Abstract
The cosmological electroweak phase transition can be strongly first order in extended particle physics models. To accurately predict the speed and shape of the bubble walls during such a transition, Boltzmann equations for the CP-even fluid perturbations must be solved. We point out that the equations usually adopted lead to unphysical behavior of the perturbations, for walls traveling close to or above the speed of sound in the plasma. This is an artifact that can be overcome by more carefully truncating the full Boltzmann equation. We present an improved set of fluid equations, suitable for studying the dynamics of both subsonic and supersonic walls, of interest for gravitational wave production and electroweak baryogenesis.
Highlights
The electroweak phase transition in the early Universe is known to be a smooth crossover within the standard model (SM), given the measured value of the Higgs boson mass [1,2]
To determine v and other relevant properties of the bubble wall, within a given particle physics model, one must self-consistently solve for the perturbations to the fluid induced by the wall; these are needed to determine the frictional force acting on the wall, that brings it to a state of steady expansion
We argue that the apparent sound barrier is an artifact of a particular truncation of the Boltzmann equations for the fluid perturbations, and that sensible solutions exist for wall speeds up to v 1⁄4 1 by making a better choice
Summary
The electroweak phase transition in the early Universe is known to be a smooth crossover within the standard model (SM), given the measured value of the Higgs boson mass [1,2]. The addition of new particles coupling to the Higgs can turn it into a strongly first order phase transition, proceeding by the nucleation of bubbles of the true, electroweak symmetry breaking vacuum, in the initially symmetric plasma This possibility has been widely studied because of its potential for providing electroweak baryogenesis (EWBG) [3,4,5], and gravity waves that might be observable in the upcoming LISA experiment [6,7]. IV the solutions of the old and new formalisms are compared for a typical background wall profile, as a function of the wall velocity v Formulas for the coefficients of the new fluid equations are presented in the Appendix A, and the results of refined estimates for the collision terms are explained in Appendix B
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
