Bubble wall velocity from number density current in (non)equilibrium
Abstract
Cosmological first-order phase transitions (FOPTs) serve as comprehensive probes into our early Universe with associated generations of stochastic gravitational waves and superhorizon curvature perturbations or even primordial black holes. In characterizing the FOPT, phenomenological parameters like transition temperatures, strength factors, bubble separations, and energy budgets can be easily extracted from the macroscopic equilibrium features of the underlying particle physics models except for the terminal wall velocity of the bubble expansion, making it the last key parameter to be determined most difficultly due to the non-equilibrium nature of the microscopic transition model. In this paper, we propose a new model-independent approach to calculate the bubble wall velocity by virtue of an extra junction condition from the conservation and violation of the total number density current across the shock front (if any) and bubble wall, respectively.
Keywords
Cite
@article{arxiv.2409.20045,
title = {Bubble wall velocity from number density current in (non)equilibrium},
author = {Zi-Yan Yuwen and Jun-Chen Wang and Shao-Jiang Wang},
journal= {arXiv preprint arXiv:2409.20045},
year = {2024}
}
Comments
v2, 43 pages, 7 figures, major revision, a proof is added for the collision integral to vanish in local dynamical equilibrium, the necessity is introduced for the scalar-wall contribution to the total number density current, the clarification is emphasized for the conservation and violation of total number density current across the shock front and bubble wall, respectively