Welcome and Icebreakers

Generalized symmetries and non-invertible naturalness (30'+15')

• Seth Koren (Notre Dame U.)

Skyrme-Dilaton

• Roman Zwicky (U. Edinburgh)

I will motivate that the sigma meson could be a dilaton through gravitational form factors, which serve as a test of the IR-conformal ward identities in the broken phase. Then review the Skyrme model and introduce the sigma as dilaton to the model. It will be tested against static nucleon properties and shown to improve predictions considerably.

One instanton, many consequences: Axion potentials and proton decay, beyond the Standard Model (30'+15')

• Pablo Sesma (IFAE Barcelona)

Daisy Resummation Beyond Leading Order (30'+15')

• Martin Münzenberg (JGU Mainz)

Metastable defects and gravitational waves (45'+15')

• Alberto Mariotti (Vrije Universiteit Brussel)

I will introduce basics aspects of cosmic defects, how they arise in cosmological phase transitions, and their implications for cosmology and gravitational waves. I will then revisit the case of metastable defects, both in axion models and in theories with symmetry-breaking patterns analogous to the electroweak sector of the Standard Model. Next, I will focus on metastable strings arising in a concrete dark sector model, which have recently been considered as candidates for explaining the gravitational-wave background observed by pulsar timing arrays (PTA). I will discuss how they can decay quantum mechanically, and I will then present an analysis of their classical stability, where I will show that classical instabilities can affect the parameter space relevant for explaining the PTA signal. I will conclude by outlining future directions in the study of metastable defects.

Renormalisable four-fermion interactions in four dimensions (30'+15')

• Charlie Cresswell-Hogg

Four-fermion interactions are important in many areas of particle physics, from effective descriptions of weak interactions and QCD to parametrisations of new physics in frameworks such as SMEFT. In this talk I demonstrate that four-fermion interactions may develop strongly coupled UV fixed points in four dimensional QFTs, becoming non-perturbatively renormalisable, and UV completing themselves from the bottom up. The idea will be illustrated in a purely fermionic model of the Gross-Neveu type using the toolbox of the large-N expansion.

Non-adiabatic sphaleron biasing and Baryogenesis (30'+15')

• Miguel Vanvlasselaer (U. Barcelona)

Renormalizing the Nonrenormalizable in Perturbation Theory (45'+15')

• Litim Daniel

Effective methods for bubble nucleation in cosmological phase transitions (30'+15')

• Maciej Kierkla

I will present an overview of the calculation of the thermal bubble nucleation rate in the context of cosmological phase transitions (PT). Focusing on the case of “SU(2)+Higgs” like theories, I will illustrate the calculation of the nucleation rate in the framework of high-temperature dimensional reduction. I will present next-to-leading order results and discuss the limitations of employing derivative expansion in the perturbation theory. Finally, I will discuss the most relevant theoretical uncertainties that affect predictions for gravitational-wave (GW) signals from first-order PTs in the early Universe. Furthermore, I will discuss their impact on the possible reconstruction of the underlying BSM physics from measured GW signals.

Dynamics of nucleation in first-order phase transitions (30'+15')

• Andrey Shkerin (Perimeter Institute)

I will discuss dynamical effects during bubble nucleation in thermal first-order phase transitions. These effects arise due to lack of local thermal equilibrium and affect the parameters of the transition including the nucleation rate. I will present a general method of calculating the dynamical nucleation rate. I will also present results from real-time classical lattice simulations showing the importance of the non-perturbative contribution to the dynamical prefactor. These results can be important in many areas, from cosmological phase transitions to studies of false vacuum decay in quantum simulators.

Thermal nucleation in perturbation theory (30'+15')

• Joonas Hirvonen (Nottingham U.)

Cosmological first-order phase transitions may have generated a gravitational wave background detectable by LISA, offering a unique window into physics beyond the Standard Model. A crucial step in predicting this background is the reliable computation of bubble nucleation rates. In this talk, we overview the current state of perturbative calculations based on effective field theories and Boltzmann equations. We also introduce a recent approach to nucleation based on Wigner functions, which provides a solid quantum-mechanical foundation for these existing frameworks. In addition, it allows for including further quantum effects to the rate, thereby extending the validity to lower temperatures, and enabling higher precision. We conclude by discussing remaining open questions in perturbative approaches, highlighting directions for future developments.

Some thoughts on field redefinitions and/or low energy potentials (45'+15')

• Joerg Jaeckel (Heidelberg U.)

Higher Charge Monopoles and GUT Physics (30'+15')

• Daniel Brennan (Birmingham U.)

Towards the exotic infrared phases of chiral gauge theories (30'+15')

• Alvaro Pastor Gutierrez

The infrared structure of gauge theories with chiral fermions remains largely unexplored. In this talk I will discuss the Bars-Yankielowicz class using the functional renormalisation group, building on recent developments in gauge-fermion systems that provide clear criteria for confinement and dynamical symmetry breaking. I will show how two distinct phases arise: one exhibiting both confinement and symmetry breaking at small numbers of colours, and another characterised by confinement without symmetry breaking in the large-colour limit. The latter realises a novel regime, opening the possibility of exotic spectra and phenomena that can now be studied within a systematic framework.

Supercooling and Conformality in confining transitions (30'+15')

• Gaurang Ramakant Kane

Understanding the dynamics of first-order thermal deconfinement–confinement transitions in strongly coupled gauge theories is an open problem that has been studied from various perspectives, including supersymmetry, holography, and explicit lattice computations—each approach revealing a different aspect of the transition. In addition to their theoretical interest, such transitions are also phenomenologically relevant, as they may leave behind potentially detectable relics, such as gravitational waves and dark matter abundance. Motivated by these phenomenological implications, in this talk, I will discuss progress in understanding one aspect of these transitions, namely, supercooling. Using explicit examples and a general holographic argument, we will see that the maximum possible supercooling in such theories is closely related to the degree of conformality of the theory near the critical temperature.

Week 2 Icebreakers

Self Consistent Thermal Resummation: A Case Study of the Phase Transition in 2HDM

• Pedro Bittar (Perimeter Institute)

Dynamical evolution of the pressure on the bubble wall (30'+15')

• Benoit Laurent (Perimeter Institute)

First-order cosmological phase transitions proceed through the nucleation and growth of bubbles of the new phase, and can be a leading source of gravitational waves, baryogenesis, and dark matter in the early Universe. A central question is what happens to a bubble immediately after it nucleates: does the wall settle into a slow, subsonic regime, or does it accelerate to ultra-relativistic velocities? This outcome is controlled by hydrodynamic obstruction, whereby heating of the surrounding plasma counteracts the vacuum pressure that drives the wall. In this talk I focus on the early evolution of the bubble right after nucleation, a stage usually left out of wall-velocity calculations. Standard analyses assume that the fluid around the wall has already relaxed to a steady-state profile, but this assumption can break down precisely while the wall is still accelerating. Working in local thermal equilibrium (LTE) and combining analytical approximations with numerical hydrodynamic simulations, we find that the heating wave often takes longer to form than the wall takes to accelerate, so steady-state predictions fail near the speed of sound. From this we derive a revised criterion for the maximal driving pressure, separating deflagration and hybrid solutions from detonations and runaway walls. Validated against simulations, the criterion shows that hydrodynamic obstruction is less restrictive than steady-state LTE predictions suggest.

Chiral Gauge Theory on a Computer (45'+15')

• Markus Luty (UC Davis)

Extracting zero-damped modes using exact WKB (30'+15')

• Nils Wagner (TU Munich)

Zero-damped quasinormal modes are a characteristic feature of near-extremal black holes and are expected to play an important role in their late-time ringdown. In this talk, I will give a pedagogical introduction to the exact WKB method and show how it can be used to study the zero-damped spectrum of near-extremal Reissner--Nordström black holes, highlighting recent developments that make this analysis possible.

Another Brick in the Wall: Domain Wall Networks Beyond Z₂ (30'+15')

• Dhruv Pasari (Durham University)

Domain walls beyond the textbook Z₂ kink have been studied analytically and through effective models, but seldom simulated directly on the lattice. We close that gap, evolving Z₃ and Z₄ wall networks with CosmoLattice. These networks are qualitatively richer than Z₂: walls come in distinct species, meet along junctions, and can transmute into one another rather than simply annihilating. To capture this we develop a wall-counting algorithm for multi-component fields that separates each species, and use it to measure the late-time scaling area of each. In Z₄ the simulations directly exhibit a stability transition, where "opposite" walls split into pairs of "adjacent" walls, confirming our analytic prediction. Finally, we extend the velocity-dependent one-scale model from Z₂ to general Zₙ, encoding the reduced annihilation efficiency and junction friction so that the measured scaling plateaus feed directly into the network dynamics, and ultimately the gravitational-wave signal.

Bounding a dark sector ChiPT Lagrangian with unitarity (45'+15')

• Mia West (KIT)

UV/IR Mixing Through the Lens of Tensor Networks (30'+15')

• Steven Abel

Gravitational waves from critical dynamics (30'+15')

• Oliver Gould (Nottingham U.)

Thermal partition function from the S-matrix reloaded (45'+15')

• Joan Elias Miro (ICTP Trieste)

Over the past decade, S-matrix-based methods have undergone a remarkable resurgence as elegant and powerful tools for extracting physical information without relying on an underlying Lagrangian formulation. A central question is: given the exact S-matrix of a quantum field theory, what can we learn about its thermodynamic properties? In this talk, I will review the Dashen–Ma–Bernstein formalism, which relates thermodynamics directly to scattering amplitudes. I will illustrate it with the perturbative QCD equation of state and with the effective theory of long confining flux tubes, including non-universal corrections and comparisons with Thermodynamic Bethe Ansatz results. More broadly, these methods offer a way to extract thermodynamic observables directly from on-shell data, with potential applications to EFTs constrained by modern bootstrap and positivity techniques.

Real-time tunneling calculations in the steadyon picture (30'+15')

• Thomas Steingasser (IFT/CSIC, UAM)

Quantum tunnelling is conventionally formulated through Euclidean instantons, obscuring the role of physical time and complicating non-vacuum initial states. I will review the steadyon picture, in which infinitesimally regulated real-time path integrals are controlled by complex saddles whose projections recover familiar instantons. I will summarize its applications to finite-temperature decay, resonance states and states carrying conserved Noether charge, highlighting an emerging unified description of tunnelling beyond the false vacuum.

Excited-Vacuum Decay from Large-Order Perturbation Theory (30'+15')

• Yan Luo (DESY and USTC, Hefei)

Non-perturbative QFT on the twisted four-torus (45'+15')

• Mohamed Anber (Durham)

I will review the old 't Hooft construction of fractional instantons on the twisted four-torus and its relation to the modern language of 1-form symmetry. Then, I will describe how this setup enables us to perform nonperturbative calculations in QFT. In particular, I will discuss how to compute the gaugino condensates in supersymmetric theories on the four-torus.

Nonlocal Effective Field Theory Approach to Thermal Photon Condensation in a Strongly Magnetized Vacuum (30'+15')

• Selym Villalba-Chavez (HHU Düsseldorf)

Closing wods

• Felix Yu (JGU Mainz)