Bubble expansion at strong coupling
Li Li, Shao-Jiang Wang, Zi-Yan Yuwen
Abstract
The cosmological first-order phase transition (FOPT) can be of strong dynamics, but its bubble wall velocity is difficult to determine due to the lack of detailed collision terms. Recent holographic numerical simulations of strongly coupled theories with an FOPT prefer a relatively small wall velocity linearly correlated with the phase pressure difference between false and true vacua for a planar wall. In this article, we analytically reveal the nonrelativistic limit of a planar/cylindrical/spherical wall expansion of a bubble strongly interacting with the thermal plasma. The planar-wall result reproduces the linear relation found previously in the holographic numerical simulations. The results for cylindrical and spherical walls can be directly tested in future numerical simulations. Once confirmed, the bubble wall velocity for a strongly coupled FOPT can be expressed purely in terms of the hydrodynamics without invoking the underlying microphysics.