Gravitational wave stochastic background from cosmological particle decay

TL;DR

This paper explores the gravitational wave background generated by decaying dark matter particles in the early universe, predicting a flat spectrum that could dominate at high frequencies and discussing its potential observability.

Contribution

It introduces a model where decaying dark matter produces a stochastic GW background with a flat spectrum, including a novel calculation of the decay's direct contribution.

Findings

The GW background is frequency independent (flat) across a broad spectrum.

The background may dominate at frequencies above 10 GHz.

Decay of Planck-mass particles into gravitons contributes to the GW spectrum.

Abstract

We assume that the cosmological dark matter is composed of massive neutral scalar particles that decay into two massless particles. The decay produces a stochastic background of gravitational waves (GWs) via a 'memory effect' mechanism. We calculate the spectral amplitude and slope of the resulting background, which is frequency independent (flat). We discuss its potential observability and show that the resulting background might dominate the cosmological GW background at frequencies above about 10 GHz. Penrose has proposed a cosmological model in which dark matter particles have the Planck mass and decay into two gravitons. For these, the spectrum has an additional 'direct' contribution from the decay products, which we also calculate. At low frequencies, this direct contribution also has a flat spectrum but with a much smaller amplitude than the memory part.