Constraining Fundamental Constant Variations from Ultralight Dark Matter with Pulsar Timing Arrays

TL;DR

This paper explores how pulsar timing arrays can detect or constrain ultralight dark matter that interacts with standard particles by causing variations in fundamental constants, surpassing some existing experimental limits.

Contribution

It introduces new PTA-based methods to constrain ULDM couplings to matter, considering direct interactions affecting fundamental constants and comparing with existing experimental bounds.

Findings

PTAs outperform torsion balance and atomic clocks for certain ULDM couplings.

Future PTAs can significantly tighten constraints on ULDM interactions.

Distinct signals from ULDM couplings can be identified in pulsar timing data.

Abstract

Pulsar Timing Arrays (PTAs) are exceptionally sensitive detectors in the frequency band $\text{nHz} \lesssim f \lesssim \mu\text{Hz}$. Ultralight dark matter (ULDM), with mass in the range $10^{-23}\,\text{eV} \lesssim m_\phi \lesssim 10^{-20}\,\text{eV}$, 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 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.