Gravitational Particle Production and the Validity of Effective Descriptions in Loop Quantum Cosmology

TL;DR

This paper examines the validity of effective descriptions in Loop Quantum Cosmology by analyzing gravitational particle production and testing the test field approximation across different quantization approaches.

Contribution

It provides a consistency test for effective LQC models by evaluating the backreaction of gravitationally produced particles in various perturbation frameworks.

Findings

The energy density of produced particles can challenge the test field approximation.

Different LQC approaches show varying degrees of backreaction effects.

The analysis offers criteria to validate the use of effective descriptions in LQC.

Abstract

The effective approach in Loop Quantum Cosmology (LQC) has provided means to obtain predictions for observable quantities in LQC models. While an effective dynamics in LQC has been extensively considered in different scenarios, a robust demonstration of the validity of effective descriptions for the perturbative level still requires further attention. The consistency of the description adopted in most approaches requires the assumption of a test field approximation, which is limited to the cases in which the backreaction of the particles gravitationally produced can be safely neglected. Within the framework of LQC, some of the main approaches to quantize the linear perturbations are the dressed metric, the hybrid approaches and the closed/deformed algebra approach. Here, we analyze the consistency of the test field assumption in these frameworks by computing the energy density stored in the particles gravitationally produced compared to the background energy density. This analysis ultimately provides us with a consistency test of the effective descriptions of LQC.