Tensor perturbations in high-curvature string backgrounds

TL;DR

This paper derives a generalized evolution equation for tensor perturbations in string cosmology, incorporating higher-curvature effects and dilaton coupling, and analyzes their impact on the perturbation spectrum.

Contribution

It introduces a first-order $'$ corrected tensor perturbation equation in string backgrounds, accounting for higher-curvature and dilaton effects.

Findings

Higher-curvature corrections slightly modify the perturbation spectrum.

Modifications are negligible when the background curvature remains constant.

The derived equation extends previous models by including string-specific effects.

Abstract

We derive a generalized equation for the evolution of tensor perturbations in a cosmological background, taking into account higher-curvature contributions and a tree-level coupling to the dilaton in the string frame. The equation is obtained by perturbing the gravi-dilaton string effective action, expanded up to first order in $\alpha'$. The $\alpha'$ corrections can modify the low-energy perturbation spectrum, but the modifications are shown to be small when the background curvature keeps constant in the string frame.