Critical velocity of a homogeneous condensate ($v_L=\sqrt{\mu /m}$)

For a repulsive homogeneous condensate with Bogoliubov energy $E(p)=\sqrt{(p^2/2m)(p^2/2m+2\mu )}$, the infimum of $E(p)/p$ is the speed of sound $\sqrt{\mu /m}$. This is energetic stability against the given bulk modes, not a universal measured dissipation threshold.