Tensor Perturbations from Bounce Inflation Scenario in f(Q) Gravity

TL;DR

This paper develops a bounce inflation model within f(Q) gravity, analyzing tensor perturbations and primordial gravitational waves, revealing conditions for spectrum tilt and stability, with implications for future GW detection.

Contribution

It introduces a novel bounce inflation scenario in f(Q) gravity and thoroughly investigates tensor perturbations and their spectra, including stability and tilt conditions.

Findings

Tensor spectrum may have a positive tilt under stability conditions.

Primordial tensor spectrum can be nearly scale-invariant in LQC-like scenarios.

Enhanced gravitational wave amplitude possible in the model.

Abstract

In this paper, we construct a bounce inflation cosmological scenario in the framework of the modified symmetric teleparallel gravity, namely f(Q) theory, and investigate the tensor perturbations therein. As is well-known, the tensor perturbations generated in the very early Universe (inflation and pre-inflation regions) can account for the primordial gravitational waves (PGWs) that are to be detected by the next generation of GW experiments. We discuss the stability condition of the tensor perturbations in the bounce inflation process and investigate in detail the evolution of the perturbation variable. The general form of the tensor power spectrum is obtained both for large as well as small scale modes. As a result, we show for both kinds of modes (short or long wavelength modes), and the tensor spectrum may get a positive tilt in the parametric range where the tensor perturbation proves to be stable -- this interestingly hints an enhancement of gravitational waves' amplitude in the background of the f(Q) bounce-inflation scenario. Moreover, we study the LQC-like scenario as a specific case of our model, in which, the primordial tensor power spectrum turns out to be nearly scale-invariant on both small and large scales.