Neutrino masses and gravitational wave background

TL;DR

This paper explores how a long-lived right-handed neutrino in the Standard Model can produce entropy that distorts the primordial gravitational wave background, offering a way to probe neutrino properties.

Contribution

It introduces a scenario where a suppressed Yukawa coupling right-handed neutrino affects gravitational wave spectra, linking neutrino mass to observable cosmological signals.

Findings

Long-lived neutrino causes entropy production.

Distortion in gravitational wave spectrum reveals neutrino mass.

Potential to measure the lightest neutrino mass through gravitational waves.

Abstract

We consider the Standard Model with three right-handed neutrinos to generate tiny neutrino masses by the seesaw mechanism. Especially, we investigate the case when one right-handed neutrino has the suppressed Yukawa coupling constants. Such a particle has a long lifetime and can produce an additional entropy by the decay. It is then discussed the impact of the entropy production on the gravitational wave background originated in the primordial inflation. We show that the mass and the coupling constants of the long-lived right-handed neutrino can be probed by the distortion of the gravitational wave spectrum, leading to the information of the mass of the lightest active neutrino.