Fluid equations for fast-moving electroweak bubble walls

Understand

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.