Thermodynamic stability of superflows in general relativity and Newtonian gravity

Abstract

Landau’s criterion for superfluidity is a special case of a broader principle: A moving fluid cannot be stopped by frictional forces if its state of motion is a local minimum of the grand potential. We employ this general thermodynamic criterion to derive a set of inequalities that any superfluid mixture (with an arbitrary number of order parameters) must satisfy for a certain state of motion to be long-lived and unimpeded by friction. These macroscopic constraints complement Landau’s original criterion, in that they hold at all temperatures, and remain valid even for gapless superfluids. They are only necessary conditions for the existence of a frictionless hydrodynamic motion, since they presuppose the validity of a fluid description, but they provide sufficient conditions for stability against stochastic hydrodynamic fluctuations. We first formulate our analysis within General Relativity (with neutron star applications in mind), and then we take the Newtonian limit.