The evolution of tensor perturbations in scalar-tensor theories of gravity

TL;DR

This paper derives the evolution equations for tensor perturbations in scalar-tensor gravity theories, providing exact solutions for certain models and showing that gravitational attraction prevents amplification of tensor modes.

Contribution

It presents the first detailed derivation of tensor perturbation equations in generic scalar-tensor theories and offers exact solutions for specific backgrounds.

Findings

Tensor perturbation evolution depends on theory parameters

No amplification occurs if gravitational interaction is attractive

Exact solutions are obtained for Friedmann-Lemaître-Robertson-Walker backgrounds

Abstract

The evolution equations for tensor perturbations in a generic scalar tensor theory of gravity are presented. Exact solution are given for a specific class of theories and Friedmann-Lema\^{i}tre-Robertson-Walker backgrounds. In these cases it is shown that, although the evolution of tensor models depends on the choice of parameters of the theory, no amplification is possible if the gravitational interaction is attractive.