Deformed Matter Bounce with Dark Energy Epoch

TL;DR

This paper extends Loop Quantum Cosmology's matter bounce model to include a dark energy epoch ending in a Rip singularity, revealing potential limitations of LQC near singularities and suggesting the need for a more fundamental quantum gravity theory.

Contribution

It introduces a deformed matter bounce scenario with a dark energy era ending in a Rip singularity, highlighting the limitations of LQC near such singularities and exploring realization via viscous fluid and scalar field.

Findings

Dark energy era can be quintessence-like or phantom.

Rip singularity occurs where scale factor and Hubble rate diverge.

Effective energy density and pressure become complex at the singularity.

Abstract

We extend the Loop Quantum Cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a Rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario", the Universe is contracting from an initial non-causal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, thus the model is described by a dark energy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the dark energy era is quintessential like which follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the dark energy era, a Rip singularity exists, where the scale factor and Hubble rate diverge, however the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, firstly that the ordinary Loop Quantum Cosmology matter bounce evolution stops, thus ending the infinite repetition of the ordinary matter bounce scenario. Secondly, the fact that both the pressure and the density become complex indicates probably that the description of the cosmic evolution within the theoretical context of Loop Quantum Cosmology, ceases to describe the physics of the system and possibly a more fundamental theory of quantum gravity is needed near the would be Rip singularity. We describe the qualitative features of the model and we also investigate how this cosmology could be realized by a viscous fluid and scalar field in the context of LQC.