Uncertainty budgets for bubble wall velocities in cosmological phase transitions

by Philipp Schicho (University of Geneva)

Thursday 20 Nov 2025, 10:00 → 11:00 Europe/Vienna

First-order cosmological phase transitions could have been central to early-universe phenomena such as baryogenesis and gravitational waves (GW). Predicting such GW signatures requires not only reliable equilibrium thermodynamics but also an accurate determination of the terminal velocity of the nucleated bubbles during the transition.

In this talk, I present progress towards quantifying the theoretical uncertainties of bubble wall velocities. Using the WallGo package [1] applied to extensions of the Standard Model, I will identify several order-one sources of uncertainty, including missing out-of-equilibrium species in the collision terms, treatments of thermal masses, inputs from thermal equilibrium such as the nucleation temperature, and ansatz choices for bubble profiles. By mapping out this uncertainty budget, I will highlight the most critical directions for improving the reliability of wall velocity, and thus GW predictions [2].

 

[1] A. Ekstedt, O. Gould, J. Hirvonen, B. Laurent, L. Niemi, P. Schicho, and J. van de Vis, How fast does the WallGo? A package for computing wall velocities in first-order phase transitions, JHEP 04, 101 (2025),[2411.04970].

[2] J. van de Vis, P. Schicho, L. Niemi, B. Laurent, J. Hirvonen, O. Gould, WallGo investigates: Theoretical uncertainties in the bubble wall velocity, [2510.27691].