Gravitational waves from supermassive right-handed neutrinos produced at preheating

TL;DR

This paper explores how supermassive right-handed neutrinos produced during preheating can generate a gravitational wave background, offering a new observational window into high-scale physics beyond the Standard Model.

Contribution

It introduces a mechanism where non-perturbative production of supermassive neutrinos during preheating sources gravitational waves, linking high-scale particle physics to observable signals.

Findings

Gravitational wave spectrum encodes information about supermassive neutrinos.

Preheating can efficiently produce heavy particles beyond the inflaton mass.

The resulting GW background can serve as a probe of high-scale physics.

Abstract

The post-inflationary production of supermassive particles can have profound implications for the thermal history of the universe and may leave observable imprints in the gravitational wave (GW) background. In scenarios where the inflaton couples predominantly to heavy fields, say right-handed neutrino (RHN), non-perturbative mechanisms such as parametric resonance can lead to their efficient production, even when their masses exceed the inflaton mass. Once produced, the RHNs emit gravitons through bremsstrahlung as they decay into the Standard Model (SM) particles via $N\rightarrow \ell + H$, enabled by the unavoidable minimal coupling to gravity, sourcing a stochastic GW background. We study this mechanism within the framework of $\alpha-$attractor inflationary models, highlighting how the resulting GW spectrum carries indirect imprints of the heavy sector and the post-inflationary dynamics. This offers an observational window into otherwise inaccessible supermassive particles and provides a powerful probe of high-scale physics beyond the SM.