Impact of Non-Thermal Leptogenesis with Early Matter Domination on Gravitational Waves from First-order Phase Transition

TL;DR

This paper explores how non-thermal leptogenesis during an early matter-dominated era affects gravitational wave signals from a first-order phase transition, offering potential observational signatures for future detectors.

Contribution

It introduces a novel scenario where early matter domination and entropy injection modify gravitational wave spectra, linking leptogenesis with GW observations.

Findings

GW spectrum shows damping and frequency shifts due to early matter domination.

Parameter space identified where non-thermal leptogenesis produces observable GW signals.

Future detectors like ET, DECIGO, and BBO can potentially detect these signatures.

Abstract

We study the impact of non-thermal leptogenesis on the spectrum of gravitational waves (GWs) produced by a strong first-order phase transition in the early Universe. We consider a scenario in which a heavy scalar field, $\phi$, dominates the energy density of the early Universe and decays into heavy right-handed neutrinos (RHNs). The subsequent decay of RHNs generates a lepton asymmetry, which is partially converted into the observed baryon asymmetry via the sphaleron process. The $\phi$-dominated era and the entropy injection from the decays of $\phi$ and RHNs leave characteristic imprints on the GW spectrum, such as damping and modified frequency dependence, that distinguish it from the standard cosmological evolution. We identify the parameter space in which non-thermal leptogenesis is successful, leading to distinctive GW spectral features. We show that these GW signals can fall within the sensitivity ranges of future detectors such as ET, DECIGO and BBO. If observed, they would provide valuable insights into the thermal history and dynamics of the early Universe.