumstances the tWGC is required.

Speaker: Cesar Fierro Cota (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

DESYTheoryWorkshopTWGC.pdf

16:55 Aspects of Flat-Space Holography and Higher Spins

The Holographic Principle considerably contributed to our understanding of quantum gravity, information theory and strongly coupled systems over the last few decades. Although its best-studied realisation arguably lies within the AdS/CFT correspondence, it is expected to apply in much more general circumstances. Of particular interest may be holographic dualities that involve gravity duals relevant for real-world scenarios, such as de Sitter or flat spacetimes.
In my talk I plan to discuss some of the peculiarities that arise in Flat-Space Holography that are not present in AdS/CFT, with particular focus on the case of three spacetime dimensions in the bulk. I will furthermore present an algebraic approach to higher-spin theory in flat spacetimes that can be utilised to introduce massive fields to the gravitational theory.

Speaker: Michel Pannier (FSU Jena)

230927_Hamburg.pdf

17:13 Pure spinor techniques in (twisted) supergravity

The pure spinor superfield formalism gives a systematic and geometric
technique to construct supersymmetric field theories from
algebro-geometric input data. Crucially, this procedure provides
superfield descriptions where the actions of the supersymmetries is
strict and which are compatible with twisting. In this talk, I will
demonstrate the merits of the formalism using the example of
eleven-dimensional supergravity. In particular, I present a uniform
construction of the interacting theory and all its twists realizing them
as generalizations of Poisson--Chern--Simons theory. In addition to
simplifying the computation of twists immensely, this also sheds some
new light on the supergeometric origin of the supergravity theory. The
talk is based on joint work with Ingmar Saberi.

Speaker: Fabian Hahner

pure-spinor-sugra-desy.pdf

16:00 → 17:30 Parallel Session Wednesday: Strings / Mathematicals Physics IV

Convener: Anne Spiering (Trinity College Dublin)

16:00 Broken global symmetries and defect conformal manifolds

I will present the collaborative work arXiv:2203.17157 with Nadav Drukker and Georgios Sakkas. Defects that break the global symmetry group provide some exactly marginal defect operators, which allow to deform a CFT along the defect conformal manifold, which is the symmetry breaking coset. Its Zamolodchikov metric is expressed as the 2-pt function of the exactly marginal operators and the Riemann tensors can be expressed as integrated 4-pt functions. We examine in detail the case of the 1/2 BPS Maldacena-Wilson loop in $\mathcal{N} = 4$ SYM, the 1/2 BPS surface operator of the 6d $\mathcal{N} = (2, 0)$ theory, the 1/2 BPS Fermionic Wilson loop in ABJM, and the magnetic line in the $O(N)$ model.

Speaker: Ziwen Kong

Talkslides_ZiwenKong.pdf

16:18 Ground state energy of the twisted AdS3 × S3 × T4 superstring and the TBA

In the present work we address the Thermodynamic Bethe Ansatz and ground state energy of the $ AdS_3 \times S_3 \times T_4 $ model from the associated mirror superstring model in the pure RR background. Independently, we show complete consistency with wrapping interaction formalism and derive generalised Lüscher expression for GSE. We prove that the underlying mirror $ Y $-system becomes solvable in various parametric regimes of the lightcone superstring theory. Moreover the contribution of the gapless worldsheet excitations coming from the $ T_4 $ can be computed exactly. Next we implement the lightcone $ AdS_3 \times S_3 \times T_4 $ superstring sigma model with twisted boundary conditions on the fields. It then allows us to find the ground state energy in the semi-classical approximation, where string tension $ h $ and lightcone momentum $ L $ are infinite (fixed ratio). Comparison of semi-classical results demonstrates that there is a full agreement with the computation from $ AdS_3 $ TBA. We also emphasize the massless factor discrepancy with respect to the initial conjecture arXiv:2112.08898 and show that it is related to the $ Y $-functions and analytic structure describing massless modes. We also make a mixed flux proposal from the TBA and find complete correspondence with the computation from the $ AdS_3 \times S_3 \times S_3 \times S_1 $ lightcone superstring. Based on arXiv:2305.17128 and upcoming work.

Speaker: Dr Anton Pribytok (Humboldt University)

AdS3_TBA_GSE.pdf

16:36 Constraints of Superconformal Symmetry

Due to their importance in both, AdS/CFT-correspondence as well as scattering amplitude research, half-BPS correlators of $\mathcal{N}=4$ SYM have experienced a tremendous amount of study in the past years.\
Especially 4- and higher point correlators are of huge interest given that, via the OPE, etc. they contain a wealth of CFT data, also for more complex operators. Despite their importance, very little is known about 5- and higher point correlators.\
In this talk, we will present a method to constrain those higher point correlators further (to be specified later).

Speaker: Ms Sophie Müller

Talk Understanding Constraints of Superconformal Symmetry.pdf

16:54 Advances in finite temperature conformal field theories

We are exploring the application of tools from Conformal Field Theories (CFTs) and (conformal) bootstrap to investigate Thermal CFTs. These theories, despite being non-critical, retain many fundamental structures of zero-temperature CFTs, such as the Operator Product Expansion, and maintain an identical conformal spectrum. However, one-point functions at finite temperature can be non zero and therefore new data (not present at zero temperature) are needed to compute correlation functions.
To delve into the study of thermal effects, we consider the theory on the "thermal" manifold S^1xR^(d-1). In this context, we present our findings based on recent work (arXiv:2306.12417) and ongoing research.

Speaker: Alessio Miscioscia (T (Stringtheory))

Miscioscia Thermal CFT.pdf

17:12 Holographic Schwinger-Keldysh Contours and Effective Actions for Fluids

In this talk, I will discuss the real-time dynamics of gravitons and photon fluctuations around the AdS-Reissner-Nordstrom black hole and argue that the dynamics of these modes are captured by a set of designer scalars in the background geometry. I will show how it is possible to isolate the phonon mode, momentum, and charge diffusion modes, and identify the combination of currents that corresponds to each of them. Using these results I will obtain the real-time Gaussian effective action, which includes both the retarded response and the associated stochastic. Finally, I will discuss possible extensions beyond linear response.

Speaker: Julio Virrueta (Friedrich-Schiller-Universität)

JVDesy2023.pdf

Thursday 28 September

09:30 → 12:45 Plenary Session Thursday

Convener: Johannes Walcher

09:30 Cosmological Correlators at Finite Coupling

Speaker: S. Komatsu (CERN)

DESYKomatsu.pdf

10:10 Feynman Integrals from Integrability and Geometry

A bottle neck for precision calculations in collider or gravitational wave physics is the computation of Feynman integrals. Here recent findings at higher loop orders emphasize the need for a deeper understanding of special functions. In this talk we highlight the family of conformal fishnet integrals as a rich setup for making progress on this frontier. In particular, we demonstrate the applicability of tools from Calabi-Yau geometry as well as AdS/CFT integrability. As an explicit example we report on recent progress for multi-loop Feynman integrals in two spacetime dimensions, where we elaborate on the connection between Calabi-Yau geometry and the so-called Basso-Dixon formula. While the restriction to two dimensions is convenient for analyzing these structures, we emphasize that higher dimensional integrals show similar features.

Speaker: F. Loebbert (U. Bonn)

10:50 Coffee break

11:20 Extrapolate Dictionaries in Celestial CFT and Conformal Collider Physics

Speaker: S. Pasterski (PI Waterloo)

Pasterski_DESY.pdf

12:00 Correlated spin systems: a tensor networkapproach

Speaker: F. Verstraete (U. Cambridge)

Verstraete_Hamburg_DESY_28_09_23.pdf

12:50 → 13:50 Lunch

13:50 → 15:20 Parallel Session Thursday: Strings / Mathematical Physics III

Convener: Anne Spiering (Trinity College Dublin)

13:50 Finite Amplitudes from a Deformed Amplituhedron Geometry

The Amplituhedron provides, via geometric means, the all-loop integrand of scattering amplitudes in maximally supersymmetric Yang-Mills theory. Unfortunately, dimensional regularization, used conventionally for integration, breaks the beautiful geometric picture. This motivates us to propose a `deformed' Amplituhedron. Focusing on the four-particle amplitude, we introduce two deformation parameters. The deformed amplitude is infrared finite, making the answer well-defined in four dimensions. Leveraging four-dimensional integration techniques based on differential equations, we compute the amplitude up to two loops. In the limit where the deformation parameters are taken to zero, we recover the known Bern-Dixon-Smirnov amplitude.
In the limit where only one deformation parameter is taken to zero, we find a connection to the angle-dependent cusp anomalous dimension.

Speaker: Wojciech Flieger (Max Planck Institute for Physics)

DESY_workshop_2023_Flieger.pdf

14:08 Symbol Alphabets from the Landau Singular Locus

We provide evidence through two loops, that rational letters of polylogarithmic Feynman integrals are captured by the Landau equations, when the latter are recast as a polynomial of the kinematic variables of the integral, known as the principal $A$-determinant. Focusing on one loop, we further show that all square-root letters may also be obtained, by re-factorizing the principal $A$-determinant with the help of Jacobi identities. We verify our findings by explicitly constructing canonical differential equations for the one-loop integrals in both odd and even dimensions of loop momenta, also finding agreement with earlier results in the literature for the latter case. At two loops, we find previously unknown solutions to the Landau equations that have non-trivial representation in the principal $A$-determinant. We argue that these new singularities are a part of the symbol alphabet at two loops.

Speaker: Felix Tellander (T (Stringtheory))

DESY_Theory_Workshop_2023.pdf

14:26 The Lion, the Witch, and the Wormhole: Ensemble averaging the symmetric product orbifold

We consider the ensemble average of two dimensional symmetric product orbifold CFTs $\text{Sym}^N(\mathbb{T}^D)$ over the Narain moduli space. We argue for a bulk dual given by $N$ copies of an abelian Chern-Simons theory coupled to topological gravity, endowed with a discrete gauge symmetry exchanging the $N$ copies. As a check of this proposal, we calculate the ensemble average of various partition and correlation functions of the symmetric product orbifold theory and compare the resulting expressions to gauge theory quantities in the bulk. We comment on the ensemble average of the tensionless string partition function on $\text{AdS}_3 \times \text{S}^3 \times \mathbb T^4$ by considering the specific case of $D=4$ with the addition of supersymmetry.

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

KanargiasDESY2023.pdf

14:44 Aspects of Four Point One Loop Superstring Amplitudes in Celestial Holography

Celestial holography is a candidate for flat space holography. Scattering amplitudes of massless particles in the bulk four dimensional Minkowski spacetime can be mapped to correlators in a putative two dimensional conformal field theory living on the celestial sphere via Mellin transform.

In 1806.05688 string tree level amplitudes have been cast into their celestial form. In it, the authors displayed some intriguing features of celestial string amplitudes including that the $\alpha' $-dependance is limited to an overall factor as opposed to being present at different powers as an expansion parameter like in regular string scattering amplitudes. Additionally, they argued that in a special limit the string world-sheet can be interpreted as the celestial sphere itself. This observation gives credence to the idea that there might be a string theoretic top-down construction for flat space holography.

Motivated by this, an obvious next step is to try to generalize this analysis to one-loop order. The first step towards this goal was taken in 2307.03551. I will present results of ongoing work using two different approaches that extend this analysis. I will show that the $\alpha' $-dependance is a persistent feature of celestial (loop) amplitudes and reproduce the known $\alpha' ^{\beta-3}$ prefactor in both approaches. Using one approach, I will give a formula for the celestial open one-loop superstring amplitude expressed in terms of powers of the conformal cross ratio. Using the other approach, I will show that the Nielsen Polylogarithm structure found in 1806.05688 at tree level, persists at loop level. An explicit formula of the planar amplitude in the forward limit below the threshold energy of massive string excitations will be presented.

Speaker: Daniel Bockisch (LMU Munich)

DESYCelestialOneLoopPresentation.pdf

15:02 Causality Criteria from Stability Analysis at Ultra-High Boost

In this work, we have exclusively employed linear stability analysis at ultra-high boost on two well-known stable-causal theories - second-order MIS and first-order BDNK, to identify the region of parameter space over which they are frame-invariantly stable and obey causal signal propagation. It has been shown that at near-luminal boost, stability criteria alone can provide the causality constraints on transport coefficients, which are identical to the asymptotic causality conditions,
without actually going to the asymptotic limit of the theories. Thus, we present an alternative approach to derive the causality constraints, which is more appropriate for low-energy effective theories like relativistic hydrodynamics.

Speaker: Shuvayu Roy (NISER)

Hamburg Shuvayu.pdf

13:50 → 15:20 Parallel Session Thursday: Strings / Mathematicals Physics I

Convener: Craig Lawrie (T (Theorie))

13:50 A (twist) gap in our knowledge of 2d CFT

I will discuss the recent construction of a family of 2d CFTs which are unitary, compact and irrational, with only Virasoro symmetry. These are the first robustly studied examples of c>1 2d CFTs with a gap in the twist of Virasoro primaries, which is a standard axiom used in deriving many universal properties of 2d CFTs.
Based on 2211.16503 and WIP with Connor Behan.

Speaker: Antonio Leite Antunes (T (Stringtheory))

Antunes.pdf

14:08 Analytic bootstrap for defect CFTs

A powerful way to study Conformal Field Theories analytically is the Lorentzian inversion formula, which allows to extract the CFT data of a given four-point function from its double discontinuity. One can also derive a dispersion relation that reconstructs directly the full correlator from the same double discontinuity. I will consider the generalisation of these methods to defect CFTs, discussing a recently derived dispersion relation that allows to compute the two-point functions of bulk operators in presence of a defect. I will show an application of this formalism to the O(N) model in the presence of a magnetic line defect, and to the case of a line defect representing a spin impurity.

Speaker: Davide Bonomi (City, University of London)

desy23_bonomi.pdf

14:26 Fermionic CFTs across dimensions

Yukawa models have been suggested to capture a wide array of condensed-matter systems that exhibit emergent Lorentz symmetry. A notable example is the case of graphene sheets, three-dimensional systems described by fermionic theories at the critical point. Graphene undergoes a second-order phase transition structurally very similar to the weak sector of the Standard Model, and this resemblance has led to the hope that it could mimic various effects of chiral and spontaneous symmetry breaking.
In this talk, I will share recent findings regarding four-point functions of two scalars and two fermions in these models. The non-perturbative structure of these correlators has been analyzed, and for the case of Yukawa CFTs with $O(N)$ symmetry we calculated them perturbatively in the context of the $\varepsilon$-expansion. The results presented here are particularly relevant for conformal bootstrap applications.

Speaker: Julien Barrat (Humboldt-Universität zu Berlin)

talk.pdf

14:44 Line defects in O(N) and Yukawa CFTs

Line defects are an example of extended objects in QFTs and CFTs, describing a plethora of interesting physics such as magnetic impurities, Wilson lines, and brane physics. They provide access to new observables and conformal data, and are important in the study of confinement and generalized symmetries.

I will discuss recent work in which we explore conformal line defects, preserving one-dimensional conformal symmetry on the defect. Using the epsilon expansion and the numerical conformal bootstrap in a complementary way allows us to study several types of conformal line defects. In particular, we focus on a localized magnetic field line defect in the O(N) CFTs and the Yukawa CFTs, which can be captured in a single framework. Using the numerical bootstrap, we found a series of intriguing cusps which we will further investigate.

Speaker: Philine Julia van Vliet (T (Stringtheory))

line_defects_on_yukawa_van_vliet.pdf

15:02 Two-Point Functions in the D3-D5 Defect Conformal Field Theory

Boundary conditions and extended operators or defects are fundamental aspects of quantum field theory (QFT). Yet, they are generally poorly understood in higher-dimensional interacting QFTs because explicit computations are often intractable. Progress can be made by imposing highly restrictive symmetries. A particularly prominent example in 4d is the maximally supersymmetric Yang-Mills (SYM) theory. In this talk I will discuss an interface between two copies of N=4 SYM theory whose unitary gauge groups on either side have different rank. Owing to its holographic dual, this system is often called the D3-D5 defect conformal field theory (DCFT) with flux. It preserves some supersymmetry and conformal symmetry, which make it amenable to study using a variety of techniques. In particular, I will describe how perturbation theory and the superconformal bootstrap can be used to obtain new results about the two-point function of protected bulk operators and to constrain the DCFT data. This talk is based on work in progress with Jonah Baerman and Charlotte Kristjansen.

Speaker: Adam Chalabi (Niels Bohr Institute)

D3D5_2-pt_fns_DESY.pdf

14:00 → 15:30 Parallel Session Thursday: Dark Matter Session

Convener: Bibhushan Shakya

14:10 How could we probe the angular dependence of dark matter self-interactions?

Dark Matter

Speaker: Moritz Fischer (LMU Munich)

MoritzFischer.pdf

14:30 X-rays constraints on sub-GeV Dark Matter

We present updated constraints on 'light' Dark Matter (DM) particles with masses between 1 MeV and 5 GeV. In this range, we can expect DM-produced $e^\pm$ pairs to upscatter low-energy ambient photons in the Milky Way via the Inverse Compton process, and produce a flux of X-rays that can be probed by a range of space observatories. Using diffuse X-ray data from XMM-Newton, INTEGRAL, NuSTAR and Suzaku, we compute the strongest constraints to date on annihilating DM for 200 MeV $< m_{\rm DM} <$ 5 GeV and decaying DM for 100 MeV $< m_{\rm DM} <$ 5 GeV.

Based on the recent work 2303.08854 and the previous work 2007.11493.

Speaker: Jordan Koechler (LPTHE - Sorbonne University)

2023_DESY_Talk.pdf

14:50 Excited bound states and their role in dark matter production

We explore the impact of highly excited bound states on the evolution of number densities of new physics particles, specifically dark matter, in the early Universe. Focusing on dipole transitions within perturbative, unbroken gauge theories, we develop an efficient method for including around a million bound state formation and bound-to-bound transition processes. This enables us to examine partial-wave unitarity and accurately describe the freeze-out dynamics down to very low temperatures. In the non-Abelian case, we find that highly excited states can prevent the particles from freezing out, supporting a continuous depletion in the regime consistent with perturbativity and unitarity. We apply our formalism to a simplified dark matter model featuring a colored and electrically charged t-channel mediator. Our focus is on the regime of superWIMP production which is commonly characterized by a mediator freeze-out followed by its late decay into dark matter. In contrast, we find that excited states render mediator depletion efficient all the way until its decay, introducing a dependence of the dark matter density on the mediator lifetime as a novel feature. The impact on the viable dark matter mass can amount to an order of magnitude, relaxing constraints from Lyman-α observations.

Speaker: Tobias Binder (TU München)

TBinder_DESY2023.pdf

15:10 Exploring freeze-out and freeze-in dark matter through the flavon portal

Motivated by the dynamical reasons for the hierarchical structure of the Yukawa sector of the Standard Model (SM), we consider an extension of the SM with a complex scalar field, known as `flavon', based on the Froggatt-Nielsen mechanism. In an effective theory approach, the SM fermion masses and mixing patterns are generated in orders of the parameter related to the vacuum expectation value of the flavon field and the cut-off of the effective theory. By introducing right-handed neutrinos, we study the viability of the lightest right-handed neutrino as a dark matter candidate, where the same flavon field acts as a mediator between the dark and the SM sectors. We find that dark matter genesis is achieved both through freeze-out and freeze-in mechanisms encompassing the $\mathcal{O}(\text{GeV})$ -- $ \mathcal{O}(\text{TeV})$ mass range of the mediator and the dark matter particle. In addition to tree-level spin-dependent cross section, the model gives rise to tree- and loop-level contributions to spin-independent scattering cross section at the direct detection experiments such as XENON and LUX-ZEPLIN which can be probed in their future upgrades. By choosing suitable Froggatt-Nielsen charges for the fermions, we also generate the mass spectrum of the SM neutrinos via the Type-I seesaw mechanism. Flavor-changing neutral current processes, such as radiative lepton decay, meson mixing, and top-quark decay remain the most constraining channels and provide testability for this minimal setup that addresses several major shortcomings of the SM.

Speaker: Tom Tong (Universität Siegen)

Flavon.pdf

14:00 → 15:30 Parallel Session Thursday: Phenomenology I

14:00 Analytic continuation of Greens' functions using neural networks

In quantum many-body physics, the analytic continuation of Greens' functions is a well-known problem.
The problem is ill-posed in the sense that the transformation kernel becomes chaotic for large energies and thus small noise
creates huge differences in the resulting spectral density function.
Some techniques in the field of machine learning, in particular neural networks, are known for handling this kind of problem.
Using a neural network and for the problem-optimized loss functions and hyperparameters, a network is trained to determine
the spectral density from the imaginary part of the Greens function given by quantum Monte Carlo simulations.
The network is able to recover the overall form of the spectral density function, even without adding constraints such as
normalization and positive definiteness.
There is no need to encode these constraints as regularizations since they are reflected automatically by the solution provided by the network.
This indicates the correctness of the inversion kernel learned by the neural network.
In the talk, I will explain the structure of the methods used to train the network and highlight the central results.

Speaker: Yanick Thurn (Julius-Maximilians Universität Würzburg)

analytic_continuation_15min.pdf

14:22 Soft photon emission at the LHC and LBK theorem

The emission of soft photons plays a fundamental role in our understanding of quantum field theories. However, the calculations for one-photon emission observables appear to be incompatible with the experimental measurements. Future upgrades to the ALICE detector at the LHC are proposed to measure soft photon emission, which is of great interest. Predictions for processes involving soft photons, up to next-to-leading power (NLP) in the photon's energy, can be obtained using the Low-Burnett-Kroll (LBK) theorem. In this talk, I propose a form of the LBK theorem which relies on evaluation of the non-radiative amplitude with on-shell, physical momenta. We use this form to numerically study the impact of NLP contributions to cross-sections for $pp$ and $e^-e^+$ processes involving soft photon emission.

Speaker: Roger Balsach (University of Münster, Institute of Theoretical Physics)

DESYTW_Balsach.pdf

14:44 Efficient computation of Hankel transforms based on Levin’s method

In the most commonly adopted approach to transverse momentum-dependent (TMD) factorization, the TMD parton distributions are expressed in position space, which is Fourier-conjugate to the transverse momenta. The transverse momentum-dependent observables are obtained through a two-dimensional Fourier transform, which can be reduced to a one-dimensional Hankel transform. Computation of this quantity is numerically challenging due to the presence of highly oscillatory integrals, which hinder accurate extraction of parton distributions from experiments.

In our work, we have developed an algorithm for the efficient computation of Hankel transforms based on Levin's method [1]. This method combines speed and precision, simultaneously utilizing a fixed grid in the position space in a wide range of transverse momenta. Our approach is integrated into ChiliPDF library [2]. In this talk, I will describe Levin's method, provide an outline of the algorithm, and present a comparison of its precision against that of adaptive methods [3].

[1] D. Levin, Fast integration of rapidly oscillatory functions, J. of Computational and Applied Mathematics 67 (1996) 95-101.
[2] M. Diehl, R. Nagar, F. Tackmann, ChiliPDF: Chebyshev interpolation for parton distributions, Eur.Phys.J.C 82 (2022) 3, 257.
[3] Z.B. Kang, A. Prokudin, N. Sato, J. Terry, Efficient Fourier Transforms for Transverse Momentum Dependent Distributions, Comput. Phys. Commun. 258, 107611 (2021).

Speaker: Oskar Grocholski (T (Theorie))

Presentation_Grocholski.pdf

15:06 Entanglement entropy and proton's structure

I am going to discuss the results of the entanglement entropy of proton's constituents as have been obtained recently within Kharzeev-Levin approach. The proposal resolves the paradox coming from the fact that the proton is a pure state but its constituents are incoherent states of partons. The resulting entropy formula can be shown to describe measured data as well as agrees with thermodynamic entropy obtained by myself in 2011 under the assumption of saturation of gluon density.

Speaker: Krzysztof Kutak (Institute of Nuclear Physics Polish Academy of Sciences)

entanglement.pdf

15:30 → 15:50 Coffee break

15:50 → 17:20 Parallel Session Thursday: Strings / Mathematical Physics IV

Convener: Anne Spiering (Trinity College Dublin)

15:50 Quantum information geometry of driven CFTs

Driven quantum systems exhibit a large variety of interesting and sometimes exotic phenomena. In this talk, I study driven two-dimensional conformal field theories from spacetime and quantum information geometric points of view. First, I show that a large class of driving protocols can be realized by coupling the CFT to a time-dependent background spacetime metric. I will do this in the operator formulation as well as in the path integral description of the CFT and elucidate some puzzles. The spacetime driving gives rise to a universal class of CFT states, dubbed Virasoro states, for which I present a quantum information geometry based on relative entropy. If time permits, I will use the information geometry to characterize CFTs periodically driven by the Mobius group. The talk is based on arXiv:2306.00099.

Speaker: Jani Kastikainen (Wurzburg U.)

DESY_talk_Kastikainen_V5.pdf

16:08 JT gravity on hyperbolic lattices and discrete holography

In recent years the search for a holographic duality, which is based on tessellations of the hyperbolic plane has gained momentum and the construction of suitable boundary theories has been considered in the literature. We propose a discrete analog of JT gravity, defined on hyperbolic lattices as a dual bulk theory. We calculate the partition function in the Schwarzian regime, through an inflation rule, which is used to construct the lattice layer by layer. Furthermore we study the spacetime fluctuations of this system by mapping the bulk theory to an Ising model. The phase transition of this model is studied analytically through a mean field approach, as well as numerically.

Speaker: Jonathan Karl (Julius-Maximilians-university Würzburg)

DESY Talk Discrete JT.pdf

16:26 Complexity of a Quantum Circuit with Primary Fields in the Circuit Generator

In this talk I investigate a quantum circuit in a two-dimensional conformal field theory whose generating Hamiltonian includes primary fields. The motivation in the context of AdS/CFT is to access new bulk geometries dual to simple quantum circuits. The gate set of the boundary circuits, based on the stress tensor in previous work, is expanded through the inclusion of primary fields. I will present a simple model circuit where trivial time evolution is perturbed by a marginal primary for a finite time. The expectation value of the energy, the Fubini-Study cost and the quantum circuit complexity are derived to second order in perturbation theory. At late times, we find linear growth of complexity and an energy expectation value that suggests Vaidya black hole collapse as bulk dual. Based on work with Anna-Lena Weigel and Johanna Erdmenger.

Speaker: Tim Schuhmann (Julius-Maximilians-Universität Würzburg, Lehrstuhl für Theoretische Physik III)

DESY_Schuhmann.pdf

16:44 Soft Scattering and Holography: BMS Symmetries in Higher Dimensions

In four spacetime dimensions, soft theorems concerning the factorization of amplitudes with soft gravitons are related to the BMS asymptotic symmetries of the spacetime. In particular, subleading soft theorems are associated to the BMS transformations usually called superrotations. They identify a scattering mode that behaves at the boundary like the stress tensor of a two-dimensional CFT. This discovery paved the way for the Celestial Holography approach to the Flat Spacetime Holography Problem. Although soft gravitational theorems also hold in higher dimensional theories, their asymptotic symmetry counterpart has long been elusive in dimensions greater than four. This talk depicts the construction presented in 2304.09330 [hep-th] of the simplest class of solutions of Einstein equations in higher even dimensions where BMS symmetries are consistently defined - with a local and covariant renormalization of the symplectic form - and related to soft theorems. In the process, some interesting analogies with AdS/CFT will be noted.

Speaker: Federico Capone (Institute for Theoretical Physics - Friedrich Schiller University - Jena)

FC_DESY23.pdf

17:02 Quantum Chaos and Complexity in Triangular Billiard Systems

In light of recent advancements made towards quantifying quantum chaos in dynamical systems, and motivated by the search for viable definitions of complexity in quantum field theory and holography, we revisit quantum billiards and examine the recently proposd measure of Krylov state complexity known as spread complexity. In particular, we investigate the growth of Krylov state complexity in the system of triangular billiard systems with both rational and irrational angles, which we take to be the boundary of two-dimensional infinite potential boxes. While classically, these billiards exhibit zero Lyapunov exponent, quantum mechanically they display exponential growth of out-of-time-order-correlations (OTOC) and Krylov complexity. We further investigate higher moments of Krylov state complexity as well as new universality classes among them. Normally, the level spacing statistics follow Gaussian orthogonal ensemble statistics, but deviations caused by scarring and supscarring mechanisms occur. We further create a hierarchy of chaotic nature of these triangles by studying their growth of spectral complexity. This work has future directions of using new quantum chaos quantifiers to establish a quantum mechanical ergodic hierarchy, and may point towards new holography duals of complexity.

Speaker: Rathindra Nath Das (Univ. Würzburg)

DESY_RND_QCCTB.pdf

15:50 → 17:20 Parallel Session Thursday: Strings / Mathematicals Physics II

Convener: Craig Lawrie (T (Theorie))

15:50 Higher-Point Conformal Blocks From the Oscillator Formalism

We explore a novel aproach towards the analytical computation of higher-point conformal blocks. The method of interest, which we call oscillator formalism, proves to be very efficient in two dimensions. In particular, the known result for the general $n$-point block in the comb channel can be rederived in a straight-forward manner. But also torus conformal blocks can be obtaind from this method. Moreover, we discuss generalizations for CFTs in higher dimensions.

Speaker: Tobias Hössel

DESY_CFT23_Talk_TobiasHoessel.pdf

16:08 Numerical Six-point Bootstrap

The numerical conformal bootstrap rigorously bounds OPE data of unitary CFTs by excluding solvability of four-point crossing equations through semi-definite programming techniques. Extending to multi-point correlators can provide access to new data that could otherwise only be extracted from infinite four-point systems. Indeed, recent work of D. Poland, V. Prilepina and P. Tadić shows that numerically solving truncated crossing equations for five-point correlators produces approximate OPE data with reasonable heuristic estimates of the errors. However, it remains unclear how the constraints set by unitarity could be exploited in a multi-point setting, leading to rigorous bounds analogous to those of the four-point bootstrap. The purpose of this talk is to make a concrete proposal for achieving this goal through six-point correlators. The proposal is supported by numerical results of a 1d implementation.

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

DESY_Theory_Workshop__Numerical_Six_point_Bootstrap.pdf

16:26 Hecke Operators

In the context of the Analytic Version of the Geometric Langland correspondence, Hecke operators, and their eigenvalue properties, play a very important role.

In this work, we explicitly propose a representation of Hecke modification acting on conformal blocks for the $H_3^+$ WZW model away from the critical level limit. This proposal reduces to the known result in the literature once we restrict it to the critical level.
We use this construction to show explicitly that the Hecke Eigenvalue Property follows in this model as a consequence of the SOV transform between the correlation functions of the $H_3^+$ model and Liouville theory.

Speaker: Federico Ambrosino (T (Stringtheory))

Hecke slides.pdf

16:44 On the Boundary Conformal Field Theory Approach to Symmetry-Resolved Entanglement

We study the symmetry resolution of the entanglement entropy of an interval in two-dimensional conformal field theories (CFTs), by studying the decomposition of the partition function into charge sectors of the respective symmetry in the presence of boundary conditions at the entangling points. Symmetry resolution provides a more refined entanglement measure and can therefore provide more information about the nature of quantum states in QFT. We demonstrate that the decomposition already provides the symmetry resolution of the entanglement spectrum of the corresponding bipartition. Considering the various terms of the partition function associated with the same charge sector the symmetry-resolved Rényi entropies can be derived to all orders in the UV cutoff expansion without the need to compute the charged moments. We apply this idea to the theory of a free massless boson with $U(1)$, $\mathbb{R}$ and $\mathbb{Z}_2$ symmetry. We find equipartition in the $U(1)$ and $\mathbb{R}$ cases to all orders in the cutoff expansion.

Speaker: Henri Scheppach (Julius-Maximilians-Universität Würzburg)

Presentation_TW_DESY.pdf

16:00 → 17:30 Parallel Session Thursday: Dark Matter Session

Convener: Bibhushan Shakya

16:00 Assessing the Role of Finite Temperature Corrections in Dark Matter Freeze-In

Models of feebly-interacting Dark Matter (DM) have gained popularity due to the non-observation of DM in direct detection experiments. Unlike DM freeze-out, which occurs when the dark sector particles are non-relativistic, feebly-interacting DM is primarily produced at temperatures corresponding to the heaviest mass scale involved in the production process. As a result, quantum and finite temperature corrections can significantly alter the predictions for the DM production rate and hence for its relic abundance. However, current calculations often rely on the conventional Boltzmann equation approach performed at either zero temperature or with thermal masses to regulate infrared divergences in scattering amplitudes throughout all temperature regimes. In this talk, I will discuss some recent advancements of an ongoing effort to consistently calculate the DM production rate from first principles, combining the real-time approach of thermal quantum field theory with Schwinger–Dyson equations derived from a two-particle irreducible (2PI) effective action. We compare our results with the Boltzmann approach, both in vacuum and by using thermal masses, and with different approximations for the in-medium propagators. Moreover, we discuss the applicability and accuracy of these various approaches for phenomenological studies.

Speaker: Emanuele Copello

Copello_DESYTHW23_CTP.pdf

16:20 Gravitational Axiverse Spectroscopy: Seeing the forest for the Axions

We consider inflationary models with multiple spectator axions that couple to Abelian
(and non-Abelian) dark gauge sectors. We demonstrate two distinctive phenomena that
make this class of models attractive – first, the gravitational wave peak produced by
axions coupled to dark Abelian sectors can coherently sum, leading to an enhanced
signal. Second, we show that separation of the gravitational wave peaks can occur,
depending on the axion initial conditions and mass. This leads to a distinctive
gravitational wave forest, whose observation would be a signal that multiple axions exist
within the universe. We relate these models to the recent PTA observations. Finally, we
discuss the UV embedding of these models in the context of string theory and the Axiverse.

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

Gravitational_Axiverse_Spectroscopy_DESYt.pdf

16:40 Dark Matter Phenomenology in Z’2 broken Two Higgs Doublet Model with Complex Singlet Extension

Although the Standard Model is very successful, there are still open
problems which it cannot explain, one of it being dark matter (DM).
This has led to various Beyond Standard Model theories, of which Two
Higgs Doublet models are very popular, as they are one of the simplest
extensions and lead to a rich phenomenology. Further extensions with
a complex singlet lead to a natural DM candidate.
The aim of this work is to explore the dark sector in a Two
Higgs Doublet Model extended by a complex scalar singlet, where the
imaginary component of the singlet gives rise to a pseudo-scalar DM
candidate. Both, the doublets, and the singlet, obtain a vacuum ex-
pectation value (vev), where the singlet vev leads to additional mixing
of the doublet and the singlet scalar sector. We examine the influence
of the Higgs sector parameters on DM relic density as well as direct and indirect detection cross sections. The results are then compared with
constraints from experiments.

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

2HDMS_presentation_version_5.pdf

17:00 Informal discussion session

16:00 → 17:30 Parallel Session Thursday: Phenomenology II

16:00 The electroweak rho parameter and the W boson mass in the NMSSM at two-loops

We present the prediction of the electroweak $\rho$ parameter and the $W$ boson mass in the CP-violating Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM) at the two-loop order. The $\rho$ parameter is calculated at the full one-loop and leading and sub-leading two-loop order $\mathcal{O}(\alpha + \alpha_t\alpha_s + \left(\alpha_t+\alpha_\lambda+\alpha_\kappa\right)^2)$. The new $\Delta \rho$ prediction is incorporated into a prediction of $M_W$ via a full supersymmetric (SUSY) one-loop calculation of $\Delta r$. We show some first phenomenological applications with the emphasis on the importance of a proper combination with the known SM higher-order corrections.

Speaker: Martin Gabelmann (T (Phenomenology))

mgabelmann_wmass.pdf

16:22 N3LO Drell-Yan cross-sections confront data at several center-of-mass energies

With the recent computation of cross-section calculations up to the third order in perturbative QCD, and the appearance of the first PDF fits at N3LO (albeit only approximately), it becomes interesting to study if the improved precision is accompanied by an analogue improvement in accuracy in describing experimental data.

To this aim, we calculated the theoretical total cross-sections for charged and neutral-current Drell-Yan production at NNLO and N3LO in QCD and NLO in EW couplings using different NNLO and the aN3LO PDF sets.
We then performed a systematic comparison of these predictions with measurements performed at $\mathrm{p}\mathrm{p}$ and $\mathrm{p}\overline{\mathrm{p}}$ colliders at different center-of-mass energies.

Speaker: Federico Vazzoler (CMS (CMS Fachgruppe QCD))

N3LOXS_Vazzoler_final.pdf

16:44 Theoretical concepts and measurement prospects for BSM trilinear couplings: a case study for scalar top quarks

Following the potential discovery of new heavy particles at the LHC or a future collider, it will be crucial to determine their properties and the nature of the underlying Physics. In this context, the possibility of Beyond-the-Standard-Model (BSM) scalar trilinear couplings is of particular interest.
In this talk, I will consider as a specific example the scalar top (stop) trilinear coupling parameter, which controls the stop–stop–Higgs interaction, and I will discuss possible strategies for its experimental determination. I will show that the best prospects for determining the stop trilinear coupling arise from quantum effects entering the prediction for the mass of the SM-like Higgs boson compared to its measured value. Furthermore, the Higgs mass exhibits a high sensitivity to the stop trilinear coupling even for heavy masses of the BSM particles.
Next, I will review different renormalisation prescriptions for the stop trilinear coupling, and their impact in the context of Higgs mass calculations. I will show that a mixed renormalisation scheme is preferred in view of the present level of accuracy of this calculation, and I will clarify the source of potentially large logarithms that cannot be resummed using standard renormalisation group methods.

Speaker: Johannes Braathen (DESY)

Braathen_DESY-TH23.pdf

17:30 → 18:45 Hertz Lecture - Robert Myers

Why We Explore

19:00 → 21:00 Conference dinner

Friday 29 September

09:00 → 13:00 Plenary Sessions Friday

Convener: Martin Ammon & Elli Pomoni

09:00 The statistical interpretation of semi-classical gravity

Speaker: J. de Boer (Amsterdam)

09:40 A tensor model for chaotic CFT

Speaker: J. Sonner (U. Geneva)

DESYTalkSonner.pdf

10:20 Generalized Black Hole Entropy as von Neumann Entropy

It was recently shown that the von Neumann algebras of observables gravitationally dressed to the mass of a Schwarzschild-AdS black hole or an observer in de Sitter spacetime are Type II, and thus admit well-defined traces. The von Neumann entropies of "semi-classical" states was then found to be equal to the generalized entropy. We present a general framework for obtaining the algebra of dressed observables for linear fields on any spacetime with a Killing horizon. We prove, assuming the existence of a stationary (but not necessarily KMS) state and suitable asymptotic decay of solutions, that the algebra of dressed observables exterior to the Killing horizon always contains a Type II factor of observables "localized" on the horizon. Applying our general framework to the algebra of observables in the exterior of an asymptotically flat Kerr black hole, where the fields are dressed to the black hole mass and angular momentum, we find that the algebra is the product of a Type II∞ algebra on the horizon and a Type I∞ algebra at past null infinity. In Schwarzschild-de Sitter, despite the fact that the spacetime is spatially closed, the quantum field observables are dressed to the perturbed areas of the black hole and cosmological horizons yielding a product of Type II∞ algebras on each horizon. Our results suggest that in all cases where there exists additional "boundary structure" (e.g., an asymptotic boundary or another Killing horizon) the algebra of observables is Type II∞ and in the absence of such structures (e.g., de Sitter) the algebra is Type II1.

Speaker: S. Leutheusser (Princeton)

PDF slides Generalized Entropy - DESY.pdf

11:00 Coffee break

11:30 New perspectives on QFT transport

Speaker: M. Heller (Ghent University)

12:10 Complexity Equals (Almost) Anything

Speaker: R. Myers (Perimeter Inst.)

Myers DESY23.pdf

13:00 → 13:05 Closing