The behavior of non-linear anisotropies in bouncing Bianchi I models of loop quantum cosmology

TL;DR

This paper investigates how anisotropies affect the bounce in loop quantum cosmology, showing that anisotropic shear remains finite and the universe isotropizes after the bounce, confirming the robustness of the big bounce scenario.

Contribution

It demonstrates that the big bounce persists in anisotropic Bianchi I models within loop quantum cosmology, with anisotropies remaining finite and decaying post-bounce.

Findings

Anisotropic shear grows during collapse but stays finite through the bounce.

Post-bounce, anisotropies decay and the universe becomes isotropic.

The big bounce scenario remains valid even with anisotropies.

Abstract

In homogeneous and isotropic loop quantum cosmology, gravity can behave repulsively at Planckian energy densities leading to the replacement of the big bang singularity with a big bounce. Yet in any bouncing scenario it is important to include non-linear effects from anisotropies which typically grow during the collapsing phase. We investigate the dynamics of a Bianchi I anisotropic model within the framework of loop quantum cosmology. Using effective semi-classical equations of motion to study the dynamics, we show that the big bounce is still predicted with only differences in detail arising from the inclusion of anisotropies. We show that the anisotropic shear term grows during the collapsing phase, but remains finite through the bounce. Immediately following the bounce, the anisotropies decay and with the inclusion of matter with equation of state $w < +1$, the universe isotropizes in the expanding phase.