Superbounce and Loop Quantum Cosmology Ekpyrosis from Modified Gravity

TL;DR

This paper explores how specific $F(R)$ modified gravity theories can produce bouncing cosmologies, including superbounce and ekpyrotic models, and examines their properties and implications for accelerating universes.

Contribution

It reconstructs $F(R)$ theories that generate bouncing cosmologies, revealing new models that lead to acceleration at large curvatures, and analyzes their mathematical properties.

Findings

Both models yield power law $F(R)$ gravities.

Models lead to accelerating cosmologies at large curvature.

Mathematical analysis of spacetime symmetries.

Abstract

As is known, in modified cosmological theories of gravity many of the cosmologies which could not be generated by standard Einstein gravity, can be consistently described by $F(R)$ theories. Using known reconstruction techniques, we investigate which $F(R)$ theories can lead to a Hubble parameter describing two types of cosmological bounces, the superbounce model, related to supergravity and non-supersymmetric models of contracting ekpyrosis and also the Loop Quantum Cosmology modified ekpyrotic model. Since our method is an approximate method, we investigate the problem at large and small curvatures. As we evince, both models yield power law reconstructed $F(R)$ gravities, with the most interesting new feature being that both lead to accelerating cosmologies, in the large curvature approximation. The mathematical properties of the some Friedmann-Robertson-Walker spacetimes $M$, that describe superbounce-like cosmologies are also pointed out, with regards to the group of curvature collineations $CC(M)$.