Gauge Independence of Induced Gravitational Waves

TL;DR

This paper investigates whether the observable induced gravitational waves are gauge-independent during the radiation era, finding they are consistent across different gauges, contrary to some previous claims.

Contribution

It demonstrates that late-time induced gravitational waves are gauge-invariant in the radiation era, clarifying a debated issue in the literature.

Findings

Observable GWs are gauge-independent in the radiation era.

Contradicts previous claims of gauge dependence.

Provides interpretation of gauge dependence in induced GWs.

Abstract

We study gauge (in)dependence of the gravitational waves (GWs) induced from curvature perturbations. For the GWs produced in a radiation-dominated era, we find that the observable (late-time) GWs in the TT gauge and in the Newtonian gauge are the same in contrast to a claim in the literature. We also mention the interpretation of the gauge dependence of the tensor perturbations which appears in the context of the induced GWs.