Relic gravitons on Kasner-like branes

TL;DR

This paper studies how tensor perturbations, including massless and massive gravitons, are amplified in a brane-world cosmology with a Kasner-like brane in an AdS bulk, revealing unique features compared to de Sitter models.

Contribution

It provides an exact analysis of tensor perturbations on Kasner-like branes, highlighting the absence of a mass gap and the mass-dependent amplification of massive modes during inflation.

Findings

No mass gap in the spectrum unlike de Sitter models

Massive modes can be amplified during inflation

Amplitude of massive fluctuations depends on mass

Abstract

We discuss the cosmological amplification of tensor perturbations in a simple example of brane-world scenario, in which massless gravitons are localized on a higher-dimensional Kasner-like brane embedded in a bulk AdS background. Particular attention is paid to the canonical normalization of the quadratic action describing the massless and massive vacuum quantum fluctuations, and to the exact mass-dependence of the amplitude of massive fluctuations on the brane. The perturbation equations can be separated. In contrast to de Sitter models of brane inflation, we find no mass gap in the spectrum and no enhancement for massless modes at high curvature. The massive modes can be amplified, with mass-dependent amplitudes, even during inflation and in the absence of any mode-mixing effect.