Non-linear metric perturbation enhancement of primordial gravitational waves

TL;DR

This paper investigates how non-linear effects during preheating after inflation can significantly amplify primordial gravitational waves, potentially improving their detectability.

Contribution

It demonstrates that non-linear metric perturbations during preheating enhance the gravitational wave background beyond linear predictions.

Findings

Preheating induces a significant increase in gravitational wave energy density.

Scalar mode preheating affects vector and tensor mode evolution.

Enhanced gravitational wave background could improve detection prospects.

Abstract

We present the evolution of the full set of Einstein equations during preheating after inflation. We study a generic supersymmetric model of hybrid inflation, integrating fields and metric fluctuations in a 3-dimensional lattice. We take initial conditions consistent with Eintein's constraint equations. The induced preheating of the metric fluctuations is not large enough to backreact onto the fields, but preheating of the scalar modes does affect the evolution of vector and tensor modes. In particular, they do enhance the induced stochastic background of gravitational waves during preheating, giving an energy density in general an order of magnitude larger than that obtained by evolving the tensors fluctuations in an homogeneous background metric. This enhancement can improve the expectations for detection by planned gravitational waves observatories.