Thermal field theory and gravitational waves group meeting

Wednesday 28 Jan 2026, 10:00 → 13:30 Europe/Zurich

Science I, 222 (Ecole de Physique -- Université de Genève)

Alberto Roper Pol (University of Geneva), Philipp Schicho (University of Geneva)

10:00 → 12:00 Group Meeting

10:00 Limits of EFTs at finite temperature for strong phase transitions

Phase transitions are violent and interesting phenomena that could have occurred in the early universe. Possible techniques to study these phenomena can be used in the presence of a hierarchy of scales, leading to the construction of finite temperature Effective Field Theories by integrating out heavier scales. These EFTs are reliable when the dynamics are mainly encoded in the most relevant operators. I will discuss the limits of such EFTs, showing how higher-dimensional operators affect the prediction of stronger transitions, including those detectable by LISA. These considerations impact the applicability of effective theory techniques, including their use in lattice studies.

Speaker: Fabio Bernardo (Universitè de Genève)

10:30 Improving bubble wall velocity predictions in electroweak phase transitions

I study bubble wall velocities in first-order electroweak phase transitions using loop-corrected equations of motion for the Higgs field with plasma induced friction effects. These corrections affect the friction experienced by the bubble wall and play an important role in determining its steady state velocity, which is relevant for gravitational wave signals and probes of physics beyond the Standard Model.

Speaker: Salma Kämpf

11:00 Acoustic fluid perturbations in first-order phase transitions

First-Order Phase Transitions in the early Universe can source a Stochastic Gravitational Wave Background. If they occur at the electroweak scale, the resulting Gravitational Wave spectrum can peak in the LISA sensitivity band. Many processes in a First-Order Phase Transition can contribute to the resulting Gravitational Wave spectrum. The expanding scalar broken-phase bubbles can produce longitudinal perturbations in the primordial plasma which lead, after bubble collisions, to the development of sound waves. Moreover, due to the production of shocks, both across and after collisions, vorticity can be generated in the fluid, which, in the presence of magnetic fields, due to the high conductivity of the plasma, can lead to magnetohydrodynamic turbulence. A full understanding of the interplay between these processes is a challenging problem which requires both lattice simulations and analytical efforts. In this talk I will focus on the contribution from sound waves showing, in particular, the fundamental steps required to understand the properties of the Gravitational Wave spectrum starting from the fluid perturbations generated in the bubble expansion phase. The main result is an analytical prediction for the dependence on the phase transition parameters of the peak frequency scales in the Gravitational Wave spectrum.

Speaker: Antonino Midiri

11:30 The Heat-Kernel method and the effective theory of hot QCD

During this talk, I will show how one can use the Heat-Kernel method (also known as proper-time method) to compute the one-loop matching of the dimension-6 operators basis of the dimensional reduced effective theory of hot QCD (EQCD).

Speaker: Romain Guillermo Reinle

12:00 → 13:00 Lunch