Scalar-Induced Gravitational Waves in Modified Gravity

TL;DR

This paper investigates how scalar-induced gravitational waves behave in f(R) gravity, revealing that modifications to General Relativity can leave observable signatures in the low-frequency gravitational wave spectrum, aiding in testing gravity theories.

Contribution

It extends the analysis of scalar-induced gravitational waves from General Relativity to f(R) gravity, exploring their spectral behavior across a wide frequency range.

Findings

Beyond-GR corrections affect low-frequency SIGW spectrum

Potential to constrain modified gravity using gravitational wave observations

Spectrum deviations are detectable with current and future detectors

Abstract

Scalar-Induced Gravitational Waves (SIGWs), second-order tensor modes sourced by first-order scalar fluctuations in General Relativity (GR), are expected to contribute to the Stochastic Gravitational Wave Background (SGWB) potentially detectable by current and future gravitational wave interferometers. In the framework of GR, this SGWB represents an unavoidable contribution to the gravitational wave spectrum. In this paper, we go beyond GR and we investigate the behavior of SIGWs in f(R) gravity. We explore how the SIGW spectrum is influenced across a broad range of frequencies, from the nano-Hz regime, where the Pulsar Timing Array (PTA) operates, through the milli-Hz band probed by the space-based LISA detector, up to the kilo-Hz frequency range, where the ground-based LIGO/Virgo/KAGRA network is currently operational. Our results indicate that the beyond-GR correction leaves an observational imprint, mainly in the low-frequency part of the spectrum, giving the possibility to use SIGW to constrain GR on scales on which we have limited information.