The nature of cosmological metric perturbations in presence of gravitational particle production

TL;DR

This paper investigates metric perturbations during a de Sitter phase with radiation caused by gravitational particle production, revealing significant differences from standard inflation and highlighting challenges in quantization.

Contribution

It provides explicit calculations of metric perturbations in such a de Sitter phase, demonstrating how particle production alters their evolution and the difficulties in setting initial conditions.

Findings

Scalar perturbation spectrum grows exponentially at small scales

Differences in perturbation evolution compared to standard inflation

Quantization of modes is complex and requires model modifications

Abstract

The present paper tries to answer the question: Can a de Sitter phase in presence of radiation be a competitor of the standard inflationary paradigm for the early universe? This kind of a de Sitter phase can exist in cosmological models where gravitational particle production takes place. To address the issue the metric perturbations in the de Sitter phase in presence of radiation must be known. The evolution of metric perturbations are explicitly calculated in the paper. It is seen that the evolution of scalar and vector perturbations are considerably different from standard inflationary models. These differences arise due to the particle production mechanism. The scalar perturbation power spectrum grows exponentially at small length scales. However, one cannot uniquely specify the scale at which this exponential growth starts because of the dependence of the power spectrum on the initial perturbation value. The time slice on which the initial perturbation starts is arbitrary. The arbitrariness of the initial time slice is related to the problem of setting the initial condition on the perturbations in the present model. The paper briefly opines on vector and tensor perturbations in the de Sitter space filled with radiation. It is seen that quantization of the perturbation modes in the present model is considerably difficult. One has to modify the present model to provide a consistent scheme of quantization of the perturbation modes.