Constraining fundamental constant variations from ultralight dark matter with pulsar timing arrays

Pulsar timing arrays (PTAs) are exceptionally sensitive detectors in the frequency band nHz ? f ? mu Hz. Ultralight dark matter (ULDM), with mass in the range 10(-23) eV ? m(phi) ? 10(-20) eV, is one class of DM models known to generate signals in this frequency window. While purely gravitational signatures of ULDM have been studied previously, in this work we consider two signals in PTAs which arise in the presence of direct couplings between ULDM and ordinary matter. These couplings induce variations in fundamental constants, i.e., particle masses and couplings. These variations can alter the moment of inertia of pulsars, inducing pulsar spin fluctuations via conservation of angular momentum, or induce apparent timing residuals due to reference clock shifts. By using mock data mimicking current PTA datasets, we show that PTA experiments outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons. In the case of coupling to quarks or photons, we find that PTAs and atomic clocks set similar constraints. Additionally, we discuss how future PTAs can further improve these constraints, and detail the unique properties of these signals relative to the previously studied effects of ULDM on PTAs.

Automated summary

Pulsar timing arrays (PTAs) are sensitive detectors in the frequency range of nHz to μHz that can detect ultralight dark matter (ULDM) signals. This study investigates the signals in PTAs that arise from direct couplings between ULDM and ordinary matter, which induce variations in fundamental constants and affect pulsar spin and timing residuals. Mock data resembling current PTA datasets is used to demonstrate that PTA experiments can provide better constraints for ULDM coupled to electrons, muons, or gluons compared to torsion balance and atomic clock constraints. The study also discusses potential improvements in future PTAs and highlights the unique properties of these signals.