Polymer Quantization of the Isotropic Universe: comparison with the Bounce of Loop Quantum Cosmology

TL;DR

This paper explores polymer quantum mechanics applied to the isotropic universe, comparing two representations and their resulting bounce behaviors with Loop Quantum Cosmology, highlighting the dependence of bounce density on initial conditions.

Contribution

It introduces a polymer quantization approach using different variables and compares the resulting cosmological bounces with those in Loop Quantum Cosmology, emphasizing the role of initial conditions.

Findings

Bounce density depends on initial conditions in one representation.

Polymer quantization with volume variable yields an intrinsic bounce cutoff.

Comparison suggests the viability of the improved LQC scheme.

Abstract

We implement Polymer Quantum Mechanics on the Hamiltonian formulation of the isotropic Universe in both the representations of the standard Ashtekar-Barbero-Immirzi connection and of a new generalized coordinate conjugate to the Universe volume. The resulting dynamics is a bouncing cosmology; when quantizing the volume-like variable the Big Bounce is an intrinsic cut-off on the cosmological dynamics, while when using the standard connection the Bounce density results to be dependent on the initial conditions of the prepared wave packet. Then we compare the nature of the resulting Bounce with what emerges in Loop Quantum Cosmology, where the dependence of the critical density on the initial conditions is present when the minimum area eigenvalue is implemented in a comoving representation instead of the physical one. We conclude that, if one hand the preferable scenario should be a Big Bounce whose density depends on initial conditions in view of the privileged SU(2) character that the Ashtekar-Barbero-Immirzi connection possesses in the full Loop Quantum Gravity, on the other hand the equivalence demonstrated in the context of polymer cosmology can be a hint in favour of the viability of the improved scheme of Loop Quantum Cosmology even though it is not expressed through the privileged set of variables.