Gravitational Waves from Fully General Relativistic Oscillon Preheating

TL;DR

This study uses full general relativity simulations to analyze gravitational wave production during oscillon preheating after inflation, revealing gauge effects and validating perturbative methods.

Contribution

It provides the first comprehensive comparison between full GR simulations and perturbative approaches for gravitational waves from oscillon preheating, clarifying gauge ambiguities.

Findings

Full GR simulations show gauge choice impacts GW spectra.

Perturbative methods are accurate except during strong gravitational effects.

Certain gauges can artificially enhance gravitational wave signals.

Abstract

As long-lived quasi-solitons from the fragmentation of a scalar condensate, oscillons may dominate the preheating era after inflation. During this period, stochastic gravitational waves can also be generated. We quantify the gravitational wave production in this period with simulations accounting for full general relativity to capture all possible non-perturbative effects. We compute the gravitational wave spectra across a range of choices of the oscillon preheating models and compare our results to a conventional perturbative approach on an FLRW background. We clarify the gauge ambiguities in computing induced gravitational waves from scenarios where dense non-perturbative objects such as oscillons are being formed. In particular, we find that the synchronous gauge tends to contain large artificial enhancements in the gravitational wave spectrum due to gauge modes if gravity plays an important role in the formation of the oscillons, while other gauge choices, such as the radiation gauge or a suitably chosen "1+log" gauge, can efficiently reduce the contributions of gauge modes. The full general relativistic simulations indicate that gravitational wave spectra obtained from the perturbative approach on the FLRW background are fairly accurate, except when oscillon formation induces strong gravitational effects, for which case there can be an order unity enhancement.