Synergies Towards the Future Standard Model

23 Sept 2025, 12:00 → 26 Sept 2025, 13:00 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.

 

 

2025-TheoryWorkshop-WEB.pdf

List_of_participants.pdf

Poster Hertz Lecture_2025-WEB.pdf

Tuesday 23 September

12:45 → 13:45 Registration

13:45 → 14:00 Welcome

14:00 → 16:00 Plenary Session Tuesday I

14:00 SMEFT as a probe of new physics at colliders

Speaker: Eleni Vryonidou

DESY.pdf

14:40 Searches for New Physics at the LHC

Speaker: Tamara Vazquez Schröder

72906d5d-f182-42a0-8a81-23b8706c1dce.pdf

15:20 The Flavor Path to New Physics: Status and Future Prospects

Speaker: Claudia Cornella

Cornella_desy.pdf

16:00 → 16:30 Coffee break

16:30 → 18:30 Plenary Session Tuesday II

16:30 The Frontier of QCD Factorization

Speaker: Aditya Pathak

AP_desy_th_workshop_2025.pdf

17:10 Shower Monte Carlo Event Generators

Speaker: Silvia Ferrario Ravasio

2025_09_23_DESY_TH_Ferrario.pdf

17:50 LHC Measurements and HL-LHC Prospects

Speaker: Steven Lowette

0e648374-90a6-4b9c-944d-22a480036faf.pdf

18:30 → 20:00 Reception

Wednesday 24 September

09:00 → 11:00 Plenary Session Wednesday I

09:00 The Higgs Sector, Effectively

Speaker: Ramona Gröber

DESY-groeber.pdf

09:40 Searches for New Physics at the LHC -- Selected theory topics

Speaker: Johannes Braathen

Braathen_DESYTHWorkshop2025.pdf

10:20 Electroweak Cosmological Naturalness

Speaker: Raffaele-Tito d'Agnolo

dagnolo_DESY.pdf

11:00 → 11:30 Coffee break and Group photo

11:30 → 12:50 Plenary Session Wednesday II

11:30 Electroweak processes at high energies

Speaker: Tao Han

2025-DESY0.pdf

2025-DESY0.pptx

12:10 ML for particle physics in the precision era

Speaker: Henning Bahl (University of Chicago)

2025_09_24_DESY_theory_workshop.pdf

12:50 → 14:00 Lunch

14:00 → 17:30 Parallel Sessions Wednesday Cosmo

14:00 Seeded phase transitions

Cosmological phase transitions (PTs) are fascinating events taking place in the first instants of our Universe. First order PTs proceeding via the nucleation and expansion of bubbles are of particular interest as they can impart a strong departure from thermal equilibrium, with important implications for the matter-antimatter asymmetry as well as the copious production of primordial gravitational waves. These phenomenological properties strongly depend on the dynamics controlling bubble nucleation. In a homogenous Universe, critical bubbles formed out of thermal or quantum fluctuations are expected to be spherical in shape, with a nucleation probability that is the same everywhere. This picture, however, can dramatically change if at the time of the PT the Universe contains impurities, or seeds, that can exponentially enhance the nucleation rate in their vicinity. In this talk, I will discuss the general idea behind seeded phase transitions, and provide few natural examples where topological defects, such as strings and domain walls, can play the role of impurities in the early Universe.

Speaker: Simone Blasi (T (Cosmology))

DESYW.pdf

14:18 Electroweak phase transition seeded by DFSZ axion string

We study the possibility that axion strings in the DFSZ model can act as seeds for the electroweak(EW) first-order phase transition. Unlike the KSVZ case, the DFSZ axion strings can couple to the Higgs sector via a "axion-dependent" portal interaction. We analyze the resulting effective theory and find that string-induced EW bubbles have a different feature from usual bubbles or string-seeded bubbles in KSVZ model. In particular, the profile of the bubble is neither spherically symmetric nor axially symmetric. We study the expansion of this bubble and discuss its cosmological implication.

Speaker: Dr Yu Hamada (T (Cosmo))

DESY_TH25_hamada.pdf

14:36 Inverse Bubble from broken Supersimmetry

A cosmological inverse first-order phase transition is an endothermic event in which bubbles of the new phase expand by absorbing latent heat and pulling the surrounding plasma inward—opposite to the usual (exothermic) outward flow. Such behaviour was thought possible only during a reheating phase, when the cosmic temperature rises. We show it can emerge naturally while the Universe cools. In an O’Raifeartaigh model that breaks supersymmetry and $R$-symmetry, the transition along the pseudomodulus is inverse in a part of the parameter space. By solving the hydrodynamics, without approximations, we identify the general criterion to distinguish the PT nature—the sign of the generalized pseudo-trace of the energy–momentum tensor—which cleanly separates inverse from direct transitions. This establishes endothermic phase transitions as a realistic ingredient of early-Universe dynamics and furnishes a concrete SUSY example for broader model building. Work is now underway to compute the associated stochastic-gravitational-wave spectrum, with the goal of distinguishing inverse from direct transitions in upcoming observations.

Speaker: GIULIO BARNI (IFT Madrid)

Inverse_PTs_DESY_Giulio_Barni.pdf

14:54 Gravitational Waves from Inverse Phase Transitions

Inverse phase transitions in which tunneling proceeds into a finite-temperature vacuum away from the zero-temperature vacuum exhibit different fluid profiles than usual (direct) transitions. We investigate the effect this has on the sound wave contribution to the stochastic gravitational wave background generated in such transitions.

Speaker: Eric Madge Pimentel (IFT-UAM/CSIC)

Madge-DESY2025.pdf

15:12 Bubble wall friction in first order phase transitions with symmetry restoration

We study friction effects on the expanding bubble wall in first order phase transitions (FOPT) with symmetry restoration, where particles become massless inside the bubble. We consider leading order (LO) and next-to leading order (NLO) friction effects of the surrounding plasma.

The inverse case, with symmetry breaking, is well studied and shows that LO friction effects decrease the bubble wall expansion but are not sufficient to stop runaway behavior. NLO effects however lead to velocity dependent friction terms which terminate the runaway of the bubble wall.

For the case of symmetry restoring FOPT we find an acceleration of the bubble wall at LO. At NLO we find again an acceleration of the bubble wall for low wall boost factors but also velocity dependent friction terms which decelerate the expansion and terminate the runaway at high wall boost factors. We compare both scenarios and see for which wall boost factors the NLO friction is of the same order for symmetry restoring and symmetry breaking transitions.

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

bubbles_talk_18_v_1.pdf

15:30 Explaining the PTA signal and dark matter with a conformal dark sector

Strong first-order phase transitions offer a compelling explanation for the stochastic gravitational wave background in the nano-Hertz range measured by pulsar timing arrays (PTA). In this talk, I will consider a classically conformal dark sector in which the breaking of a dark U(1) gauge symmetry gives rise to a gravitational wave background that can fit the PTA data and additionally sources the mass of a stable fermionic sub-GeV dark matter candidate. The model is coupled to the Standard Model via a dark photon mediator which is tightly constrained by laboratory searches. I will discuss these accelerator constraints as well as cosmological constraints coming from the decay of dark Higgs bosons after the phase transition. Finally, I will present the results of a global fit and show that the model has viable parameter space where it fits the PTA data, reproduces the observed relic abundance and avoids all relevant constraints.

Speaker: Carlo Tasillo (None)

2025_09_24_DESY_theory_workshop.pdf

16:00 Coffee break

16:30 Paths Through the Dark: Comparing Approaches for Cosmological FOPTs

We explore the dynamics of cosmological phase transitions in a dark sector model featuring a dark photon associated with a U(1)D gauge symmetry and radiative symmetry breaking. Our analysis focuses on different approaches to construct the effective potential: the high-temperature approximation, a full numerical evaluation of the thermal integrals, and a dimensionally reduced 3D effective theory built with DRalgo, at both leading and next-to-leading order. We as well explore the effect of including the running of the parameters in order to respect the hiercarchy scales.
We investigate how these methods impact the characterization of the phase transition, particularly in the supercooled regime.
Our results show the importance of method choice when predicting observable signatures, and establish a benchmark for future studies of first-order phase transitions in models with weakly coupled dark sectors.

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

Daisy25.pdf

16:48 Non-singular solutions to the Boltzmann equation with a fluid Ansatz

Cosmological phase transitions can give rise to intriguing phenomena, such as baryogenesis or a stochastic gravitational wave background, due to nucleation and percolation of vacuum bubbles in the primordial plasma. A key parameter for predicting these relics is the bubble wall velocity, whose computation relies onsolving the Boltzmann equations of the various speciesalong the bubble profile. Recently it has been shown that an unphysical singularity emerges if one assumes these local quantities to be described as small fluctuations on a constant equilibrium background. I'll show that a way to solve this issue is by including the spatial dependence of the background into the Boltzmann equations for the particles distribution functions. We apply this formalism to the Standard Model with a low cutoff and find that stable deflagration solutions are found for almost all the values of the cutoff considered, while detonations are restricted to some corner of the parameter space.

Speaker: Enrico Perboni (T (Cosmology))

DESY_theory_workshop.pdf

17:06 Bubble wall dynamics from nonequilibrium QFT

First-order phase transitions (FOPT) in the early universe are a unique probe of physics beyond the Standard Model, playing a key role in electroweak baryogenesis and many different phenomena. Future gravitational wave detectors will allow us to see the signature of possible FOPT, but to extract theoretical value from it, we need a precise understanding of their dynamics. In this talk, I demonstrate how the language of non-equilibrium quantum field theory, together with the two-particle-irreducible effective action, offers a natural framework to describe the dynamics of a bubble after nucleation.
The arising picture captures all relevant fluid dynamics and quantum effects, thus unifying the existing frameworks for studying the bubble wall dynamics in all velocity regimes.

Speaker: Matthias Carosi (TUM)

Bubble_wall_dynamics___DESY_2025.pdf

14:00 → 17:30 Parallel Sessions Wednesday Pheno 1

14:00 Derivation of Super-Leading Logarithms in t-tbar Production

So far the appearance of super-leading logarithms in hadron-hadron collisions was only studied for massless states. We extend the formalism to include massive final states and derive the anomalous dimension. We find the presence of an additional phase and discuss its physical significance and the difference to the massless case.

Speaker: Josua Scholze (JGU Mainz)

Derivation of Super-Leading Logarithms in t-tbar Production_Desy.pdf

14:15 Effects of Super-Leading Logarithms in t-tbar Production

We investigate the effects of a new source of Super-Leading Logarithms in $t \bar{t}$-production at hadron colliders. We show how large logarithms arise from an additional imaginary contribution to the anomalous dimension associated with massive final states, and discuss their resummation. We analyze the numerical impact in partonic scattering processes and examine the behavior near threshold.

Speaker: Romy Grünhofer (Johannes Gutenberg-Universität Mainz)

DESY_2025_Grünhofer.pdf

14:30 Decoherence effects in entangled fermion pairs at colliders

Recent measurements at the Large Hadron Collider have observed entanglement in the spins of $t\bar{t}$ pairs. The effects of radiation, which are expected to lead to quantum decoherence and a reduction of entanglement, are generally neglected in such measurements. In this work we calculate the effects of decoherence from various different types of radiation for a maximally entangled pair of fermions -- a bipartite system of qubits in a Bell state. We identify the Kraus operators describing the evolution of the open quantum system with the integrated Altarelli-Parisi splitting functions.

Speaker: Rafael Aoude

Aoude_DESY_2025.pdf

14:45 Invariant-Mass Threshold Resummation for Four Top-Quark Production at the LHC

The production of four top quarks is one of the rarest processes in the Standard Model, and it was finally observed in 2023 at the LHC. Studying this process offers valuable insights into the top-Higgs interaction and may reveal new physics. Thus, comparing theoretical predictions with current and future measurements is a crucial test for the Standard Model.
In this talk, I will present the most accurate QCD predictions to date for $t\bar{t}t\bar{t}$ production, obtained using invariant-mass threshold resummation at NLL' accuracy, matched to NLO. I will discuss results for both the total cross section and the invariant-mass distribution, highlighting their significance and the improvements made.

Speaker: Michele Lupattelli (University of Münster)

Lupattelli_DESY_24Sep_2025.pdf

15:00 Born-projected leptons in Drell–Yan final state analysis

In the study of the Drell-Yan process with LO decay into leptons, the cross-section allows for an angular decomposition in terms of spherical harmonics in the Collins-Soper frame. This decomposition is particularly useful for fitting the experimental data to obtain measurements for each individual angular coefficient. These coefficients can then be used to extract physical observables, one of these is proportional to the forward–backward asymmetry, $A_{FB}$, which is the observable used in experiments to determine the effective weak-mixing angle, $\sin^2{\theta_{\rm eff}^\ell}$. However, this decomposition is not necessarily valid beyond LO. I will discuss how one can study more complicated final states (such as QED final-state radiation) by defining Born-projected leptons, allowing us to preserve the angular decomposition in terms of suitable generalised Collins-Soper angles. This is crucial for properly fitting the experimental data when the desired precision is comparable with higher-order QED contributions, and in particular would allow to extract the FB asymmetry from the angular coefficient beyond LO.

Speaker: Roger Balsach Garcia Cascon (T (Phenomenology))

DESYTW2025.pdf

15:15 Electroweak double-box integrals for Møller scattering with three Z bosons

In this work, we have computed the planar and non-planar contributions to the Møller scattering with three massive $Z$ bosons exchanged between the fermion lines. These cases involve complicated geometries like curves of genus $2$ and $K3$ surfaces, which until recently remained inaccessible. We demonstrate how these can be tamed with a newly developed technique for $\varepsilon$-factorization of Feynman Integrals.

Speaker: Dmytro Melnichenko (JGU Mainz)

synergies2025_dmelnichenko.pdf

15:30 Parton-shower and fixed-order QCD effects in weak-boson fusion and H → bb̄ decay

In this talk I will discuss differential theoretical predictions for Higgs-boson production in weak-boson fusion and its subsequent decay $H\to b\bar{b}$.

The distinct kinematics of weak-boson fusion allow us to suppress QCD backgrounds by imposing appropriate event selection criteria. However, it was recently observed that in fixed-order calculations these strict event selection criteria lead to large corrections - ~ -40% at NNLO in comparison to LO - with an apparent lack of perturbative convergence. One prominent source of such large effects is the tendency of the QCD radiation in the $H\to b\bar{b}$ decay to reduce the transverse momentum of b-jets to the point where they no longer pass the b-jet selection criteria.

I will show that these large kinematic effects are caused primarily by soft and collinear QCD radiation in the $H\to b\bar{b}$ decay subprocess and that they can be accounted for by using a parton shower. I will present NNLO-accurate predictions for the combined process $pp\to H(\to b\bar{b})jj$, where the $H\to b\bar{b}$ decay subprocess is matched to the Pythia parton shower using the MiNLO method. In comparison with purely fixed-order calculations the consistency of theoretical predictions is dramatically improved. The remaining theoretical uncertainty is of order 5-7%, primarily due to modelling of the differential $H\to b\bar{b}$ distributions.

Speaker: Dr Ivan Novikov (KIT)

slides.pdf

16:00 Coffee break

16:30 Alignment limit and strong first-order electroweak phase transition in extended Higgs sectors

In the alignment limit of extended Higgs sectors the couplings of one of the neutral Higgs bosons of the model are exactly equal to the couplings of the Higgs boson of the Standard Model at lowest order.
Using the different Yukawa types of a Two-Higgs doublet model as an example and taking into account all relevant experimental and theoretical constraints, it is analysed to what extent the parameter region close to the alignment limit is correlated with the parameter region giving rise to a strong first electroweak phase transition in the early universe. Prospects for probing these parameter regions at future runs of the LHC and future gravitational wave observatories will be discussed.

Speaker: Debankana Nath

Presentation_Debankana.pptx

PresentationPDF_Debankana.pdf

16:45 CP-violation in complex-singlet extension of 2HDM

We explore the possibility of CP-violation in the complex-singlet extension of 2HDM. The addition of complex singlet paves the way for additional sources of CP-violation compared to 2HDM. If a Z2-symmetry is imposed on the complex-singlet, it can accommodate a dark matter candidate as well. We identify the regions of parameter space, that can fit DM observables and at the same time generate sufficient CP-violation. The amount of CP-violation gets severely constrained from electric-dipole moment experiments, which we take into account. We also consider all existing theoretical and experimental bounds on the model parameter space. Finally, we probe the CP-violation in this model at future collider experiments.

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

talk_CPV_desy_theory_JayitaLahiri.pdf

17:00 Observable Optimization for Precision Theory: Machine Learning Energy Correlators

The practice of collider physics typically involves the marginalization of multi-dimensional collider data to uni-dimensional observables relevant for some physics task. In any cases, such as classification or anomaly detection, the observable can be arbitrarily complicated, such as the output of a neural network. However, for precision measurements, the observable must correspond to something computable systematically beyond the level of current simulation tools. In this work, we demonstrate that precision-theory-compatible observable space exploration can be systematized by using neural simulation-based inference techniques from machine learning. We illustrate this approach by exploring the space of marginalizations of the energy 3-point correlator to optimize sensitivity to the the top quark mass. We first learn the energy-weighted probability density from simulation, then search in the space of marginalizations for an optimal triangle shape. Although simulations and machine learning are used in the process of observable optimization, the output is an observable definition which can be then computed to high precision and compared directly to data without any memory of the computations which produced it

Speaker: Dr Arindam Bhattacharya (DESY)

DESY_th_2025.pdf

14:00 → 17:30 Parallel Sessions Wednesday Pheno 2

14:00 Renormalisation of Chiral Gauge Theories with Non-Anticommuting $\gamma_5$ in the BMHV Scheme at the 4-Loop Level

The renormalisation of chiral gauge theories such as the electroweak Standard Model inevitably leads to the well-known $\gamma_{5}$-problem. A mathematically rigorous approach is provided by the Breitenlohner-Maison/'t Hooft-Veltman (BMHV) scheme within dimen-sional regularisation (DReg), where full anti-commutativity of $\gamma_5$ is abandoned. This scheme, however, explicitly breaks gauge and BRST invariance, necessitating its systematic restoration via symmetry-restoring counterterms. In this talk, I report on recent progress in extending this renormalisation programme to higher loop orders. Most notably, we have completed the full 4-loop renormalisation of an Abelian chiral gauge theory, including the explicit construction of all required counterterms, yielding a finite and BRST-invariant theory up to this order. The renormalisation of this toy model demonstrates the practical feasibility of the BMHV scheme for fully automated higher-order calculations and provides a validation of our newly developed computational setup. The results will be published soon. Using the same computational methods, we are currently working on the renormalisation of the Standard Model at the 1- and 2-loop level within the BMHV scheme. In this context, the fate of the vector-like nature of QED and QCD within the BMHV framework and the associated role of evanescent gauge interactions is discussed. Some time ago we published a study that particularly focused on the impact of such evanescent details, including the treatment of fermions in $D$ dimensions. Ultimately, a renormalisation procedure with a self-consistent treatment of $\gamma_5$ will be essential for high-precision calculations of electroweak observables.

Speaker: Matthias Weißwange (TU Dresden)

DESYTheoryWorkshop_Matthias_Weisswange.pdf

14:15 Non-Abelian aspects of chiral gauge theories in the BMHV scheme at two-loop order

We discuss the full two-loop renormalization of a chiral gauge theory for non-anticommuting $\gamma_5$ at the example of a Non-Abelian toy model. We employ the BMHV scheme which trades the computational comfort of DReg calculations for consistency at arbitrary order. Crucially, BRST symmetry is spuriously broken and must be restored. We carry through the renormalization despite such obstructions and obtain the complete set of symmetry-restoring counterterms. This study falls into line with our previous efforts and presents the first multiloop calculation for the Non-Abelian case.

Speaker: Paul Kühler (TU Dresden)

BMHV_NAbelian.pdf

14:30 On-shell renormalization of vector-like leptons

Through tree-level mixing, vector-like leptons (VLL) can have a significant impact on the SM lepton mass generation, Higgs couplings and flavor (violating) observables. Precise predictions of these observables however require calculations beyond leading order, which necessitates the definition of a renormalization scheme.

In this talk, I present such a scheme, implementing on-shell conditions on the self-energies for the first time. I show how loop corrections to the mixing can be treated in a practicable way and discuss the impact of higher order corrections on observables, focusing in particular on the correlation between the g-2 and Higgs coupling of the muon, that serves as an important constraint on the VLL.

Speaker: Kilian Moehling (TU Dresden IKTP)

2509DESY-moehling.pdf

14:45 Effective Field Theories for Higgs Sector Extensions - when SMEFT is not enough

We integrate out the heavy scalar mass eigenstate in a real Higgs singlet extension of the Standard Model (SM) at one-loop order, taking into account full mixing between the BSM singlet and the SM-like Higgs fields. We highlight subtleties in the renormalization of the effective theory. We discuss the choice of a proper decoupling limit and whether the resulting effective Lagrangian is of SMEFT or HEFT type. Finally, we validate convergence of predictions from the effective theory to the full theory result for a chosen set of electroweak precision observables.

Speaker: Sebastian Schuhmacher (University of Freiburg)

DESYTheoryWorkshop2025.pdf

15:00 Characterising New Resonances at the LHC in EFT: Hints about SU(2) nature in extended scalar sectors

In theories with extended scalar sectors, e.g. when including a scalar mediator to a dark sector, the lightest new scalar degree of freedom might be accessible at colliders. Going beyond simplified models, such a theory can be described in a gauge-invariant way via an EFT with a non-linearly realised electroweak symmetry. In this generalised HEFT, depending on the SU(2) nature of the new scalar, operators arise at different orders. For instance, while an SU(2) doublet can couple to fermions at dim-4 via a Yukawa-like term, a singlet requires a Higgs insertion to make the coupling term gauge invariant, the operator experiencing an additional suppression. We use dimensional analysis to systematically evaluate expected hierarchies between Wilson coefficients, leading to structural relations between potential LHC observables, such as di-boson resonance, tau pair production or the di-photon channel. Should some hint of a new scalar field be observed, this analysis will help interpret it with respect to possible UV models.

Speaker: Maya Hager (Max-Planck Institute fuer Kernphysik, Heidelberg)

Hager_DesyTheory2025.pdf

15:15 Higher-Spin Dark Matter Meets Hilbert Series: Counting Interactions to Even Higher Orders

An effective Lagrangian is composed of all higher dimensional operators that are Lorentz singlets and invariant under the gauge symmetries of the theory, suppressed by powers of the cutoff. A challenging problem is the construction of the EFT operators, since the number of possibilities grows extremely fast. Furthermore, many of these operators are linearly dependent or can even be discarded, through field redefinitions which make use of equations of motion (EOM) or integration by parts (IBP). Therefore, the number of independent operators of a certain type at some order in an EFT is an extremely useful information, and it turns out one can obtain it precisely by employing the Hilbert Series, a tool from Invariant Algebra that allows one to count invariants in an EFT. In this work, we perform the operator counting of the EFT of the Standard Model aided with a higher-spin Dark Matter particle, up to mass dimension 12."

Speaker: Mr Bruno Eduardo (University of São Paulo)

DESY theory workshop - presentation.pdf

16:00 Coffee break

16:30 How common are Grand Unified Theories?

The individual fermion generations of the Standard Model fit neatly into a representation of a simple Grand Unified Theory gauge algebra. If Grand Unification is not realized in nature, this would appear to be a coincidence. We attempt to quantify this coincidence.
We find that only a small fraction of consistent fermion representations similar to the Standard Model are unifiable when the analysis is extended beyond the immediate neighborhood of the single-generation Standard Model. This purely group-theoretical analysis may be taken as a bottom-up indication for Grand Unification, conceptually similar to a naturalness argument.

Speaker: Johannes Herms (Kavli IPMU, University of Tokyo)

250924DESYpGUT.pdf

16:45 Symmetry Breaking on 5D Orbifolds and Application to GUTs

Extra-dimensions are a very interesting tool to address various missing parts of the Standard Model of particle physics. When one extra-dimension is added, a compactification based on a orbifold is required to ensure a chiral spectrum for the fermions. It also allows mechanisms to consistently break the bulk gauge group. Symmetry breaking on orbifolds can be understood in two different ways: through the boundary conditions imposed on the fields by the orbifold structure or through the vacuum structure of the fifth component of the gauge fields, the "gauge-scalar". We will use those mechanisms to build consistent 5D GUTs. We will focus on theories featuring an asymptotic behaviour for the running of the gauge couplings, dubbed asymptotic GUTs (aGUTs).

Speaker: Wanda Isnard (IP2I, Lyon University)

DESY_theory_workshop__2025_.pdf

17:00 Renormalizability and UV behavior of 5D gauge theories

The idea of supplementing the number of spacetime dimensions has long been deemed as one of the potential extension of the Standard Model, as it provides powerful tools to explain some of its shortcomings. One example of higher-dimensional formulations are asymptotic grand unified theories (aGUTs), for which the couplings do not meet at a high scale, but instead flow together towards a fixed point in the UV. Although the higher-dimensional dynamics push the theories into a nonpertubatively renormalizable regime, they can be thought of as fundamental in the context of the asymptotic safety scenario. Using these techniques, we focus on five-dimensional gauge theories and check the existence of fixed points, thus ensuring a good behavior in the UV. Additionally, the presence of both bulk and localized divergencies is investigated, with the purpose of shedding light on the renormalization status of such theories.

Speaker: Anca Preda (Lund University)

DESY_workshop.pdf

14:00 → 17:30 Parallel Sessions Wednesday String

14:00 Cluster Algebraic letters 5- and 6-point QCD processes

By breaking dual conformal invariance, we transform cluster-algebraic predic-
tions for the alphabet of 9-point amplitudes in N = 4 super Yang-Mills theory to analogous
predictions for 5- and 6-point processes in QCD. We start by obtaining, for the first time,
candidate letters for 6-point processes with one massive external leg, and confirm that
they essentially contain those of all 1-loop integrals with these kinematics. Taking the
limit where the massive leg becomes massless, we then reproduce the 167 letters recently
argued to suffice for the finite part of planar 2-loop amplitudes for 6-point massless QCD
processes, and further predict another 14 letters that might appear at higher loops. Similarly,
we analyse the 5-point 2-mass case, where we manage to match with almost all known letters known by direct Feynman Integral computations. Finally, we comment on positivity properties of these letters.

Speaker: Rigers Aliaj (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

Aliaj_DESY_Theory.pdf

14:15 Duality symmetries and integrable deformations of dimensionally reduced GR

The Kaluza-Klein (KK) reduction of pure $D=4$ GR along two commuting Killing isometries is well known to provide an effective $D=2$ integrable field theory. This is profoundly connected to the existence of hidden, infinite dimensional symmetries arising upon toroidal KK reductions of gravity to $D=2$. In this talk, I will show how to exploit the power of such symmetries in order to prove the integrability of a certain class of deformations of the $D=2$ model, based on the introduction of auxiliary fields. I will then comment on their possible uplifts to $D=4$.

Speaker: Mattia Cesaro (Max Planck Institute for Gravitational Physics (AEI))

Gravity_deformations.pdf

14:30 Vacua, Symmetries, and Higgsing of Chern-Simons Matter Theories

In supersymmetric theories, an object of great interest is the moduli space of vacua, parameterised by the VEVs for the scalars in the various supermultiplets and endowed with a strict geometric structure, which factorises into the so-called maximal branches and encodes the generalised Higgs mechanism.
In this talk, I will explore the moduli space of 3d N=3 and N=4 Chern–Simons-matter theories realised via Type IIB brane setups. For N=4 theories with CS level 1, SL(2,Z) dualisation yields CS-free duals, allowing for a complete analysis of the moduli space through already studied models. For N=4 theories with higher CS levels, where this approach is not applicable, I will probe the moduli space of vacua by introducing two auxiliary theories, known as magnetic quivers, that capture the maximal branches of the original theory and enable the study of their RG flows. In the N=3 case, I will extend the magnetic quiver prescription to each maximal branch, providing the first comprehensive picture of their moduli spaces, both in the Lagrangian and in the non-Lagrangian case.

Speaker: Dr Fabio Marino (University of Vienna)

Presentation_CSM_Theories_DESY.pdf

14:45 Bubbles in AdS

Considering a CFT dual to the quartic theory in AdS, we used the analytic bootstrap techniques, to find a piece of the anomalous dimensions of double trace operators corresponding to bubble diagrams in AdS at every loop order solely reconstructed from the tree-level data. We then illustrated a relation between these pieces and the iterated unitarity cuts of AdS amplitudes. The work is in progress.

Speaker: Mohammad Reza Khansari (SISSA)

Bubbles in AdS.pdf

15:00 Feynman integrals beyond Polylogarithms

Feynman integrals whose associated geometries extend beyond the Riemann sphere, such as elliptic and Calabi–Yau, are increasingly relevant in modern precision calculations. They arise not only in next-to-next-to-leading order (NNLO) corrections to collider cross-sections but also in the post-Minkowskian expansion of gravitational wave scattering. A powerful approach to compute such integrals is via differential equations, particularly when cast in canonical form, which simplifies their ε-expansion and makes analytic properties manifest. In this talk, I will present a method to systematically construct canonical differential equations even for integrals that evaluate beyond multiple polylogarithms, including elliptic and Calabi–Yau, highlighting its utility in both quantum field theory and gravitational physics.

Speaker: Sara Maggio (Bonn University)

Desy Theory Workshop.pdf

15:15 Non-Invertible Symmetries and Dp-Branes in 2D Compact Boson CFTs

We investigate non-invertible symmetries in non-linear sigma models in terms of the self-dual momentum lattice. We first recast the well-known T-duality of the $c=1$ compact boson, which results in the exchange of D0- and D1-branes, in lattice terms. We then move to the toroidal case, which is characterised by a richer duality group and a larger spectrum of Dp-branes, analysing how the introduction of twisted sectors, required for modular invariance after gauging, leads to new Ishibashi states.

Speaker: Giacomo Maggiorotti (University of Bologna)

Non-Invertible Duality Defects and Lattice Symmetries in 2D c=2 CFTs.pdf

15:30 High-Precision Analytic Continuation of Multivariable Hypergeometric Functions and Prospects for Feynman Integral Evaluation

We present a high-precision numerical approach for evaluating multivariable hypergeometric functions with parameters linearly dependent on the dimensional regularization variable ε. The method is based on constructing analytic continuations via Frobenius-type generalized series solutions of associated Pfaffian systems. Implemented in the PrecisionLauricella package, this technique achieves high numerical accuracy while remaining computationally efficient and parallelizable. Importantly, the same algorithmic framework can be directly applied to a wide class of Feynman integrals that satisfy similar differential systems. This opens the path toward high-precision ε-expansion of Feynman integrals using the same continuation and reconstruction techniques developed for hypergeometric functions.

Speaker: Maxim Bezuglov (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

Hypergeometry_Bezuglov.pdf

15:45 Bootstrapping Gukov-Witten defects in N=4 SYM

I will discuss Gukov-Witten surface defects in N=4 Super Yang-Mills from the point of view of the analytic conformal bootstrap. These defects are defined by the singular behaviour of the gauge and scalar fields along a surface. After reviewing a recently derived conformal dispersion relation, I will show how to bootstrap the two-point functions of bulk operators in presence of a surface defect.

Speaker: Davide Bonomi (T (Stringtheory))

slide_bonomi.pdf

16:00 Coffee break

16:30 Positivity properties of five-point two-loop Wilson loops with Lagrangian insertion

I will discuss the geometric integrand expansion of the pentagonal Wilson loop with a Lagrangian insertion in maximally supersymmetric Yang-Mills theory. I will focus on the integrand corresponding to an all-loop class of ladder-type geometries, and then investigate the known two-loop observable from this geometric viewpoint. To do so, we evaluate analytically the new two-loop integrals corresponding to the negative geometry contribution, using the canonical differential equations method. Inspecting the analytic result, we present numerical evidence that in this decomposition, each piece has uniform sign properties, when evaluated in the Amplituhedron region. Finally, I will report the recent progress of bootstrap approach for the ladder-type geometries based on geometric Landau analysis, which determines which singularities are actually present in the integrals. We successfully implement this procedure and compute the six-point two-loop and five-point three-loop ladder negative geometries at the symbol level. We found that five-point ladder geometries involve novel pentagon alphabet letters, which also appear in planar three-loop Feynman integrals.

Speaker: Shun-Qing Zhang (Max Planck Institute for Physics)

DESY_zhang.pdf

16:45 One-loop string scattering amplitudes at finite $\alpha’$

String theory provides us with UV-finite amplitudes of quantum gravity at every order in perturbation theory. However, explicit computations become quickly very complicated, to the point that their evaluation have been possible only in the low- and high- energy expansion. Essentially no results are known at intermediate values of $\alpha’$.

In addition to that, the starting set up of this computations is Euclidean, and analytic continuation to the Lorentzian theory requires the implementation of the $i\varepsilon$ prescription in string theory, which, while conceptually understood, it is in general technically difficult to perform.

In this talk, I will present a novel technique to evaluate one-loop amplitudes at finite $\alpha’$, which also implements the i \epsilon prescription in string theory. Such technology opens a window for computations that were previously inaccessible.

Based on https://arxiv.org/abs/2501.13827 and other unpublished results.

Speaker: Marco Maria Baccianti (University of Amsterdam)

Talk Hamburg pdf.pdf

17:00 Establishing the relation between instantons and resonant states

Schrödinger-type eigenvalue problems are ubiquitous in theoretical physics, with quantum-mechanical applications typically confined to cases for which the eigenfunctions are required to be normalizable on the real axis. However, seeking the spectrum of resonant states for metastable potentials or comprehending $\mathcal{PT}$-symmetric scenarios requires the broader study of eigenvalue problems for which the boundary conditions are provided in specific angular sectors of the complex plane. We generalize the conventional path integral treatment to such nonstandard boundary value problems, allowing the extraction of spectral information using functional methods. We find that the arising functional integrals are naturally defined on a complexified integration contour, encapsulating the demanded sectorial boundary conditions of the associated eigenvalue problem. The attained results are applied to the analysis of resonant ground-state energies, through which we identify the previously elusive one-to-one correspondence between decay rates derived from real-time quantum tunneling dynamics and those obtained via the Euclidean instanton method.

Speaker: Nils Wagner (Technical University of Munich)

DESY_Wagner.pdf

17:30 → 18:30 Hertz Lecture

17:30 Hertz Lecture: Visible and Invisible in fundamental physics and art

Speaker: Michelangelo Mangano

Mangano-Hertz.pdf

19:00 → 21:30 Workshop Dinner

Thursday 25 September

09:00 → 11:00 Plenary Session Thursday I

09:00 Challenging the lore on the strong CP problem

Speaker: Carlos Tamarit

Tamarit_DESY_TH_2025.pdf

09:40 Electroweak Phase Transitions, Gravitational Waves, and Electroweak Baryogenesis

Speaker: Lisa Biermann

lisa_biermann_desy_theory_workshop.pdf

10:20 CP violation in the Standard Model and Beyond

Speaker: Aleksei Rusov

CP-violation-Rusov.pdf

11:00 → 11:30 Coffee break

11:30 → 12:50 Plenary Session Thursday II

11:30 Muon g-2: SM Theory status

Speaker: Gilberto Colangelo

g-2_DESY-2025.pdf

12:10 Open Quantum Systems as Detectors

In this talk, I will highlight the advantages of quantum sensors in probing motivated regions of paramter space that remain inaccessible to classical detectors. I will focus on table-top atom interferometers, many of which are already operating on Earth, and their potential to track interactions with particles in the environment by using the quantum properties of coherence and decoherence. In particular, I will discuss how sub-GeV dark matter is especially well-suited for detection with these devides. I will also show how coherently enhanced decoherence could be tested experimentally in the laboratory and outline additional phenomenological applications.

Speaker: Clara Murgui Galvez

DESYth.pdf

12:50 → 14:00 Lunch

14:00 → 18:00 Parallel Sessions Thursday Cosmo 1

14:00 Asymgenesis

I present a new framework—Asymgenesis—that connects the baryon asymmetry of the universe to the dark matter density within the standard type-I seesaw model. The mechanism starts from a primordial charge asymmetry, either in the visible or dark sector, and redistributes it via a higher-dimensional portal operator. This process generates both a nonzero $B-L$ asymmetry and an asymmetric dark matter component.

Unlike conventional ADM scenarios, Asymgenesis places minimal demands on the portal interaction: it need not violate $B-L$, and the scales of $B-L$ violation and charge transfer can be separated. This enhances flexibility and broadens the model-building landscape for ADM

Speaker: Sascha Weber (JGU Mainz)

Sascha_Weber_Asymgenesis.pdf

14:18 Thermal Effects in Particle Production

In this talk, we explore the role of non-equilibrium dynamics within a thermal plasma in the context of processes in the early Universe and astrophysical environments. Our approach is based on one-particle-irreducible (1PI) resummed propagators computed within the real-time formalism of thermal field theory, allowing us to consistently include thermal masses, widths, and other non-trivial plasma effects. Notably, we account for multiple soft scatterings with the thermal medium, described by the Landau-Pomeranchuk-Migdal (LPM) effect, which can significantly alter particle production rates. We discuss the implications of these corrections for the accurate prediction of particle abundances in cosmological and astrophysical settings, e.g., in the context of freeze-in production of scalar dark matter.

Speaker: Maria Jose Fernandez Lozano (JGU Mainz)

DESY25_Maria.pdf

14:36 A portal to the SM for resonant SIMPS

Strong Interacting Massive Particles are a well motivated DM candidate. In particular we took into consideration a QCD-like theory with three flavours, where the DM candidate is a dark pion. In Ref[2405.10367], it has been found that a non-vanishing theta angle would trigger resonant processes which would give rise to the observed relic density, together with providing velocity dependent self-interactions without a light mediator. In this work, we studied its interactions with SM particles in the case of a dark photon portal, focusing on the thermalizations and the stability issues of the dark pions. In the scenario we considered, a dark pion mass in the window of 10-50 MeV would be consistent with all bounds, and would explain successfully astrophysical observations in the context of SIDM.

Speaker: Luca Marsili (IFIC-University of Valencia)

SIMPS_DESY.pdf

14:54 Primordial Leptogenesis

We propose a novel realization of Dirac leptogenesis by sourcing the required lepton asymmetry via inflationary dynamics. In particular, an asymmetry is generated in the scalar sector of the model during the reheating phase and is then transferred to the leptonic sector via Yukawa interactions and subsequently to a baryon asymmetry via weak sphaleron processes. The current scenario also offers a natural explanation for the smallness of the light neutrino masses, in agreement with current experiments.

Speaker: Juan Pablo Garces (Max Planck Institut fur Kernphysik)

DESY_slides_Garces.pdf

15:12 Dirac Leptogenesis Via Scattering

We study the possibility of generating matter-antimatter asymmetry in the early Universe before the Electroweak phase transition by considering three Dirac right-handed neutrinos in addition to the standard model particles using the CTP formalism. In addition, we consider two off-shell heavy scalars, so the temperature of the Universe is never required to be high enough after inflation to take them on-shell. We focus on 2 by 2 scattering processes mediated through these heavy scalars where right handed neutrinos go out of the equilibrium generating lepton asymmetry which is then converted to baryon asymmetry using sphaleron processes and the results for baryon to photon ratio are compared to the observational values as obtained from Planck Mission to put experimental constraints on these models.

Speaker: Mr RAZA UR REHMAN MIR (TUM)

DiracLepto_Present_DESY_Sep25_RazaMir.pdf

15:30 Detecting Ultralight Dark Matter with Matter Effect

Ultralight particles, with a mass below the electronvolt scale, exhibit wave-like behavior and have arisen as a compelling dark matter candidate. A particularly intriguing subclass is scalar dark matter, which induces variations in fundamental physical constants. However, detecting such particles becomes highly challenging in the mass range above $10^{-6}\,\text{eV}$, as traditional experiments face severe limitations in response time. In contrast, the matter effect becomes significant in a vast and unexplored parameter space. These effects include (i) a force arising from scattering between ordinary matter and the dark matter wind and (ii) a fifth force between ordinary matter induced by the dark matter background. Using the repulsive quadratic scalar-photon interaction as a case study, we develop a unified framework based on quantum mechanical scattering theory to systematically investigate these phenomena across both perturbative and non-perturbative regimes. Our approach not only reproduces prior results obtained through other methodologies but also covers novel regimes with nontrivial features, such as decoherence effects, screening effects, and their combinations. In particular, we highlight one finding related to both scattering and background-induced forces: the descreening effect observed in the non-perturbative region with large incident momentum, which alleviates the decoherence suppression. Furthermore, we discuss current and proposed experiments, including inverse-square-law tests, equivalence principle tests, and deep-space acceleration measurements. Notably, we go beyond the spherical approximation and revisit the MICROSCOPE constraint on the background-induced force in the large-momentum regime, where the decoherence and screening effects interplay.

Speaker: Xucheng Gan (T (Cosmology))

DESY_Theory_Workshop_2025.pdf

16:00 Coffee break

16:30 Prospects and Limitations of PTA Anisotropy Searches

Anisotropies play a central role in distinguishing between a cosmological or astrophysical origin of the nanohertz gravitational wave background, as detectable anisotropies are expected for a GWB from a population of supermassive black hole binaries but not for cosmological sources.
We analyze prospects for detecting anisotropies from either bright single sources or large scale anisotropies with frequentist methods by simulating complete pulsar timing array datasets for both current and expected future PTA configurations. From this, we identify the most promising search strategies, derive fundamental limits of frequentist anisotropy searches and set realistic expectations for near-future anisotropy detection prospects.

Speaker: Anna-Malin Lemke (T (Cosmology))

16:48 Did IceCube detect Dark Matter around Blazars?

Blazars are a subclass of active galactic nuclei (AGN), the brightest continuously emitting sources in the Universe, powered by accreting supermassive black holes (SMBH). Their defining characteristic is the presence of powerful, back-to-back relativistic jets of protons and electrons, with one jet closely aligned in the direction of Earth. This offers a unique opportunity to probe physics Beyond the Standard Model. The jet can in fact interact with the surrounding Dark Matter in the host galaxy’s halo, where the presence of the SMBH induces a spike in density, offering compelling direct and indirect detection prospects. A key signature of this interaction is the production of high-energy neutrinos, as secondary products of the proton disintegrating in the collision. The resulting outgoing neutrino flux is qualitatively and quantitatively different from the one expected via Standard Model processes alone and, notably, provides a better fit to observations for a large region of unexplored light Dark Matter parameter space. This raises the intriguing question of whether high-energy neutrino observations from blazars could represent the first indirect detection of Dark Matter.

Speaker: Andrea Giovanni De Marchi (Università di Bologna and INFN)

De_Marchi_DESY.pdf

17:06 Photo- and Hadrodisintegration constraints on massive relics decaying into neutrinos.

In this talk, I will present a detailed study of the cosmological constraints on the decay of a relic particle into neutrinos, in particular those arising from the observed light-element abundances in the early Universe. I will focus on the late-time disintegration of the light elements previously synthesised during BBN. Several processes are relevant, including final-state radiation associated with the decay, as well as subsequent interactions of the injected neutrinos with the thermal background neutrinos or between themselves. All processes generically contribute to the production of electromagnetic and often also hadronic material and may therefore induce late-time photodisintegration and hadrodisintegration reactions, i.e. the destruction of light elements that have previously been formed during BBN. I will present a Monte-Carlo inspired probabilistic approach which we find more suitable than Boltzmann techniques, taking into account all of these different reactions as well as their interplay. The resulting constraints cover a broad range of previously unexplored masses and lifetimes of the relic source particle. Based on 2505.01492.

Speaker: Jonas Frerick (Sapienza University Rome)

slides_desy_bbn.pdf

17:24 High-Frequency Gravitational Waves from Phase Transitions in Nascent Neutron Stars

During a neutron star's formation in a supernova, its core may undergo a phase transition into deconfined quark matter. The phase transition would likely be first-order, proceeding by bubble nucleation. We show that such a phase transition would be accompanied by the emission of high-frequency gravitational waves (MHz band), which could be within reach of proposed gravitational wave detectors. Therefore, these detectors provide a unique opportunity for testing quantum chromodynamics in a high pressure and density regime that is otherwise theoretically and experimentally inaccessible.

Speaker: Katarina Bleau

desy_talk.pdf

17:42 Simulating axion electrodynamics near pulsars

It has been demonstrated that axions can generically copiously produced from fluctuations in the background electromagnetic fields of pulsars. For axions with masses in the range $10^{-9} \text{eV} \lesssim m_a \lesssim 10^{-4} \text{eV}$, a large fraction of axions sourced from this process will remain gravitationally confined near the surface of the star, accumulating on long timescales, forming dense axion clouds.

Here, I will discuss how the presence of a dense axion could can back-react on the electrodynamic processes responsible for the generation of observed radiation from neutron stars. I will present preliminary results from numerical simulations aimed at identifying new observational signatures in the electromagnetic spectrum of pulsars that can be used to constrain the axion parameter space.

Speaker: Anne Freise (University of Oxford)

DESY_Anne_Freise_powerpoint.pptx

DESY_theory_workshopV2.pdf

14:00 → 18:00 Parallel Sessions Thursday Cosmo 2

14:00 Gravitational production after inflation : Boltzmann and Bogoliubov approaches

In this talk, I consider spectator scalar fluctuations generated by gravity during inflation and reheating. This framework can be applied to the production of Dark Matter (DM) or Standard Model (SM) scalar degrees of freedom. I first review the perturbative approach describing gravitational portals from gravity EFT and solving the Boltzmann equation for the distribution function of scalar modes. Then, a non-perturbative Bogoliubov treatment is described and compared to the perturbative approach. In recent work, we obtained both long and short-wavelength spectra, highlighting that the spectral index in the IR regime varies depending on the post-inflationary equation of state (EoS) for a wide range of momenta and masses. In the UV regime, we identify high-frequency oscillations in the spectrum due to the inflaton background dynamics during reheating, which leads to interference. Remarkably, we found that for a large range of EoS, the spectral index in the UV is independent of the EoS. We corroborate our results by comparing the Bogoliubov treatment with perturbative methods, solving the Boltzmann equation. We show agreement across all EoS in the UV regime for the two approaches. Finally, we discuss the gravitational reheating scenario and address constraints from primordial gravitational wave overproduction, finding that successful gravitational reheating is achievable for sufficiently high EoS.

Speaker: Simon Clery (Technical University of Munich (TUM))

DESY2025_Clery.pdf

14:18 Insufficient Fermion Reheating in Quartic Inflaton Potentials

The transition between cosmic inflation to a phase of radiation domination, e.g. reheating, is an essential ingredient of any theory of inflation. The reheating stage is typically characterized by an inflaton oscillating about the minimum of its potential. Such dynamics, inducing the growth of inhomogeneities and non-perturbative dynamics have been shown to be relevant for a reheating stage achieved by coupling the inflaton field to bosons. However, the case of fermions remains insufficiently explored. We explore such possibility by considering a inflaton potential quartic about its minimum, known to trigger a significant growth of inhomogeneities resulting in the fast fragmentation of the inflaton condensate. We investigate, in conjuncture with the fragmentation process, the full non-perturbative production of fermions, accounting for a smooth transition from cosmic inflation to the reheating stage and by comparing with a more standard Boltzmann approach. In doing so we are able to demonstrate the insufficiency of fermions to reheat the Universe in quartic inflaton potentials even for large couplings, contrary to previous findings.

Speaker: Nabeen Bhusal (T (Cosmology))

Fermion (P)reheating in a Quartic Inflaton Potential.pdf

14:36 Evaporating Primordial Black Holes: Reformation and Isocurvature Perturbations

Primordial black holes (PBHs) lighter than 10^9 g are expected to have fully evaporated before the big bang nucleosynthesis, leaving their past abundances unconstrained by observations. Depending on their initial abundance, these PBHs could have temporarily dominated the Universe or remained as a subdominant component. In this talk, I explore the cosmological implications of such light mass PBHs. If they induced an early matter-dominated phase, the growth of initial PBH density perturbations could trigger collapse on horizon scales, leading to the formation of significantly heavier PBHs. These reformed PBHs survive beyond the evaporation of the original PBHs, and could give multi-messenger signatures observable today. Alternatively, if light mass PBHs never dominated the Universe, they can generate significant isocurvature perturbations due to their biased clustering and the branching ratio of their Hawking radiation. This can provide a novel avenue for observationally constraining their past abundances through cosmic microwave background constraints on the isocurvature perturbations.

Speaker: TaeHun Kim (Korea Institute for Advanced Study)

TaeHun_Kim_DESY_(15+3).pdf

14:54 Opening the Window for Ultra-Light Primordial Black Holes

We study the scalar-induced gravitational wave (SIGW) signal from the evaporation of primordial black holes (PBHs). In the idealised monochromatic case, a pronounced SIGW signal is produced via the Poltergeist mechanism, driven by a sudden transition from matter to radiation dominance. However, realistic extended mass distributions - such as those predicted by the Press-Schechter formalism from the collapse of superhorizon-scale over-densities - smoothen this transition, leading to a substantial suppression of the resulting GW signal. We show that this suppression not only renders much of the ultra-light PBH parameter space inaccessible to future GW experiments, but also allows these scenarios to evade stringent Big Bang nucleosynthesis constraints, thereby opening up new viable regions of parameter space.

Speaker: Nicholas Leister (JGU Mainz)

DESY_Leister.pdf

15:12 Axion dark matter from parametric resonance

In this work, we study the cosmological implications of an initial displacement of the Peccei-Quinn breaking field generated during inflation and the subsequent oscillations of the field around its minimum. These oscillations induce a parametric resonance effect, leading to the exponential growth of perturbations. In our analysis, we employ lattice simulations to investigate the abundance of axions produced by this resonance, as well as the formation and dynamics of the resulting topological defects.

Speaker: Riccardo Natale (T (Cosmology))

Axion dark matter from parametric resonance.pdf

15:30 News on Cold Baryogenesis: Baryon number violation from Standard Model SU(2)-textures induced by Higgs bubble collisions at T=0

The matter-antimatter asymmetry of the Universe represents one of the main open questions in particle physics and cosmology. In this talk, we will present a novel realization of cold baryogenesis, a mechanism involving the formation and decay of Standard Model SU(2)-textures, that relies on the out-of-equilibrium dynamics during a strong first order electroweak phase transition. By performing extensive lattice simulations of the Higgs doublet and gauge field dynamics, we evaluate the related Chern-Simons number production as well as the rate of baryon number violation, as a function of the parameters of the phase transition and the shape of the Higgs potential. We finally provide an estimate for the total baryon asymmetry generated this way.

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

Cataldi_DESYworkshop.pptx

16:00 Coffee break

16:30 The Supercool Audible Axion

We present the audible axion mechanism extended by a period of supercooling that delays the onset of axion oscillations.
While the original setup relies on a large axion decay constant and coupling to a dark Abelian gauge field to produce sizable gravitational wave signals, in this talk we discuss how supercooling opens up the testable parameter space and reduces the required coupling to $\alpha \gtrsim 1$.
We further showcase that the emission of gravitational waves via the axion coupling to the Standard Model photon becomes possible, generating a strong signal in the $\mu$Hz or ultra-high frequency range. The main limitation for this scenario results from Schwinger pair production.

Speaker: Christopher Gerlach (Johannes Gutenberg-Universität Mainz)

DESY_2025_Gerlach_Supercooled_audible_axion.pdf

16:48 Causality Bounds on the Primordial Power Spectrum

Effective field theories (EFTs) parametrize our ignorance of the underlying UV theory through their Wilson coefficients. However, not all values of these coefficients are consistent with fundamental physical principles. In this talk, I will talk about recent work where we explore the consequences of imposing causal propagation on the comoving curvature perturbation in the EFT of inflation, particularly its impact on the primordial power spectrum and the effective sound speed $c^{\mathrm{eff}}_s$. We investigate scenarios where $c^{\mathrm{eff}}_s$ undergoes a transition, remaining consistent with CMB constraints at early times but later experiencing a drastic change, becoming highly subluminal. Such scenarios allow the primordial power spectrum to grow at small scales, potentially leading to the formation of primordial black holes or the generation of scalar-induced gravitational waves. We find the generic feature that in a causal theory, luminal sound speeds imply a free theory, effectively constraining the dynamics. Additionally, we obtain that when considering natural values for the Wilson coefficients, maintaining the validity of the EFT and the weakly coupled regime, and enforcing causal propagation of the EFT modes, the power spectrum cannot increase drastically. This imposes significant constraints on the parameter space of models aiming to produce such features.

Speaker: Sebastian Cespedes (Imperial College London)

DesyCausality.pdf

17:06 Post-inflationary enhancement of adiabatic perturbations in modular cosmology

In this talk I will present a recent investigation where we show that multi-field inflationary models with negligible turning in field space during inflation can lead to an effective sourcing of adiabatic from entropic perturbations after the end of inflation. I will illustrate this general phenomenon with a detailed analysis of an inflationary model whose scalar potential is determined by modular invariance. Its entropic perturbations are frozen during inflation, but instead, they are converted into adiabatic ones in the first post-inflationary e-folds. Finally, I will show that the curvature power spectrum, giving rise to CMB fluctuations, reaches a novel and enhanced plateau and end up with a discussion on the implications on the inflationary observables As, ns and r.

Speaker: Rodrigo Gonzalez Quaglia (University of Groningen)

Rodrigo_DESY.pdf

17:24 $\Delta N_{eff}$ from SGWB: PTA and CMB

We investigate whether an Early-Universe stochastic gravitational–wave background (SGWB) can account for the common‐spectrum process reported by NANOGrav, while also being consistent with current and projected CMB measurements of extra radiation. We compute the contribution of the effective number of relativistic species, $\Delta N_{eff}$, for a number of Early-Universe models proposed to explain the pulsar timing array (PTA) spectrum. We demonstrate that models predicting $\Delta N_{eff}$ above the CMB limit would be firmly excluded, implying that the NANOGrav signal in tension with these bounds must instead arise from astrophysical sources. We find that current NANOGrav 15-year dataset, sensitive up to 60 nHz, gives a negligible contribution to $\Delta N_{eff}$ and remains well below the present and future CMB detection threshold. However, when we project future PTA capabilities reaching upto 1 $\mu$Hz, even with our conservative estimate we find that Inflation, Scalar Induced Gravitational Waves (SIGW), and metastable cosmic strings can induce a $\Delta N_{eff}$ large enough for $>3.5\sigma$ detection by the Simons Observatory.

Speaker: Amresh Verma (Ariel University)

DESY_Amresh_2025.pdf

17:42 A Possible Cosmological Origin of the KM3-230213A event

We propose a novel cosmological scenario to explain the exceptional KM3-230213A neutrino event reported at an energy scale of O(100) PeV by the KM3NeT collaboration, along with its associated gravitational wave signatures. In our framework, ultra-high-energy neutrinos originate from the decay of a super-heavy sterile neutrino produced via the Hawking evaporation of primordial black holes in the early Universe. While two sterile neutrinos in the model are responsible for generating light neutrino masses as required by oscillation data through the type-I seesaw mechanism, a third sterile neutrino or a heavy neutrino-like fermion with extremely feeble couplings can have a lifetime suitable for producing a neutrino flux consistent with the observed event. Furthermore, our scenario predicts two distinct GW signatures: one arising from gravitons emitted during PBH evaporation and another from the Bremsstrahlung process during the decay of the sterile neutrino. These complementary signals provide a multi-messenger probe of the underlying physics. Our results thus offer a compelling explanation for the KM3-230213A event and open new avenues for investigating the interplay between ultra-high-energy neutrino astronomy and ultra-high-frequency gravitational wave cosmology.

Speaker: Erdenebulgan Lkhagvadorj

DESY25_EB_Lkh.pdf

14:00 → 17:30 Parallel Sessions Thursday Pheno 1

14:00 Precise predictions for trilinear Higgs couplings and $gg\to HH$

Investigating the trilinear self-coupling of the discovered Higgs boson is one of the main goals of particle physics in the near and far future. At the same time the quest for the existence of Higgs-like self interactions also provides a unique possibility in the search for new physics. BSM states can modify the trilinear Higgs coupling at the classical- or quantum-level, or contribute resonantly to processes that are sensitive to its extraction (and combinations thereof). Gluon fusion into two SM-like Higgs bosons offers the most promising possibility to scrutinize and eventually disentangle such scenarios in the future.

In this talk, we will introduce the framework $\texttt{anyH3}$ which allows to compute trilinear scalar couplings at the full one-loop level in arbitrary renormalisable QFTs as well as its extension $\texttt{anyHH}$ providing fully differential predictions for $gg\to h_i h_j$. The latter incorporates corrections proportional to Higgs-BSM couplings at next-to-leading order to the resonant part of the process. We show that such corrections are crucial in BSM scenarios that feature an SM-like Higgs boson in exact or near alignment to the SM Higgs. Furthermore, we discuss different aspects of the renormalisation needed for a proper description of scalar self-interactions and showcase its importance for di-Higgs production.

Speaker: Martin Gabelmann (U. Freiburg)

desytheoryws25.pdf

14:15 Two-loop renormalisation of the 2HDM and phenomenological applications

Understanding the renormalisation structure of extended Higgs sectors at higher orders is essential for obtaining precise and reliable theoretical predictions. In this work, we focus on the renormalization of the two-Higgs-doublet model (2HDM), and present a consistent renormalisation scheme for its scalar sector at two loops. A particular emphasis is placed on the treatment of the mixing angles near the alignment limit, which is especially subtle and can have significant impact on physical observables. As a non-trivial application of our framework, we compute the leading two-loop corrections to the trilinear Higgs couplings $\lambda_{hhh}$ and $\lambda_{hhH}$, which are relevant for single- and double-Higgs production at current and future colliders.

Speaker: Alain Verduras Schaeidt (T (Phenomenology))

Theory_25_AVS.pdf

14:30 Renormalisation scheme dependence of the trilinear Higgs coupling in extended scalar sectors

The trilinear Higgs coupling $\lambda_{hhh}$ of the detected Higgs boson is a critical observable for understanding of the Higgs potential. With improving experimental bounds in the future, the theoretical predictions of this coupling for constraining BSM parameters become increasingly significant. Using the public code anyH3, this study investigates the numerical stability of different renormalization schemes for $\lambda_{hhh}$ at one-loop level in extended scalar sectors. By comparing predictions of the coupling for various schemes, this study develops algorithmic criteria for switching between renormalisation schemes depending on the parameter region of the BSM model. This approach ensures numerically stable and reliable predictions for the trilinear Higgs coupling.

Speaker: Marc Hannig (T (Phenomenology))

Renormalisation scheme dependence Desy Theory Workshop.pdf

14:45 Intelligent Scans in the NMSSM

The next-to-minimal supersymmetric extension of the Standard Model (NMSSM) belongs to the most prominent, best motivated and experimentally widely tested beyond-SM extensions. For a meaningful interpretation of the experimental results and in order to be able to pin down the model underlying nature from the theory side, precise predictions for observables and parameters are crucial. Moreover, in view of the SM-like nature of the Higgs boson all relevant experimental and theoretical constraints have to be considered to corner valid new physics models. Because of the non-minimal number of input parameters, an intelligent scan procedure of the parameter space is required in order to investigate the parameter space, taking into account all relevant constraints and then providing interesting benchmark points. In this talk, we present our recent progress on a program chain, starting with the code NMSSMCALC to calculate loop-corrected Higgs masses and decays and (newly incuded) supersymmetric particle decays. We then also discuss the setup for the performance of intelligent scans (e.g. via Markov chain Montecarlo or active learning) in the NMSSM with the tool BSMArt and other tools to check for experimental limits and constraints. Finally, we present some first results.

Speaker: Felix Egle (T (Phenomenology))

Presentation_FelixEgle.pdf

15:00 Hunting coloured scalars with machine learning

Several extensions of the Standard Model predict scalar states that are charged under QCD colour. Motivated by composite Higgs models, we study an electrically neutral colour octet and a colour sextet with charge 4/3. Both states couple to top quarks such that pair production leads to a four top quark signature. We train neural networks to separate these signal processes from their SM backgrounds and derive the discovery reach and expected exclusion limits at the HL-LHC. We also show that our networks can be used to efficiently identify which state is present.

Speaker: Manuel Kunkel (University of Würzburg)

kunkel_desy_2025.pdf

15:15 Probing $A\to ZH$ vs. $H \to ZA$ using top-quark spin correlations at the (HL-)LHC

We propose angular observables sensitive to top-quark spin correlations to distinguish between the pseudoscalar $A\to ZH$ and the scalar $H\to ZA$ signals (where $A$ and $H$ denote CP-odd and CP-even Higgs bosons, respectively) in $Zt\bar t$ final states at the HL-LHC. Current searches performed by ATLAS and CMS are insensitive to the CP nature of BSM scalar states in the case of identical production cross sections. In the context of the CP-conserving two-Higgs-doublet model, we demonstrate that, for a benchmark scenario with masses of 800 and 600 GeV, angular variables sensitive to top-quark spin correlations can differentiate between the two scenarios, even when the production rates are identical. These searches are of great interest in probing parameter space regions that predict a strong first-order electroweak phase transition.

Speaker: Francisco Manuel Arco Garcia (T (Phenomenology))

Arco-th-workshop.pdf

15:30 Electroweak spin-1 resonances in Composite Higgs models

Composite Higgs models offer an elegant solution to the hierarchy problem by assuming that the Higgs boson is not an elementary particle but a composite state. The Higgs emerges as a pseudo-Nambu-Goldstone boson due to spontaneous symmetry breaking within a new strongly interacting sector.
We focus on minimal realizations of such models with fermionic UV completions that preserve custodial symmetry and naturally include fermionic resonances acting as top partners. These models predict spin-1 resonances which carry electroweak quantum numbers.
We find that three such states mix significantly with the electroweak gauge bosons, allowing their single production in Drell-Yan-like processes at the LHC. We explore the rich LHC phenomenology of these states and find scenarios where their masses could be as low as 1.5 TeV.

Speaker: Jan Hadlik (University of Würzburg)

EWSpin1ResonancesCHM_DESY25.pdf

15:45 Testing Composite Higgs models with Vector Boson Scat- tering at LHC

In recent years, Vector Boson Scattering (VBS) has been extensively stu-
died to gain a deeper understanding of the fundamental interactions and the
gauge structure of the Standard Model (SM). Additionally, it serves as a po-
werful probe for new physics processes at multi-TeV energy scales, offering
a window into physics beyond the Standard Model.
Composite Higgs models instead provide a promising solution to the Natu-
ralness problem of the Higgs sector.
Our focus is on Composite Higgs models with a fermionic UV completion
that predict the existence of spin-1 resonances mixing with the W and Z
bosons. For some of these models, these electroweak spin-1 resonances can
be as light as 1.5 TeV consistent with all direct searches. We investigate in
which extent VBS con give further constraints for these models.

Speaker: Rosy Caliri (University of Würzburg)

Rosy_s_DESY_Template.pdf

16:00 Coffee break

16:30 BSM Higgs physics at the Photon collider

High-energy $\gamma\gamma$- and $e\gamma$-collisions offer a rich phenomenological programme, complementary to $e^+e^-$ collisions at a linear collider both in kinematic as well as physics reaches. In particular, $\gamma\gamma$ collisions offer a unique setting to investigate properties of the Higgs boson(s). High polarisation of the photon beams (produced via Compton back-scattering) can be achieved and adjusted by flipping the polarisation of the incident laser. Furthermore, prospects for di-Higgs production at a $\gamma\gamma$ collider are particularly promising, and could open the way to a direct measurement of the trilinear Higgs self-coupling, at lower centre-of-mass energies than at an $e^+e^-$ collider.
In this talk we will present new results about the di-Higgs production process at the $\gamma\gamma$ collider, comparing different running scenarios (with different types of incident laser). We will discuss the possibility of measuring the trilinear Higgs coupling, also making use in this context of photon polarisations to disentangle different contributions to di-Higgs production.

Speaker: Marten Berger (FTX)

Berger_DESYTHWorkshop2025.pdf

16:45 Dark Matter Aspects of the Composite Higgs Models

The nature of Dark Matter (DM) and the origin of small neutrino masses remain open questions in particle physics, motivating extensions of the Standard Model. In this talk, I explore Composite Higgs (CH) models that can simultaneously address both issues. As a concrete example, I will present a CH model based on the coset SU(6)/Sp(6), which naturally provides potential DM candidates as a composite pseudo-Nambu–Goldstone boson. I will discuss the phenomenological implications, focusing on explaining the DM relic density within this framework.

Speaker: Yu Chen (Universität Würzburg)

YChen_DESY.pdf

17:00 Inelastic Dark Matter at ProtoDUNE

Liquid argon Time Projection Chambers (LArTPCs) have proven to be powerful instruments for detecting weakly interacting particles predicted by many beyond the Standard Model (BSM) scenarios. Thanks to their location at CERN, the ProtoDUNE detectors can intercept a sizeable flux of such particles, produced when the 400 GeV protons from the Super Proton Synchrotron (SPS) impinge on a fixed target. In this talk, I will focus on the inelastic dark matter (iDM) model and search for its dark photon mediator in ProtoDUNE. I will outline the projected sensitivity reach for its mixing parameter, $\varepsilon$, and its mass, $m_{A'}$.

Speaker: Sara Bianco (T (Phenomenology))

DESYTheoryWorkshop2025_SaraBianco.pdf

17:15 Quirk SUEP

We propose searching for physics beyond the Standard Model in the low-transverse-momentum tracks accompanying hard-scatter events at the LHC. TeV-scale resonances connected to a dark QCD sector could be enhanced by selecting events with anomalies in the track distributions. As a benchmark, a quirk model with microscopic string lengths was developed, including a setup for event simulation. For this model, strategies are presented to enhance the sensitivity compared to inclusive resonance searches: a simple cut-based selection, a supervised search, and a model-agnostic weakly supervised anomaly search with the CATHODE method. Expected discovery potentials and exclusion limits are shown for 140 fb−1 of 13 TeV proton-proton collisions at the LHC. This work is documented in arXiv:2506.11192.

Speaker: Max Fuste Costa (ATLAS (ATLAS-Experiment))

Quirks SUEP.pdf

14:00 → 17:30 Parallel Sessions Thursday Pheno 2

14:00 TeV-scale scalar leptoquarks: towards a combined solution to the flavor anomalies and GUT shortcomings

It is common practice to explain deviations between data and Standard-Model predictions by postulating new particles at the TeV scale ad-hoc. This approach becomes much more convincing, if one successfully embeds the postulated particles into a UV completion which addresses other conceptual or phenomenological shortcomings of the SM. We present a study of an SO(10) grand unified theory which contains scalar leptoquark fields employed to explain the flavor anomalies in $b\rightarrow s$ and $b\rightarrow c$ decays. We find that the additional degrees of freedom improve the renormalization group evolution of the SM parameters and may explain some of the observed fermion masses.

Speaker: Xiyuan Gao (KIT, Karlsruhe, TTP)

Gao-09.25.2025.pdf

14:15 Flavored Circular Collider: cornering New Physics at FCC-ee via flavor-changing processes

We illustrate the potential of a future high-intensity $e^+e^-$ collider operating at the $Z$ pole to probe extensions of the Standard Model through precise measurements of flavor-changing processes, both within the framework of effective field theories and in simplified models motivated by current BB-physics anomalies. Our focus is on selected flavor-physics projections at FCC-ee and on a theoretically well-motivated scenario involving TeV-scale new physics predominantly coupled to third-generation fields. In particular, we demonstrate the crucial role of the interplay among various flavor observables, as well as between flavor and electroweak precision measurements, in constraining the New Physics parameter space.

Speaker: Marko Pesut (University of Zürich)

Flavour&EW@FCC_DESY.pdf

14:30 The Higgs self coupling in the presence of $e^+e^--t\bar{t}$ -interactions

The Higgs self coupling is one of the last not precisely measured couplings in the SM with a current precision of $\mathcal{O}(100\%)$. Within the SMEFT, the BSM contribution to the trilinear self coupling of the Higgs is the operator $\mathcal{O}_H$, which enters at NLO in the $e^+e^- \to ZH$ cross section, providing an interesting probe for the self-coupling at future lepton colliders. However, at NLO in SMEFT also $eett$-interactions enter, potentially spoiling the sensitivity to the Higgs trilinear by entering at the same order. We will show how the presence of these operators, which are well motivated by different BSM scenarios, would instead not spoil the measurement of the self-coupling, by exploiting the synergies with additional observables, like EWPO and $ee\to bb$ production. We will analyse the problem both from a global SMEFT fit perspective and from a simplified model approach featuring heavy extensions of the SM.

Speaker: Lucine Tabatt (T (Phenomenology))

TabattDESYTW.pdf

14:45 Probing Flavorful EFTs via VH and WV production at the LHC

Since the discovery of the Higgs boson, no clear footprints of New Physics (NP) have been observed at the LHC. This absence suggests a separation between the scale of NP and the electroweak scale. In this scenario, Effective Field Theories (EFTs) provide a model-independent framework to analyze LHC data and search for indirect signs of beyond-the-Standard-Model effects. In particular, diboson production (WV) and Higgs production in association with a gauge boson (VH) are sensitive to NP, especially in the high-energy tails of kinematic distributions. These energy-enhancement effects enable the extraction of constraints that can be competitive with those from electroweak precision observables, such as those measured at LEP. In this talk, I will discuss how WV and VH processes can probe the Wilson coefficients of Higgs current operators in the Standard Model EFT—specifically, operators that modify the couplings between gauge bosons and fermions—without imposing flavor assumptions. I will also show how these results can be complementary to those from electroweak precision observables and how the High-Luminosity LHC can help clarify current low-energy flavor anomalies.

Speaker: Matheus Martines de Azevedo da Silva (Universidade de São Paulo)

ProbingFlavorfulEFTs_pp_VW_LHC-DESY.pdf

15:00 Threshold effects on the massless neutrino in the canonical seesaw mechanism

In this talk, we revisit the one-loop renormalization group equations (RGEs) among nondegenerate seesaw scales, i.e., threshold effects in the canonical seesaw mechanism, which have been obtained for more than two decades. Different from the previous work only focusing on the Weinberg operator, we derive the complete one-loop RGEs of all three dimension-five operators in the Standard Model effective field theory with right-handed neutrinos (νSMEFT) and apply them to threshold effects in the canonical seesaw mechanism. We find some contributions from the Weinberg operator to its Wilson coefficient, the neutrino Yukawa coupling matrix, and the Higgs quartic coupling absent in the previous calculations. Based on the updated one-loop RGEs, we derive the RGE of the effective neutrino mass matrix’s determinant without any approximation. Then, for the first time, we provide a strict proof that the one-loop RG running effects among non-degenerate seesaw scales can not generate a non-zero mass for the initial massless neutrino in the minimal type-I seesaw mechanism or in the canonical one with a rank-degenerate neutrino Yukawa coupling matrix. One has to include two- or higher-loop corrections to achieve a non-zero mass for the massless neutrino

Speaker: Di Zhang (Technical University of Munich)

Di_Zhang_25.09.2025@DESY.pdf

15:15 Disentangling left and right-handed neutrino effects in $ B \to K^{(*)} \nu \nu $

The first observation of $\mathcal{B}\left(B^+\rightarrow K^+\nu\nu\right)$ by the Belle II experiment lies almost $3\sigma$ away from the Standard Model expectation. In this work we study this result in the SMEFT, extended by a light right-handed neutrino. We explore the correlations between the measured decay rate and other observables, such as $\mathcal{B}\left(B\rightarrow K^*\nu\nu\right)$ and $F_L\left(B\rightarrow K^*\nu\nu\right)$, showing that they could disentangle among scenarios involving left-handed neutrinos and those with the right-handed ones. Furthermore, we find that the high-$p_T$ tails of Drell-Yan processes studied at LHC provide important constraints that help us exclude some of the scenarios consistent with the Belle II result.

Speaker: Luighi Leal (University of Sao Paulo)

Luighi_Leal_DESY_Workshop_2025.pdf

15:30 Heavy Meson Lifetimes using Gradient Flow

Lifetimes of mesons containing a heavy quark can be described by an operator product expansion involving four-quark operators. To determine these lifetimes, both perturbative Wilson coefficients as well as non-perturbative hadronic matrix elements are needed. The gradient-flow formalism provides a way for calculating the latter in lattice gauge theory. Suitable perturbative matching coefficients allows one to combine them with the corresponding Wilson coefficients. We report on first results of this method, with a focus on the perturbative evaluation of the matching coefficients to next-to-next-to-leading order in perturbation theory.

Speaker: Jonas Kohnen

talk.pdf

15:45 Three-loop QCD corrections to heavy-to-light form factors and applications to inclusive $B$ decays

In this talk, we discuss the computation of form factors for decays of heavy into light quarks at third order in QCD for various currents. We describe the different steps of the calculation and use the results to compute the hard matching coefficients in Soft-Collinear Effective Theory for all currents. Further, we extract the hard function in $\bar B \to X_s \gamma$ to three loops and study the impact of three-loop QCD corrections on partial decay rates in charged-current semi-leptonic $\bar B \to X_u l \bar \nu$ decays.

Speaker: Jakob Müller

desy_th_jmueller.pdf

16:00 Coffee break

16:30 Multi-parton contributions to $\bar B \to X_s \gamma$ at NLO

The calculation of the branching ratio for the inclusive decay $\bar B \to X_s \gamma$ has been an active field of research for multiple decades, yielding results that work very well as a
standard candle of the Standard Model of Particle Physics (SM). In this work, we calculate the remaining pieces for the branching ratio of the four-body decay of a b quark into an s quark, a photon $\gamma$ and two additional quarks $q\bar{q}$ at NLO in the strong coupling $\alpha_s$. This calculation involves the one-loop process $b \rightarrow s \gamma q \bar q$, with a virtual gluon, as well as the tree-level contribution to $b \rightarrow s \gamma q \bar q g$.

Speaker: Kevin Marc Brune

Desy_Brune.pdf

16:45 A weak effective theory approach to probing ALPs in B-decays

Rare decays like B→Ka offer a sensitive window to search for axion-like particles (ALPs), especially for heavier ALPs with masses in the range of MeV to a few GeV. We present a detailed study of these decays within the framework of weak effective theory. We show that to consistently include ALPs in this framework, one must extend the usual set of effective operators by introducing new ones. We focus on the case where ALP couplings to SM fermions are flavor-diagonal, so that flavor-changing effects are induced through effective weak interactions. We explore how this setup affects bounds on ALP couplings and compare it to scenarios where ALPs have explicit flavor-changing interactions: first in a model-independent way, and then by studying how the picture changes when the low-energy couplings are generated from UV models with flavor-universal ALP couplings at the high energy scale.

Speaker: Upalaparna Banerjee (Johannes Gutenberg University of Mainz)

DESY_workshop_UB.pdf

17:00 Axion production and detection using NMR-type experiments

Axions that couple to nuclear spins via the axial nuclear moment interaction can be both produced and detected using NMR techniques. The gradient of the radiated axion field is set by the size of the spin-polarized source, which can greatly exceed that of ambient axion dark matter. This sourced axion field can be resonantly detected using NMR and measured with sensitive magnetometers. In this talk, I will present a calculation of the experimental sensitivity. As I will show, a pair of centimeter-scale NMR devices operating over a one-day integration time can already surpass existing astrophysical bounds on the axion-nucleon coupling, including those from star cooling. This setup is capable of probing a wide range of axion masses, up to values comparable to the inverse size of the spin source.

Speaker: Fengwei Yang (University of Florida & University of Notre Dame)

axion production and detection - DESY.pdf

14:00 → 18:00 Parallel Sessions Thursday String

14:00 Epsilon-factorising multi-scale Feynman integrals with Calabi-Yau geometry

We will discuss the epsilon-factorisation of multi-scale Feynman integrals with an underlying Calabi-Yau geometry.
We have computed for the first time a canonical form for the three-loop banana integral with two unequal masses and for a four-loop banana integral with two unequal masses.
We discuss the transcendental functions needed to epsilon-factorise the differential equation.
These functions turn out to be periods of Calabi-Yau manifolds.

Speaker: Yoann Sohnle (Uppsala University)

talk_desy.pdf

14:15 Determining masses of hadronic bound states using a holographic ansatz

Holography has been found to be an exceptional tool in particle physics. In this talk I will introduce a holographic bottom-up model based on $AdS_5/CFT_4$ which we use to describe a QCD-like theory. In this model one can calculate masses of scalar and vector mesons as well as baryons. I also introduce a way of including an additional global symmetry on the field theory side. This can be used to include flavor symmetry in such a model. Breaking this symmetry by giving different masses to the quarks gives predictions for the lightest QCD baryons which match the measured results surprisingly well.

Speaker: Konrad Becker

Determining masses of hadronic bound states using a holographic ansatz, Konrad Becker.pdf

14:30 Superconformal Invariants for 5-point correlators in N=4 SYM

We study five-point correlators of 20' half-BPS operators in $\mathcal{N}=4$ super Yang-Mills theory at one and two loops. For this we reboot the superconformal bootstrap programme for higher points perturbative integrands and formulate the problem in analytic superspace to make the full power of superconformal symmetry accessible from the outset. We then systematically derive the full list of next-to-maximally-nilpotent tensor superconformal invariants, giving explicit expressions for their projection to the five point integrand. These must be contracted by appropriate tensor functions of spacetime $x_i$ (as well as the internal space $y_i$ at higher charges) of the right weight, which we also systematically derive. In this way we obtain a complete ansatz for the correlator as a linear combination of independent terms, all transforming correctly as the correlator under the full superconformal group. We then apply this to the five-point one- and two-loop stress-tensor multiplet correlator. We impose $S_{5+\ell}$ crossing symmetry, together with a simple constraint arising from the OPE and obtain a unique result for both, thus completely fixing (up to an overall numerical factor) both correlators. As explicit new results we obtain full explicit expressions (both parity even and odd parts) of the five point one- and two-loop correlators.

Speaker: Tabea Siebrecht (T (Stringtheory))

invariants_presentation.pdf

14:45 Self-organized criticality in a relativistic Yukawa theory with Luttinger fermions

We study a relativistic Yukawa model featuring a dynamical scalar field coupled to Luttinger fermions. Using the functional renormalization group alongside large-$N_\text{f}$​ and perturbative techniques, we find an infrared-attractive partial fixed point where all interactions become irrelevant, and the scalar mass parameter remains marginal, featuring a slow, logarithmic flow towards spontaneous symmetry breaking. Crucially, the model exhibits mass gap generation for both fermions and scalars, independent of microscopic details. Most notably, a large scale separation between the IR and UV scales arises naturally for generic initial conditions, without any fine-tuning. We interpret these features as a relativistic realization of self-organized criticality, leading to universal long-range behavior.

Speaker: Marta Picciau (TPI Uni Jena)

Picciau.pdf

15:00 Associators for string amplitudes and number theory

The Drinfeld and Deligne associators have a close connection to string amplitudes: In this talk I will present techniques to generate open- and closed-string amplitudes from these associators in flat space as well as in AdS backgrounds. Furthermore I will show their relations to polylogarithms and multiple zeta values and extensions to loop amplitudes.

based on:
- arXiv:2412.17579 with J. Broedel and F. Zerbini
- arXiv:2505.23385
- work in progress with J. Broedel

Speaker: Konstantin Baune (ETH Zürich)

Baune-StringRecursions.pdf

15:15 Non-perturbative results in conformal field theories at finite temperature

Finite-temperature systems have always played a central role in physics. In recent years, the study of conformal field theories in a thermal state has gained momentum, with applications ranging from condensed matter to quantum gravity and black holes. In this talk, I will explain how the structures of conformal field theories allow us to set up a thermal bootstrap problem and gain access to non-perturbative observables at finite temperature. In particular, I will focus on the critical 3D Ising model and on holographic theories, and show how one-point and two-point functions can be bootstrapped, producing both results in accordance with previous estimates and new ones.

Speaker: Enrico Marchetto (T (Stringtheory))

DESY Theory Workshop 25-09-2025.pdf

15:30 Toward the mixed correlator bootstrap of 6d (2,0) theories

We outline progress toward the superconformal bootstrap of multiple mixed correlators in the 6d (2,0) theories, generalizing the initial study in [1507.05637]. The first step was achieved in [2506.08094], where we extracted an infinite set of exact, protected CFT data from the (2,0) theories' cohomological reduction to W-algebras. To bootstrap full (untwisted and unprotected) 4-pt. functions, we are generalizing the reduced superblock formalism to higher-charged correlators and deriving 1/4 BPS chiral ring relations among CFT data outside the W-algebra sector in certain low-rank (2,0) theories. These developments will, respectively, streamline and guide an eventual numerical bootstrap study of these systems of mixed 6d (2,0) correlators.

Speaker: Mitchell Woolley (Queen Mary University of London)

W_algebra_bootstrap_of_6d_2,0_theories.pdf

15:45 Searching for inflationary regimes in penumbral regions of the moduli space

One of the most compelling questions of string phenomenology is how to find viable inflationary models stemming from string theory. While asymptotic regions of the moduli space have been extensively explored - with limited success - little is known about inflationary dynamics in transitional, or 'penumbral', regions. In this talk, I will focus on the complex structure moduli space of Type IIB string theory compactified over Calabi-Yau three-folds. I will present evidence for flattened scalar potential valleys, which could deliver inflationary trajectories, in penumbral regions of the moduli space, and I will illustrate how to obtain families of effective theories hosting such valleys by using machine learning techniques.

Speaker: Stefano Lanza (UNI/TH (Uni Hamburg, Institut fuer Theoretische Physik))

Lanza_Stefano_DESY_Theory_Workshop.pdf

16:00 Coffee break

16:30 The Four-Point Non-Planar Integrand in N=4 Super Yang–Mills Theory at Five Loops

We compute the complete non-planar integrand for the correlation function of four lightest scalar operators in $\mathcal{N} = 4$ super Yang–Mills theory at five-loop order. This is equivalent to the super-correlator of nine lightest half-BPS multiplets in the self-dual theory. Starting with an ansatz of $f$-graphs, we impose constraints from light-cone limits, and fix the remaining freedom using the twistor reformulation of $\mathcal{N} = 4$ SYM. We implement a fast algorithm working on graphics processing units (GPUs) to substantially accelerate the contractions of the involved Grassmann numbers, that are introduced by the twistor rules.

Speaker: Albert Bekov (T (Stringtheory))

Talk_DESYWorkshop2025_Bekov.pdf

16:45 SymTFT for spacetime symmetries

Symmetry Topological Field Theories (SymTFTs) are topological field theories that encode the symmetry structure of global symmetries in terms of a theory in one higher dimension. While SymTFTs for internal (global) symmetries have been highly successful in characterizing symmetry aspects in the last few years, a corresponding framework for spacetime symmetries remains unexplored. We propose an extension of the SymTFT framework to include spacetime symmetries. In particular we propose a SymTFT for the conformal symmetry in various spacetime dimensions. We demonstrate that certain BF-type theories—closely related to topological gravity theories—possess the correct topological operator content and boundary conditions to realize the conformal algebra of conformal field theories living on boundaries. As an application, we show how effective theories with spontaneously broken conformal symmetry can be derived from the SymTFT, and we elucidate how conformal anomalies are reproduced in the presence of even-dimensional boundaries.

Speaker: Nicola Andrea Dondi (ICTP - Trieste)

DESY_2025.pdf

17:00 From Critical Points to Syzygies for Feynman Integrals

We investigate a novel theoretical structure underlying the computation of integration-by-parts (IBP) relations in perturbative quantum field theory via syzygy-based methods. Building on insights from intersection theory, we analyze the large-ϵ limit of dimen-sional regularization on the maximal cut, showing that total derivatives vanish on the critical locus of the logarithm of the Baikov polynomial-the locus known to govern the number of master integrals. We introduce critical syzygies as a distinguished subset of syzygies that captures this behavior. We show that, when the critical locus is isolated, critical syzygies generate a complete set of total derivatives in the large-ϵ limit. We study their structure analytically at one loop and develop a numerical algorithm for their construction at two loops. Our results demonstrate that critical syzygies provide a complete basis of total derivatives in cutting-edge two-loop examples, offering a geometric refinement of IBP reduction techniques.

Speaker: Qian Song (Ghent University)

DesyTheoryWorkshop-2.pdf

17:15 On extended moduli spaces of 4d N=1 theories

We study the possible non-perturbative transitions in the extended moduli spaces of 4d $\cN=1$ theories of quantum gravity arising from string theory compactifications. For these theories, the perturbative moduli spaces are well understood. We argue, however, that this perturbative perspective is incomplete since at the non-perturbative level the moduli space gets extended if the theory contains subsectors featuring enhanced supersymmetry. This moduli space extension is well known in 6d $\cN=(1,0)$ theories arising from string theory. Here, we investigate the 4d $\cN=1$ cousins of these non-perturbative, moduli space-augmenting transitions. The main focus lies on supersymmetry enhancements in the K\"ahler sector of F-theory compactifications signaled by a curve not intersected by 7-planes. In these setups identifying the additional degrees of freedom responsible for the enhancement of the supersymmetry, we demonstrate how the moduli space is augmented at the non-perturbative level.

Speaker: Gonzalo Fernandez Casas (IFT)

desy workshop Gonzalo.pdf

17:30 Growth and Dynamics of Cosmic Superstrings with Field-Dependent Tension

A novel mechanism to produce a cosmic network of fundamental superstrings based on a time-varying string tension has been recently proposed. It has been found that fundamental (super)strings can grow in a kinating background driven by the rolling of the volume modulus of Type IIB string compactifications towards the minimum of its potential. In this talk, I will generalise this analysis using dynamical systems techniques. First, I will analyse the cosmological growth of strings with a field-dependent tension in a spatially flat Universe filled with a perfect fluid, finding the fixed points of the phase space of this system. This machinery is then applied to both fundamental superstrings and effective strings obtained from wrapping $p$-branes on $(p-1)$-cycles. I will show how cosmological growth can be achieved in both cases not only in kinating backgrounds, but also in scaling fixed points. I will finally discuss how the strings behave once the rolling field reaches its minimum and starts oscillating.

Speaker: Luca Brunelli (University of Bologna)

Brunelli_DESY.pdf

17:45 Quantization of the rational spin Ruijsenaars–Schneider model and the affine Yangian

I will present a method of quantizing the rational spin
Ruijsenaars–Schneider integrable model of $N$ particles and $\ell$ spin
states via quantum Hamiltonian reduction, placing it within the
framework of quantized quiver varieties. Starting from the quantum
cotangent bundle of $GL_N$, we derive a non-commutative algebra that
encodes the quantum observables of the RS model with internal spin
degrees of freedom. This algebra naturally emerges as a quantization of
a quiver variety associated to the framed Jordan quiver. I will
highlight the appearance of both loop algebra and Yangian symmetries in
this setup, which govern integrability and enable a computation of the
energy spectrum.

Speaker: Lukas Hardi

15_min_spin_RS_presentation.pdf

Hardi.pdf

Friday 26 September

09:00 → 11:00 Plenary Session Friday I

09:00 Neutrino physics overview

Speaker: Julia Gehrlein

Gehrlein_neutrinos.pdf

09:40 Towards High Precision at the (HL-)LHC

Speaker: Stephen Jones

fedecc2c-3b6a-4a17-9bdb-b3494ac2200a.pdf

10:20 Recent progress in top-quark physics

Speaker: Maria Vittoria Garzelli

top.pdf

11:00 → 11:30 Coffee break

11:30 → 12:50 Plenary Session Friday II

11:30 Deep structure of proton

Speaker: Oleksandr Zenaiev

Zenaiev-DESYTH.pdf

12:10 Theory challenges at future e+e- colliders

Speaker: Matthias Steinhauser

steinhauser_desy.pdf

12:50 → 12:55 Closing