Chaplygin gas and effective description of inhomogeneous universe models in general relativity

TL;DR

This paper explores a novel inhomogeneous cosmology model in general relativity where the Chaplygin gas equation of state describes both dark energy and dark matter as manifestations of spatial geometry, challenging standard cosmological assumptions.

Contribution

It introduces a model where inhomogeneous properties obey the Chaplygin equation of state, unifying dark energy and dark matter as geometric effects rather than separate entities.

Findings

Effective Einstein equations describe scale-dependent inhomogeneous cosmologies.

The model suggests dark energy and dark matter can be geometric in origin.

Standard Chaplygin gas remains compatible with observational constraints.

Abstract

In the framework of spatially averaged inhomogeneous cosmologies in classical general relativity, effective Einstein equations govern the dynamics of averaged scalar variables in a scale--dependent way. A particular cosmology may be characterized by a cosmic equation of state, closing the hierarchy of effective equations. In this context a natural candidate is provided by the Chaplygin gas, standing for a unified description of dark energy and dark matter. In this paper, we suppose that the inhomogeneous properties of matter and geometry obey the Chaplygin equation of state. The most extreme interpretation assumes that both dark energy and dark matter are not included as additional sources, but are both manifestations of spatial geometrical properties. This feature is an important conceptual difference in comparison with the standard approach of a Friedmann-Lema\^itre-Robertson-Walker universe filled with dust and another fundamental field characterized by the Chaplygin equation of state. We finally discuss the consequences of the resulting scenario for effective cosmological parameters in order to establish the framework of a future confrontation with observations, and we note that the standard Chaplygin gas may not be ruled out by them.