Theory and Numerics of Gravitational Waves from Preheating after Inflation

TL;DR

This paper develops a theoretical and numerical framework to calculate gravitational wave spectra from preheating after inflation, providing new insights into their characteristics and potential detectability.

Contribution

It introduces a novel analytical and numerical method for computing gravitational wave spectra from stochastic scalar fields in an expanding universe, applied specifically to preheating scenarios.

Findings

Analytical results for gravitational wave emission from stochastic media.

Numerical results for preheating after chaotic inflation that differ from previous studies.

Estimates of peak frequency and amplitude relevant for gravitational wave detection.

Abstract

Preheating after inflation involves large, time-dependent field inhomogeneities, which act as a classical source of gravitational radiation. The resulting spectrum might be probed by direct detection experiments if inflation occurs at a low enough energy scale. In this paper, we develop a theory and algorithm to calculate, analytically and numerically, the spectrum of energy density in gravitational waves produced from an inhomogeneous background of stochastic scalar fields in an expanding universe. We derive some generic analytical results for the emission of gravity waves by stochastic media of random fields, which can test the validity/accuracy of numerical calculations. We contrast our method with other numerical methods in the literature, and then we apply it to preheating after chaotic inflation. In this case, we are able to check analytically our numerical results, which differ significantly from previous works. We discuss how the gravity wave spectrum builds up with time and find that the amplitude and the frequency of its peak depend in a relatively simple way on the characteristic spatial scale amplified during preheating. We then estimate the peak frequency and amplitude of the spectrum produced in two models of preheating after hybrid inflation, which for some parameters may be relevant for gravity wave interferometric experiments.