CERN Accelerating science

Preprint
Report number	CERN-TH-2024-198 ; KCL-PH-TH/2024-57 ; arXiv:2411.13641
Title	Bounds on the bubble wall velocity
Author(s)	Ai, Wen-Yuan (King's Coll. London) ; Laurent, Benoit (McGill U., Montreal (main)) ; van de Vis, Jorinde (CERN)
Document contact	Contact: arXiv
Imprint	2024-11-20
Number of pages	47
Note	47 pages, 8 figures
Subject category	astro-ph.CO ; Astrophysics and Astronomy ; hep-ph ; Particle Physics - Phenomenology
Abstract	Determining the bubble wall velocity in first-order phase transitions is a challenging task, requiring the solution of (coupled) equations of motion for the scalar field and Boltzmann equations for the particles in the plasma. The collision terms appearing in the Boltzmann equation present a prominent source of uncertainty as they are often known only at leading log accuracy. In this paper, we derive upper and lower bounds on the wall velocity, corresponding to the local thermal equilibrium and ballistic limits. These bounds are completely independent of the collision terms. For the ballistic approximation, we argue that the inhomogeneous plasma temperature and velocity distributions across the bubble wall should be taken into account. This way, the hydrodynamic obstruction previously observed in local thermal equilibrium is also present for the ballistic approximation. This is essential for the ballistic approximation to provide a lower bound on the wall velocity. We use a model-independent approach to study the behaviour of the limiting wall velocities as a function of a few generic parameters, and we test our developments in the singlet extended Standard Model.
Other source	Inspire
Copyright/License	preprint: (License: CC BY 4.0)