Forms of action for perfect fluid in General Relativity and mimetic gravity

TL;DR

This paper explores different action formulations for perfect fluids in General Relativity, including a new action for mimetic gravity that accommodates vorticity, enhancing the theoretical modeling of such fluids.

Contribution

It introduces new action forms for perfect fluids, including a novel action for mimetic gravity that allows vorticity, expanding the theoretical framework.

Findings

Derived equivalent actions for perfect fluids with and without pressure.

Generalized actions to include vorticity in fluid motion.

Proposed a new action for mimetic gravity enabling vorticity in mimetic matter.

Abstract

We consider various forms of action allowing us to describe a perfect fluid in the framework of General Relativity. First we consider a potential motion without pressure. Starting from an action in terms of the current density vector built similarly to the action of a single particle, we build a series of equivalent actions through various changes of variables. The results are then generalized to the cases of motion with vorticity and the presence of pressure. The obtained forms of action are compared to the previously known variants. We discuss the possibilities to use the obtained results to formulate the theories containing a description of a perfect fluid. A new form of action is proposed for mimetic gravity, which allows a motion with vorticity for mimetic matter as a perfect fluid.