Cosmological singularities and modified theories of gravity

TL;DR

This paper investigates how perturbative modifications to Friedmann equations in alternative gravity theories can lead to cosmological singularities, analyzing the influence of key coefficients and providing practical examples.

Contribution

It introduces a perturbative framework for modified gravity theories affecting Friedmann equations, highlighting the role of specific coefficients in singularity formation.

Findings

At most two coefficients influence singularity outcomes.

Certain modifications can avoid or induce singularities.

Examples demonstrate the applicability of the perturbative approach.

Abstract

We consider perturbative modifications of the Friedmann equations in terms of energy density corresponding to modified theories of gravity proposed as an alternative route to comply with the observed accelerated expansion of the universe. Assuming that the present matter content of the universe is a pressureless fluid, the possible singularities that may arise as the final state of the universe are surveyed. It is shown that, at most, two coefficients of the perturbative expansion of the Friedman equations are relevant for the analysis. Some examples of application of the perturbative scheme are included.