Pulsar Timing Arrays and Gravity Tests in the Radiative Regime

TL;DR

This paper develops a comprehensive framework for testing gravity theories in the radiative regime using pulsar timing arrays, considering massive gravitons and alternative polarization modes to identify characteristic signals.

Contribution

It extends existing methods by including dispersive polarization modes and graviton mass effects, enabling more detailed tests of gravity theories with pulsar timing data.

Findings

New calculations of Hellings-Downs functions for dispersive modes

Potential to detect polarization modes and graviton mass

Framework for future gravitational wave experiments

Abstract

In this paper, we focus on testing gravity theories in the radiative regime using pulsar timing array observations. After reviewing current techniques to measure the dispersion and alternative polarization of gravitational waves, we extend the framework to the most general situations, where the combinations of a massive graviton and alternative polarization modes are considered. The atlas of the Hellings-Downs functions is completed by the new calculations for these dispersive alternative polarization modes. We find that each mode and corresponding graviton mass introduce characteristic features in the Hellings-Downs function. Thus, in principal, we can not only detect each polarization mode, measure the corresponding graviton mass, but also discriminate the different scenarios. In this way, we can test gravity theories in the radiative regime in a generalized fashion, and such method is a direct experiment, where one can address the gauge symmetry of the gravity theories in their linearised limits. Although current pulsar timing still lacks enough stable pulsars and sensitivity for such practices, we expect that future telescopes with larger collecting area could make such experiments be feasible.