Can tensor-scalar induced GWs dominate PTA observations ?

TL;DR

This paper investigates whether tensor-scalar induced gravitational waves could be the primary source of signals detected by pulsar timing arrays, considering constraints from multiple cosmological observations.

Contribution

It analyzes the impact of tensor-scalar induced gravitational waves on PTA data and explores their potential to dominate over supermassive black hole binaries as the source.

Findings

TSIGW could dominate PTA signals under certain conditions

Current data constrains the parameter space for primordial gravitational waves

Bayes factor favors TSIGW+PGW as a plausible explanation for PTA observations

Abstract

Observational constraints on small-scale primordial gravitational waves are considerably weaker than those on large scales. We focus on scenarios with significant primordial gravitational waves and curvature perturbations on small scales, studying the energy density spectrum of the second-order TSIGW. By leveraging current data from CMB, BAO, and PTA, combined with the SNR analysis of LISA, we can investigate how tensor-scalar induced gravitational waves affect observations on various scales, thus constraining the parameter space for primordial gravitational waves and curvature perturbations. The Bayes factor analysis suggests that TSIGW+PGW might be more likely to dominate current PTA observations compared to SMBHB.