Kinematic anisotropies and pulsar timing arrays

TL;DR

This paper analytically investigates how pulsar timing arrays can detect kinematic anisotropies in the gravitational wave background, revealing new physics and polarization features through their response functions and detection strategies.

Contribution

It provides the first analytical determination of pulsar response functions to kinematic anisotropies, including effects of parity violation and polarization, and proposes detection strategies.

Findings

Response functions depend on pulsar configuration and relative motion.

Detection sensitivity varies with anisotropy features and polarization.

Strategies can distinguish different cosmological gravitational wave signals.

Abstract

Doppler anisotropies, induced by our relative motion with respect to the source rest frame, are a guaranteed property of stochastic gravitational wave backgrounds of cosmological origin. If detected by future pulsar timing array measurements, they will provide interesting information on the physics sourcing gravitational waves, which is hard or even impossible to extract from measurements of the isotropic part of the background only. We analytically determine the pulsar response function to kinematic anisotropies, including possible effects due to parity violation, to features in the frequency dependence of the isotropic part of the spectrum, as well as to the presence of extra scalar and vector polarizations. For the first time, we show how the sensitivity to different effects crucially depends on the pulsar configuration with respect to the relative motion among frames. Correspondingly, we propose examples of strategies of detection, each aimed at exploiting future measurements of kinematic anisotropies for characterizing distinct features of the cosmological gravitational wave background.