Singularity-free and non-chaotic inhomogeneous Mixmaster in polymer representation for the volume of the universe

TL;DR

This paper demonstrates that polymer quantization of the inhomogeneous Mixmaster model results in a non-chaotic, singularity-free cosmological evolution with a bounce, linking quasi-isotropic inflationary phases to stable Kasner regimes.

Contribution

It introduces a polymer quantum framework for the inhomogeneous Mixmaster model, showing the removal of chaos and singularities in the universe's evolution.

Findings

Singularity is avoided due to bounded curvature.

The universe undergoes a bounce instead of a Big Bang singularity.

The model exhibits a transition from oscillatory to Kasner-like regimes.

Abstract

We analyze the semiclassical polymer dynamics of the inhomogeneous Mixmaster model by choosing the cubed scale factor as the discretized configurational variable, while the anisotropies remain pure Einsteinian variables. Such a modified theory of gravity should be regarded as the appropriate framework to describe the behavior of quantum mean values, both in polymer quantum mechanics and in Loop Quantum Cosmology. We first construct the generalized Kasner solution, including a massless scalar field and a cosmological constant in the dynamics. They account for a quasi-isotropization, inflationary-like mechanism. The resulting scenario links a singularity-free Kasner-like regime with a homogeneous and isotropic de Sitter phase. Subsequently, we investigate the role of the three-dimensional scalar curvature, demonstrating that a bounce of the point-universe against the potential walls can always occur within the polymer framework, also in the presence of a scalar field. However, the absence of the singularity implies that the curvature is bounded. Therefore, the point-universe undergoes an oscillatory regime until it oversteps the potential walls (if the Big Bounce is not reached before). After that, a final stable Kasner-like regime will last all the way toward the Big Bounce. Thus, the present study demonstrates that, as soon as a discretization of the volume of the universe is performed, the generic cosmological solution is non-chaotic and free from singularities. It is likely that the same result can be achieved also in the loop quantum cosmology approach.