Bubble Wall Velocity at Strong Coupling
  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.
