Testing scalar dark matter clumps with Pulsar Timing Arrays

TL;DR

This paper explores how Pulsar Timing Arrays can detect ultralight scalar dark matter by measuring pulsar signal delays, extending current mass sensitivity, but faces challenges due to low capture rates and the need for specific astrophysical conditions.

Contribution

It proposes a novel method using synchronized pulsar timing to probe higher mass ranges of ultralight dark matter than previous analyses.

Findings

PTA can probe scalar dark matter masses from 10^{-23} to 10^{-19} eV.

Detection sensitivity depends on the observation time lag between pulsar measurements.

High-density dark matter clouds are required for detection at higher scalar masses.

Abstract

Scalar dark matter is a viable alternative to particle dark matter models such as Weakly Interacting Massive Particles (WIMPS). This is particularly the case for scalars with a low mass $m \gtrsim 10^{-21} {\rm eV}$ as required to make quantum effects macroscopic on galactic scales. We point out that by synchronising the measurements of arrival times of pairs of pulsars, Pulsar Timing Arrays (PTA) could probe ultralight dark matter (ULDM) scenarios with a mass $10^{-23} {\rm eV}\lesssim m \lesssim 10^{-19} {\rm eV}$ that is greater than the one reached in standard analysis. The upper limit on the mass $m$ is set by the time lag $\Delta t$ between the observations of the two pulsars and could be pushed above $10^{-19} {\rm eV}$ for $\Delta t$ smaller than one hour. However, for these high scalar masses only very high density dark matter clouds could be detected and the capture rate of neutron stars is too low to provide sufficient statistics. Significant detection probabilities would thus require direct dark-matter-baryon interactions that favor the formation of neutron stars within such dark matter clouds, or the discovery of black hole/pulsar binary systems, taking advantage of the dark matter spike generated by the black hole.