Testing gravity with cosmic variance-limited pulsar timing array correlations

TL;DR

This paper demonstrates that cosmic variance-limited pulsar timing array measurements of the gravitational wave background can effectively distinguish general relativity from alternative gravity theories by analyzing the angular power spectrum.

Contribution

It highlights the importance of power spectrum measurements in PTAs for testing gravity, emphasizing the potential of noise-free correlation data to differentiate gravitational theories.

Findings

Cosmic variance-limited measurements can distinguish gravity theories.

Power spectrum multipoles are crucial for PTA precision.

PTAs can test gravity in the nanohertz GW regime.

Abstract

The nanohertz stochastic gravitational wave background (SGWB) is an excellent early universe laboratory for testing the fundamental properties of gravity. In this letter, we elucidate on the full potential of pulsar timing array (PTA) by utilizing cosmic variance-limited, or rather experimental noise-free, correlation measurements to understand the SGWB and by extension gravity. We show that measurements of the angular power spectrum play a pivotal role in the PTA precision era for scientific inferencing. In particular, we illustrate that cosmic variance-limited measurements of the first few power spectrum multipoles enable us to clearly set apart general relativity from alternative theories of gravity. This ultimately conveys that PTAs can be most ambitious for testing gravity in the nanohertz GW regime by zeroing in on the power spectrum.