Confronting sound speed resonance with pulsar timing arrays

TL;DR

This paper explores whether the recent pulsar timing array signals can be explained by gravitational waves generated through a sound speed resonance mechanism linked to primordial curvature perturbations, using combined PTA data.

Contribution

It demonstrates that the observed stochastic signal can be attributed to gravitational waves sourced by sound speed resonance, providing specific oscillation frequency and start time ranges.

Findings

The stochastic signal aligns with gravitational waves from sound speed resonance.

Oscillation frequency range identified as [1.51, 4.90] x 10^-7 Hz.

Start time of oscillation estimated between 2.05 and 106 x 10^7 seconds.

Abstract

The stochastic signal detected by pulsar timing arrays (PTAs) has raised great interest in understanding its physical origin. Assuming the signal is a cosmological gravitational-wave background produced by overly large primordial curvature perturbations, we investigate the sound speed resonance effect with an oscillatory behavior using the combined PTA data from NANOGrav 15-yr data set, PPTA DR3, and EPTA DR2. We find that the stochastic signal can be explained by the induced gravitational waves sourced by the sound speed resonance mechanism, with the oscillation frequency $f_* \in [1.51, 4.90] \times 10^{-7}$Hz and the start time of oscillation $|\tau_0| \in [2.05, 106] \times 10^7$s