Bubble Wall Velocity at Strong Coupling

Abstract

Using the holographic correspondence as a tool, we determine the steady-state velocity of expanding vacuum bubbles nucleated within chiral finite temperature first-order phase transitions occurring in strongly-coupled large $N$ QCD-like models. We provide general formulae for the friction force exerted by the plasma on the bubbles and for the steady-state velocity. In the top-down holographic description, the phase transitions are related to changes in the embedding of $Dq$-${\bar Dq}$ flavor branes probing the black hole background sourced by a stack of $N$ $Dp$-branes. We first consider the Witten-Sakai-Sugimoto $D4$-$D8$-$\bar D8$ setup, compute the friction force and deduce the equilibrium velocity. Then we extend our analysis to more general setups and to different dimensions. Finally, we briefly compare our results, obtained within a fully non-perturbative framework, to other estimates of the bubble velocity in the literature.