Cosmic evolution of dark energy in a generalized Rastall gravity

TL;DR

This paper introduces a generalized Rastall gravity model where dark energy arises from non-conservation of the stress-energy tensor, leading to a natural cosmic evolution through different eras and addressing the coincidence problem.

Contribution

It proposes a novel framework for cosmic evolution with non-conserved stress-energy, resulting in a dynamic attractor solution and alleviating the coincidence problem.

Findings

Cosmic evolution naturally includes radiation, matter, and dark energy eras.

The model's fate is insensitive to initial conditions, unlike standard ΛCDM.

Deviations from conservation are significant during rapid dark energy evolution.

Abstract

In this work, we propose a scheme for cosmic evolution in a generalized Rastall gravity. In our approach, the role of dark energy is taken by the non-conserved sector of the stress energy-momentum tensor. The resultant cosmic evolution is found to naturally consists of three stages, namely, radiation dominated, ordinary matter dominated, as well as dark energy and dark matter dominated eras. Furthermore, for the present model, it is demonstrated that the eventual fate of the Universe is mostly insensitive to the initial conditions, in contrast to the standard $\Lambda$CDM model. In particular, the solution displays the properties of a dynamic attractor, which is reminiscent of quintessence and k-essence models. Subsequently, the cosmic coincidence problem is averted. The amount of deviation from a conserved stress energy-momentum tensor is shown to be more remarkable during the period when the dark energy evolves more rapidly. On the other hand, the conservation law is largely restored for the infinite past and future. The implications of the present approach are addressed.