VAST 2026: From Vacuum Stability to Gravitational Waves

Session

Formal Aspects Of Phase Transitions

Oct 22, 2026, 11:40 AM

Real Jardín Botánico, CSIC.

12. Dynamical evolution of the pressure on the bubble wall

Miguel Etienne A Vanvlasselaer (ICCUB)

10/22/26, 11:40 AM

First-order phase transitions in the early Universe are pivotal for gravitational wave production, baryogenesis, and dark matter generation. A central question is whether bubble walls reach a subjouguet or ultra-relativistic velocity - a distinction governed by hydrodynamic obstruction, where plasma heating counteracts the vacuum pressure driving the wall. Traditional analyses assume...

32. Convergence of bubble nucleation rates

Anna Kormu (University of Helsinki)

10/22/26, 12:00 PM

Nucleation rate computations are of broad importance in many aspects of physics, especially in the accurate estimation of the phase transition (PT) parameters that enter the gravitational wave (GW) power spectrum. The nucleation rate and PT parameters rely on perturbative estimates. Therefore, they are dependent on the details of the semiclassical picture and different orders of perturbative...

5. Toward a real-time theory of vacuum decay

Alex Jenkins (University of Cambridge)

10/22/26, 12:20 PM

False vacuum decay plays a pivotal role in the physics of the early Universe. However, we lack a satisfying theoretical understanding of this process, with existing approaches working only in imaginary (Euclidean) time, and relying on untested assumptions and approximations. In this talk, I will introduce two complementary approaches toward a real-time theory of vacuum decay: semiclassical...

4. An ode to instantons

Dr Oliver Janssen (EPFL)

10/22/26, 12:40 PM

We review a method to compute semiclassical time evolution in quantum mechanics via the path integral, illustrating how it works in paradigmatic examples. This includes the decay of general, excited metastable states from a false vacuum, generalizing a method due to Coleman for the would-be ground state. We then apply the method to compute the time-dependent decay rate of a particle that is...

23. On the validity of finite-temperature EFTs

Fabio Bernardo (Université de Genève)

10/22/26, 5:00 PM

Phase transitions are violent and fascinating phenomena that may have occurred in the early Universe. When a hierarchy of scales is present, they can be studied using finite-temperature Effective Field Theories, obtained by integrating out the heavier degrees of freedom. Such EFTs provide a reliable description as long as the dynamics are dominated by the most relevant operators. In this talk,...

30. A consistent EFT expansion of the bubble nucleation rate

Javier López Miras (Universidad de Granada)

10/22/26, 5:20 PM

The high-temperature effective field theory (3D EFT) approach to phase transitions relies on the assumption of a power counting which organizes the EFT expansion. Most studies truncate such expansions at superrenormalizable level, yet there is increasing evidence of the relevance of higher-dimensional corrections in the strong transition regime. A consistent treatment of such corrections,...

29. Hot news on the phase structure of the SMEFT

Luis Gil (Universidad de Granada)

10/22/26, 5:40 PM

In this talk I will discuss our recent advancements, and the technical challenges involved, in the precise determination of the high-temperature limit of the Standard Model Effective Field Theory (SMEFT). Through a comparison with lattice data, we provide evidence that the SMEFT may undergo a first-order phase transition even in the absence of direct modifications of the Higgs potential. In...