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DESY Virtual Theory Forum 2020

22–25 Sept 2020
DESY Hamburg
Europe/Berlin timezone

Contribution List

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96. REVIEW TALK: Recent ideas for dark matter detection
Yonit Hochberg
22/09/2020, 13:45
8. Precise dark matter relic abundance in decoupled sectors
Mr Paul Frederik Depta (DESY)
22/09/2020, 14:15
Dark matter (DM) as a thermal relic of the primordial plasma is increasingly pressured by direct and indirect searches, while the same production mechanism in a decoupled sector is much less constrained. We extend the standard treatment of the freeze-out process to such scenarios and perform precision calculations of the annihilation cross section required to match the observed DM abundance....
33. Axion Gegenschein: Dark Countersources of Bright Radio Objects
Oindrila Ghosh (II. Institute for Theoretical Physics, University of Hamburg)
22/09/2020, 14:28
I will describe a new scheme for the detection of radio signals from the decay of axions and axion-like particles, called *axion gegenschein*, using next-generation facilities such as SKA. Ambient radiation arriving from astrophysical radio-bright objects drive stimulated decay in the Galactic halo creating a *countersource* with the dimensions and morphological features of each source in the...
63. Axion emissivity from photon conversions in the solar magnetic field
Mrs Ersilia Guarini (Physics Department, University of Bari)
22/09/2020, 14:41
Axions can be produced in the Sun via the Primakoff process leading to conversions of thermal photons into axions in the flucutuating electric and magnetic fields generated by the charged particles in the stellar plasmas. Currently this flux is searched by the helioscope experiment CAST at CERN. A future generation helioscope experiment, called IAXO, is currently under investigation. Seismic...
72. Landscape instabilities from finite density effects
Mr Stefan Stelzl (TUM Munich)
22/09/2020, 14:54
We consider finite density effects in models with a metastable ground state. We find that sufficiently dense objects, such as neutron stars, can destabilise the metastable minimum allowing for classical formation of bubbles of a new vacuum. As we show, these bubbles are not necessarily confined to the dense region, but can escape to infinity. This leads to a phase transition in the universe...
20. Enlarging the ALP Dark Matter window with axion fragmentation
Dr Cem Eröncel (DESY)
22/09/2020, 15:07
Axion-like-particle (ALP) is a well-motivated candidate for dark matter, and it is subject to extensive theoretical and experimental research in recent years. The ALP production mechanisms mostly studied in the literature are misalignment, thermal production in the plasma, and decay of cosmic strings. Recently, a new mechanism, axion fragmentation, has been proposed. It can arise if the axion...
52. Audible Axions
Mr Wolfram Ratzinger (Johannes Gutenberg University Mainz)
22/09/2020, 15:20
Conventional approaches to probing axions and axion-like particles (ALPs) typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. We show that such invisible axions, which are viable candidates for dark matter, can produce a stochastic gravitational wave background in the...
11. Resonant backreaction in axion inflation
Yvette Welling (DESY)
22/09/2020, 15:33
Axion inflation entails a coupling of the inflaton field to gauge fields through the Chern-Simons term. This results in a strong gauge field production during inflation, which backreacts on the inflaton equation of motion. We show that this strongly non-linear system generically experiences a resonant enhancement of the gauge field production, resulting in oscillatory features in the inflaton...
97. REVIEW TALK: New ideas from the neutrino sector
Mariam Tortola
22/09/2020, 16:15
78. Relaxing Cosmological Neutrino Mass Bounds with Unstable Neutrinos
Miguel Escudero (TUM)
22/09/2020, 16:45
At present, cosmological observations set the most stringent bound on the neutrino mass scale. Within the standard cosmological model (ΛCDM), the Planck collaboration reports $\Sigma m_\nu < 0.12$ eV at 95% CL. This bound, taken at face value, excludes many neutrino mass models. However, unstable neutrinos, with lifetimes shorter than the age of the universe $\tau_\nu < t_U$, represent a...
27. Shining Light on the Scotogenic Model: Interplay of Colliders and Cosmology
Mr Sven Baumholzer (Johannes Gutenberg-Universitaet Mainz)
22/09/2020, 16:58
In the framework of the scotogenic model, which features radiative generation of neutrino masses, we explore light dark matter scenario. Throughout the paper we chiefly focus on keV-scale dark matter which can be produced either via freeze-in through the decays of the new scalars, or from the decays of next-to-lightest fermionic particle in the spectrum, which is produced through...
6. Massive neutrinos in non-linear LSS
Mr Petter Taule (Technical University of Munich)
22/09/2020, 17:11
Current and near future surveys are expected to map out the large-scale structure of the Universe at unprecedented precision. In order to extract information from observational data, a solid theoretical understanding is required, and in recent years considerable efforts has been dedicated to model the weakly non-linear regime using perturbative methods. In this talk, I will describe an...
46. Probing baryogengesis using synergy between $n-\bar{n}$ oscillation and collider searches
Dr Chandan Hati (Technische Universität München, James-Franck-Straße 1, D-85748 Garching, Germany)
22/09/2020, 17:24
Neutron-antineutron ($n-\bar{n}$) oscillation violates baryon number by two units and an observable rate of such a process would strongly advocate physics beyond the Standard Model (BSM). Many prospective future experiments such as ESS and DUNE are planning to search for $n-\bar{n}$ oscillation improving on the current limits. In this talk, we will discuss the impact of the observation of...
15. Influence of a magnetic field on beta-processes in supernova matter
Dr Alexandra Dobrynina (P. G. Demidov Yaroslavl State University &amp; University of Hamburg)
22/09/2020, 17:37
An influence of a magnetic field on beta-processes is investigated under conditions of a core-collapse supernova. For realistic magnetic fields reachable in astrophysical objects we obtain simple analytical expressions for reaction rates of beta-processes as well as the energy and momentum transferred from neutrinos and antineutrinos to the matter. Based on the results of one-dimensional...
58. Bounds on axion-like particles from the diffuse supernova flux
Mr Pierluca Carenza (Università degli Studi di Bari)
22/09/2020, 17:50
The cumulative emission of Axion-Like Particles (ALPs) from all past core-collapse supernovae (SNe) would lead to a diffuse flux with energies ${\mathcal O}(50)$ MeV. We use this to constrain ALPs featuring couplings to photons and to nucleons. ALPs coupled only to photons are produced in the SN core via the Primakoff process,and then converted into gamma rays in the Galactic magnetic field....
10. A hybrid simulation of gravitational wave production
Mr Henrique Rubira (DESY)
22/09/2020, 18:03
LISA telescope will be specially interesting to probe the scenario of a first order phase transition happening close to the electroweak scale. Recently, it became evident that the main contribution to the GW spectra would come from the sound waves propagating through the plasma. Current estimates of the GW spectra are based on numerical simulations of a scalar field interacting with the plasma...
92. REVIEW TALK: Standard Model
Lorenzo Tancredi (CERN TH)
23/09/2020, 13:45
60. Unveiling the Higgs at FCC-hh with new diboson precision measurements.
Mr Alejo Nahuel Rossia (DESY, HU Berlin)
23/09/2020, 14:15
The lack of evidence of New Physics coming from direct searches of resonances at the LHC calls for an increase in efforts to devise new observables that can indirectly probe New Physics. Additionally, the future FCC-hh will make available new processes, inaccessible so far due to their low number of events. Studying the high transverse momentum distribution of diboson production processes at...
68. Constraining the Top EFT
Mr Sebastian Bruggisser (ITP Heidelberg)
23/09/2020, 14:30
I will discuss a global analysis of Run II top measurements at the LHC in terms of dimension-6 operators. A distinctive feature of the top sector is the large number of four-fermion operators. This potentially leads to a large number of degeneracies. I will show in detail how those degeneracies can be resolved and how quadratic terms lead to stable limits on each of the Wilson coefficients.
76. On the Phenomenology of the GRSMEFT
Mr Maximilian Dichtl (TUM)
23/09/2020, 14:45
We present collider probes of the GRSMEFT, the most general effective field theory of gravity coupled to the SM of particle physics. In particular, we focus on graviton production in association with a jet, for which we derive the leading new-physics scattering amplitude, the expected cross section, and compare with missing energy searches at the LHC in order to bound the size of the relevant...
69. $\Delta F=1$ effective Hamiltonian in generic extensions of the Standard Model
Ulserik Moldanazarova (University of Liverpool)
23/09/2020, 15:00
In this talk we will discus the flavour violating four-fermion interactions and dipole interaction in models with extra heavy particles whose masses are equal to or above the electro-weak scale. We use the Becchi-Rouet-Stora-Tyutin symmetry to constrain tree-level couplings to construct perturbatively unitary theories, for which we calculate one-loop corrections. We focus on the gauge...
38. Renormalization and scale evolution of the soft-quark soft function
Ms Bianka Mecaj (Johannes Gutenberg University)
23/09/2020, 15:15
Soft functions enter in factorization theorems in soft collinear effective field theory (SCET) and they capture the large distance effects of a process. They are defined as matrix elements of soft fields dressed by Wilson lines. While at leading order in power counting they are described by emissions of soft gauge bosons at sub-leading order one needs to consider emissions of soft fermions...
77. FlexibleDecay: An automated calculator of scalar decay widths
Dr Wojciech Kotlarski (TU - Dresden)
23/09/2020, 15:30
We present FlexibleDecay - a tool to calculate decays of scalars in arbitrary BSM models. BSM effects are taken into account at the leading order - meaning that for loop induced decays all one-loop BSM contributions are automatically included. In case of scalar and pseudoscalar Higgs boson decays the known higher order SM QED, QCD and EW effects are taken into account where possible....
93. REVIEW TALK: High-intensity probes of dark sector particles
Stefania Gori (UCSC)
23/09/2020, 16:15
48. Probing lepton number violating interactions in rare kaon decays
Kåre Fridell (Technical University of Munich)
23/09/2020, 16:45
We investigate the possibility to probe lepton number violating (LNV) operators in the rare kaon decay $K\to\pi\nu\nu$. Performing the analysis in the Standard Model effective field theory with only light active Majorana neutrinos, we determine the current limits on the corresponding LNV physics scale from the past E949 experiment at BNL as well as the currently operating experiments NA62 at...
62. New ways to probe CP-violation and lepton non-universality with rare charm decays
Mr Rigo Bause (TU Dortmund)
23/09/2020, 17:00
Rare $|\Delta c|=|\Delta u|=1$ processes are unique probes of flavour physics in the Standard Model (SM) and beyond and provide an excellent opportunity to analyse CP-violation and search for new physics (NP) due to their strong GIM-suppression in the SM. Furthermore, a variety of null test observables is available for decays, such as $D\to \pi \ell^+ \ell^-$, $\ell = e,\,\mu$, and provide...
25. Axionlike Particles and Lepton-Flavor Violation
Mr Marvin Schnubel (Johannes Gutenberg-University Mainz)
23/09/2020, 17:15
Axionlike Particles (ALPs) appear in many well-motivated extensions of the Standard Model. Their lepton-flavor violating couplings can be probed in exotic muon and tau decays. When ALPs are produced resonantly, the sensitivity of three-body decays such as $\mu\to3e$ and $\tau\to3\mu$ exceeds that of radiative decays like $\mu\to e\gamma$ and $\tau\to\mu\gamma$ by multiple orders of magnitude....
3. QCD axion EFT under the loop
Gonzalo Alonso Álvarez (Heidelberg University)
23/09/2020, 17:30
The low-energy phenomenology of the QCD axion is usually studied in a model-independent way using an effective Lagrangian. However, one-loop processes that exhibit logarithmic divergencies are sensitive to the high-energy completion of each specific model. This is extremely important for some axion searches, like the ones conducted at Kaon facilities such as NA62 that aim to look for the rare...
66. EFTs of axions and gauge bosons in the light of UV models
Quentin Bonnefoy (DESY)
23/09/2020, 17:45
I will revisit EFT couplings between an axion and massive gauge bosons. It is known that massive vectors allow for more freedom than massless ones when building an EFT, thanks to the existence of the non-linear realization of (gauge) symmetries. It is also known that such a non-linear realization must sometimes be used even to describe physics at energy scales above the electroweak vev, due to...
61. Asymptotic Safety with Higgs and Flavor Portals
Ms Clara Hormigos-Feliu (TU Dortmund)
23/09/2020, 18:00
Standard Model extensions inspired by asymptotic safety generally contain vector-like fermions and singlet matrix scalar fields. Here we study several models where three generations of colorless vector-like fermions allow for portal Yukawa interactions with leptons, leading to rich phenomenological implications. A novel feature is that the enlarged scalar sector, which also contains a Higgs...
89. REVIEW TALK - Geometries for scattering amplitudes, and beyond
Livia Ferro (LMU)
24/09/2020, 13:00
In recent years it has become clear that geometrical structures underlie various observables in quantum field theories. In this talk I will describe amplituhedra, i.e. geometries encoding scattering amplitudes. These pertain to a broader family of geometries called positive geometries, whose basics I will review. The amplitudes are extracted from the canonical form with logarithmic...
34. One integral to rule them all: an algorithm to compute Feynman integrals
Mr Christoph Dlapa (Max Planck Institute for Physics)
24/09/2020, 13:45
Differential equations are a powerful tool for computing Feynman integrals. Their solution is straightforward if one can find a transformation to a certain ‘canonical’ form, where the answer is manifestly given in terms of iterated integrals, such as multiple polylogarithms. An algorithmic way to construct the necessary transformation is therefore highly desired, and recent years have seen...
7. How tropical are seven-, eight- and nine-particle scattering amplitudes?
Niklas Henke (DESY)
24/09/2020, 14:05
Using the symbol bootstrap, loop amplitudes of planar $\mathcal{N}=4$ SYM theory can be obtained from their alphabet, the list of their singularities. The elements of this alphabet, the letters, coincide with the variables of certain cluster algebras. However, at eight and more particles these cluster algebras become infinite, whereas it is believed that the amplitudes only have finitely many...
57. Analytic Structure of all Loop Banana Amplitudes
Mr Christoph Nega (Bethe Center for Theoretical Physics)
24/09/2020, 14:25
Using the Gelfand-Kapranov-Zelevinsk\u{\i} system for the primitive cohomology of an infinite series of complete intersection Calabi-Yau manifolds, whose dimension is the loop order minus one, we completely clarify the analytic structure of all banana amplitudes with arbitrary masses. In particular, we find that the leading logarithmic structure in the high energy regime, which ...
71. Plabic Graphs and Symbol Alphabets in $\mathcal{N}=4$ super-Yang-Mills Theory
Mr Anders Schreiber (Brown University)
24/09/2020, 14:45
A key challenge in the study of scattering amplitudes of $\mathcal{N}=4$ super-Yang-Mills theory is to understand their analytic structure. Symbols, a central tool in this topic, are known to contain particular cluster coordinates of $Gr(4,n)$ together with certain algebraic functions of cluster coordinates. In my talk, I will present an algorithm for computing symbol alphabets by solving...
21. Integrability of Massive Feynman Diagrams
Mr Julian Miczajka (Humboldt-Universität zu Berlin)
24/09/2020, 15:30
Much of the calculational progress in $\mathcal{N}=4$ Super-Yang-Mills theory has been due to its integrability in the planar limit, which presents itself in form of an infinite-dimensional symmetry of Yangian-type. Recently it has been found that certain classes of ubiquituous massive Feynman diagrams feature a similar dual-conformal Yangian symmetry. I report on this progress and show how...
54. Center 1-from symmetries in higher dimensions
Dr Markus Dierigl (UPenn)
24/09/2020, 15:50
In this talk I will summarize recent results on the fate of center 1-form symmetries in six and eight dimensions. In particular, I will discuss their interplay between other gauged higher-form symmetries causing obstructions to the gauging of the discrete center 1-form symmetries, which would result in non-simply connected non-Abelian gauge groups. In this way we can find previously unknown...
70. Emergent Strings in 4D N=1: Uniqueness and Obstructions
Dr Daniel Kläwer (Mainz University)
24/09/2020, 16:10
We revisit infinite distance limits in the Kähler moduli space of F-theory compactifications to 4D with $\mathcal{N}=1$ supersymmetry. At the classical level, it is known that the existence of certain such limits imposes the structure of a rational or genus-one fibration on the three-dimensional base. As the fiber volume vanishes in the limit, wrapping the D3 brane on it gives rise to an...
16. Harmonic Hybrid Inflation
Mrs Nicole Righi (DESY)
24/09/2020, 16:30
I will present a mechanism for realising hybrid inflation using two axion fields with a purely non-perturbatively generated scalar potential. I will show that such model generates observationally viable slow-roll inflation for a wide range of initial conditions while accommodating certain Swampland conjectures. I will focus mainly on two possible avenues to embed harmonic hybrid inflation in...
79. F-theory on mirror dual Calabi-Yaus
Dr Paul-Konstantin Oehlmann (Uppsala University)
24/09/2020, 16:50
In this work we consider pairs of elliptic Calabi-Yau threefolds, related by mirror symmetry that factorizes between fiber and base. Extending work of Berglund and Mayr, this allows us to deduce the mirror dual base and fibration structures which we use to build up a dictionary between two different F-theory SUGRA theories: The mirror acts as a quotient on the base while local gauge group...
49. Islands in the Randall-Sundrum model
Dr Ignacio A. Reyes (Max Planck Institute, Potsdam)
24/09/2020, 17:10
Recent progress in our understanding of the black hole information paradox has lead to a new prescription for calculating entanglement entropies, which involves special subsystems in regions where gravity is dynamical, called *quantum extremal islands*. We present a simple holographic framework where the emergence of these islands can be understood in terms of the standard Ryu-Takayanagi...
4. Mistakes on the way to a good idea: Peccei-Quinn Symmetry. A tribute to Roberto Peccei
24/09/2020, 18:00
I will talk about the development of the idea now known as Peccei Quinn symmetry, and its consequences. I will use this work that I did together with Roberto Peccei to illustrate key features of how science progresses. While the problem we were addressing, and the answer we found for it are quite technical, this will not be a highly technical lecture. Rather it will be a story about our...
95. REVIEW TALK: Gravitational waves from early universe cosmology
Daniel Figueroa
25/09/2020, 13:30
23. Beyond the Standard Models with Cosmic Strings
Mr Peera Simakachorn (UHH and DESY)
25/09/2020, 14:00
A stochastic gravitational-wave (GW) background from cosmic strings spans a broad range of frequencies. By measuring the slope of its spectrum with future GW observatories, we can infer the equation of state of the universe much earlier than the onset of Big-Bang Nucleosynthesis (BBN). In this work, we consider a variety of cosmological scenarios beyond the standard hot-Big-Bang cosmology and...
5. Model-independent energy budget of cosmological first-order phase transitions
Mr Felix Giese (DESY/Hamburg U.)
25/09/2020, 14:12
We study the energy budget of a first-order cosmological phase transition, which is an important factor in the prediction of the resulting gravitational wave spectrum. Formerly, this analysis was based mostly on simplified models as for example the bag equation of state. Here, we present a model-independent approach that is exact up to the temperature dependence of the speed of sound in the...
64. Gradient effects on false vacuum decay in gauge theory
Mr Juan S. Cruz (Technical University Munich)
25/09/2020, 14:24
We study false vacuum decay for a gauged complex scalar field in a polynomial potential with nearly degenerate minima. Radiative corrections to the profile of the nucleated bubble as well as the full decay rate are computed in the planar thin-wall approximation using the effective action. This allows to account for the inhomogeneity of the bounce background and the radiative corrections in a...
47. Far-from-equilibrium dynamics of axion-like particles with broken shift symmetry
Dr Aleksandr Chatrchyan (Heidelberg University, Institute for theoretical physics)
25/09/2020, 14:36
Axion-like particles (ALPs) play an important role in cosmology and, among others, are well motivated dark matter candidates. In the presence of a monodromy the discrete shift symmetry of ALPs can be broken, and this talk is devoted to the rich nonlinear dynamics that becomes available in such systems. We consider coherent oscillations of the field, which trigger the resonant amplification of...
12. Thick Branes in Extra Dimensions and Suppressed Couplings
Ricardo Landim (Techinical University of Munich)
25/09/2020, 14:48
Extra dimensions (ED) have been used as attempts to explain several phenomena in particle physics, such as the hierarchy and flavor problems. The interaction between new mediators in the bulk (vector, scalar of fermion fields) and the Standard Model (SM) particles can be naturally suppressed if one employs a single, flat ED. In this setup, the SM fields are localized in a finite width ‘fat’...
94. REVIEW TALK: Dark matter
Stefan Vogl
25/09/2020, 15:15
18. Direct detection of dark matter: Precision predictions in a simplified model framework
Dr Christoph Borschensky (Eberhard Karls Universität Tübingen)
25/09/2020, 15:45
In my talk, I will present a calculation of the next-to-leading order QCD corrections for the scattering of Dark Matter particles off nucleons in the framework of simplified models with $s$- and $t$-channel mediators. These results are matched to the Wilson coefficients and operators of an effective field theory that is generally used for the presentation of experimental results on...
80. Impact of the bounds on the direct search of bino-like Dark Matter on naturalness
Ms Ghazal Ghafari (Bonn University)
25/09/2020, 16:00
We postulate the WIMP neutralino Dark Matter's interaction with ordinary matter as scattering from the direct detection experiments' nucleon target. Recently, one of the most sensitive direct detection experiments XENON1T submitted an upper bound on the WIMP-Nucleon Spin-Independent elastic cross-section $ \sigma_{SI} $ at $ 4.1 \times 10^{-47} GeV^2 $ for a mass of $ 30 \frac{GeV}{c^2} $. We...
74. How to suppress exponential growth -- on the parametric resonance of photons in an axion background
Dr Elisa Todarello (KIT)
25/09/2020, 16:15
Axion--photon interactions can lead to an enhancement of the electromagnetic field by parametric resonance in the presence of a cold axion background, for modes with a frequency close to half the axion mass. In this paper, we study the role of the axion momentum dispersion as well as the effects of a background gravitational potential, which can detune the resonance due to gravitational...
75. UV Sensitivity of the Axion Mass from Instantons in Partially Broken Gauge Groups
Mr Maximilian Ruhdorfer (Technical University of Munich)
25/09/2020, 16:30
We examine the contribution of small instantons to the axion mass in various UV completions of QCD. We show that the reason behind the potential dominance of such contributions is the non-trivial embedding of QCD into the UV theory. The effects from instantons in the partially broken gauge group appear as “fractional instanton” corrections in the effective theory. These will exhibit unusual...
59. Recursive construction of the operator product expansion in curved space
Dr Markus B. Fröb (Universität Leipzig)
25/09/2020, 17:00
I present a formula for the coupling-constant derivative of the coefficients of the operator product expansion (Wilson OPE coefficients) in an arbitrary curved space, as the natural extension of the quantum action principle. Expanding the coefficients themselves in powers of the coupling constants, this formula allows to compute them recursively to arbitrary order. As input, only the OPE...
24. Asymptotic dynamics on the worldline for spinning particles
Domenico Bonocore (University of Münster)
25/09/2020, 17:20
The worldline representation of the relativistic spinning particles has been known for a long time. Much of the studies focused on the calculation of effective actions, with less attention to open propagators. In 0811.2067 the formalism has been applied to asymptotic states dressed by soft radiation at next-to-leading power (NLP) in the soft expansion. This led to the definition of the...
85. Curvature in Discrete Quantum Gravity
Mr Joren Brunekreef (Radboud University)
25/09/2020, 17:40
Causal Dynamical Triangulation (CDT) is a non-perturbative theory of quantum gravity. It is based on a lattice discretization of general relativity, where the background metric should emerge dynamically. This makes it difficult to construct suitable observables in the model. A recent addition to the list of available CDT observables is the Quantum Ricci Curvature (QRC), which allows one to...
82. Unitary States at the Late Time Boundary of de Sitter
Gizem Sengor (CEICO at the Institute of Physics of the Czech Academy of Sciences)
25/09/2020, 18:00
In this talk we will focus on free scalar fields of various mass on D-dimensional de sitter, define late time boundary states from their late time behavior, discuss how they are classified in terms of irreducible representations of the symmetry group of de Sitter SO(1,D) by considering their inner products and say a few words about their correlators.
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