Enhancement of gravitational waves at Q-ball decay including non-linear density perturbations

TL;DR

This paper investigates how Q-ball decay-induced transitions in the early universe amplify second-order gravitational waves, aligning theoretical predictions with recent pulsar timing array observations.

Contribution

It extends previous analyses by including non-linear density perturbations, revealing enhanced gravitational wave production during Q-ball decay.

Findings

Gravitational wave spectrum can match PTA observations

Non-linear density perturbations significantly boost GW production

Transition from matter to radiation era impacts GW signals

Abstract

The existence of a stochastic gravitational wave background is indicated by the recent pulsar timing array (PTA) experiments. We study the enhanced production of second-order gravitational waves from the scalar perturbations when the universe experiences a transition from the early matter-dominated era to the radiation-dominated era due to Q-ball decay. We extend the analysis in previous work by including the frequency range where density perturbations go non-linear and find that the resultant gravitational wave spectrum can be consistent with that favored by the recent PTA experiment results.