Gravitational wave production from preheating: parameter dependence

TL;DR

This paper derives an analytical formula for gravitational wave amplitude dependence on the resonance parameter q during preheating, validated by simulations, enabling predictions of GW signals across various scenarios.

Contribution

It provides the first analytical derivation of GW amplitude dependence on q, applicable to any preheating scenario, with numerical validation and simple predictive fits.

Findings

GW amplitude can reach up to 10^{-11} in energy density.

GW peak frequency is typically above 10^7 Hz.

The parametrization predicts GW background characteristics for arbitrary q.

Abstract

Parametric resonance is among the most efficient phenomena generating gravitational waves (GWs) in the early Universe. The dynamics of parametric resonance, and hence of the GWs, depend exclusively on the resonance parameter $q$. The latter is determined by the properties of each scenario: the initial amplitude and potential curvature of the oscillating field, and its coupling to other species. Previous works have only studied the GW production for fixed value(s) of $q$. We present an analytical derivation of the GW amplitude dependence on $q$, valid for any scenario, which we confront against numerical results. By running lattice simulations in an expanding grid, we study for a wide range of $q$ values, the production of GWs in post-inflationary preheating scenarios driven by parametric resonance. We present simple fits for the final amplitude and position of the local maxima in the GW spectrum. Our parametrization allows to predict the location and amplitude of the GW background today, for an arbitrary $q$. The GW signal can be rather large, as $h^2\Omega_{\rm GW}(f_p) \lesssim 10^{-11}$, but it is always peaked at high frequencies $f_p \gtrsim 10^{7}$ Hz. We also discuss the case of spectator-field scenarios, where the oscillatory field can be e.g.~a curvaton, or the Standard Model Higgs.