Signature of polarized ultralight vector dark matter in pulsar timing arrays

TL;DR

This paper explores how ultralight vector dark matter affects pulsar timing arrays, revealing unique directional and polarization signatures that can help distinguish dark matter effects from gravitational waves.

Contribution

It introduces the impact of vector dark matter's polarization and anisotropy on pulsar timing residuals and derives angular correlation curves to identify dark matter signatures.

Findings

Vector dark matter causes directional pulsar timing residuals.

Circular polarization enhances the quadrupole correlation signature.

Derived correlation curves can differentiate dark matter from gravitational waves.

Abstract

We investigate observational signatures of ultralight vector dark matter with masses $m \sim 10^{-24}$-$10^{-22}$ eV in pulsar timing arrays, taking into account general polarization states of the vector field. We find that vector dark matter induces pulsar timing residuals with nontrivial directional dependence, reflecting the anisotropic property and polarization structure specific to vector dark matter, unlike scalar dark matter. We also derive angular correlation curves of the timing residuals. Intriguingly, circular polarization of the vector dark matter enhances the quadrupole nature of the correlation curve, resulting in a more notable bending of the Hellings-Downs curve. The derived correlation curves offer a useful means to distinguish gravitational wave and dark matter contributions and to probe the nature of dark matter.