Analog gravity in nonisentropic fluids

TL;DR

This paper extends the concept of analog gravity to nonisentropic fluids by deriving conditions under which the acoustic metric applies beyond the traditional isentropic assumption, highlighting special cases where standard analog metrics are recovered.

Contribution

It demonstrates that the usual acoustic metric can be derived for nonisentropic fluids within a Lagrangian framework under specific conditions, broadening the scope of analog gravity models.

Findings

Analog metric derivation for nonisentropic fluids

Special case with pressure form reproduces standard acoustic metric

Conditions for nonadiabatic perturbations to be neglected

Abstract

The analog acoustic metric has been originally derived for adiabatic acoustic perturbations propagating in an isentropic irrotational ideal fluid. In the framework of a Lagrangian hydrodynamic description we demonstrate that under certain conditions the usual acoustic metric can be derived for nonisentropic fluids. In a special case when the pressure takes a special form and the nonadiabatic perturbations are neglected the adiabatic acoustic perturbations corresponding to massless phonons propagate in an analog metric of the usual type.