The bubble wall velocity in the minimal supersymmetric light stop scenario

TL;DR

This paper calculates the bubble wall velocity during a first-order electroweak phase transition in the MSSM's light stop scenario, using a 2-loop potential and a simplified plasma interaction model, finding very slow wall velocities.

Contribution

It provides a refined calculation of the bubble wall velocity in the MSSM's light stop scenario using a 2-loop thermal potential and an extrapolated friction parameter.

Findings

Wall velocity around 0.05, much below the speed of sound.

Phase transition strength about 10% greater than previous estimates.

Results consistent with earlier 1-loop calculations.

Abstract

We build on existing calculations of the wall velocity of the expanding bubbles of the broken symmetry phase in a first-order electroweak phase transition within the light stop scenario (LSS) of the MSSM. We carry out the analysis using the 2-loop thermal potential for values of the Higgs mass consistent with present experimental bounds. Our approach relies on describing the interaction between the bubble and the hot plasma by a single friction parameter, which we fix by matching to an existing 1-loop computation and extrapolate it to our regime of interest. For a sufficiently strong phase transition (in which washout of the newly-created baryon asymmetry is prevented) we obtain values of the wall velocity, v_w~0.05, far below the speed of sound in the medium, and not very much deviating from the previous 1-loop calculation. We also find that the phase transition is about 10% stronger than suggested by simply evaluating the thermal potential at the critical temperature.