Cosmological perfect fluids in higher-order gravity

TL;DR

This paper proves that higher-order gravity theories in certain cosmological spacetimes can be represented as perfect fluids, facilitating the modeling of dark energy effects as curvature contributions.

Contribution

It establishes that all higher-order gravitational corrections in specified spacetimes behave as perfect fluids, enabling new approaches to dark energy modeling.

Findings

Higher-order gravity corrections take the form of perfect fluids.

This result applies to Robertson-Walker and generalized Robertson-Walker spacetimes.

Facilitates treating dark energy as a curvature effect.

Abstract

We prove that in Robertson-Walker space-times (and in generalized Robertson-Walker spacetimes of dimension greater than 3 with divergence-free Weyl tensor) all higher-order gravitational corrections of the Hilbert-Einstein Lagrangian density $F(R,\square R, ... , \square^k R)$ have the form of perfect fluids in the field equations. This statement definitively allows to deal with dark energy fluids as curvature effects.