Secular effects of Ultralight Dark Matter on Binary Pulsars

TL;DR

This paper investigates how ultralight dark matter could cause measurable secular changes in binary pulsar orbits, providing a new way to constrain dark matter properties through pulsar timing.

Contribution

It identifies two classes of orbital effects induced by ultralight dark matter and demonstrates how binary pulsar timing can be used to constrain dark matter couplings and masses.

Findings

Current pulsar timing constrains DM masses around 10^{-22} to 10^{-18} eV.

Resonant effects occur if DM oscillation frequency matches orbital frequency.

Quadratic coupling effects do not require resonance and are also constrained.

Abstract

Dark matter (DM) can consist of very light bosons behaving as a classical scalar field that experiences coherent oscillations. The presence of this DM field would perturb the dynamics of celestial bodies, either because the (oscillating) DM stress tensor modifies the gravitational potentials of the galaxy, or if DM is directly coupled to the constituents of the body. We study secular variations of the orbital parameters of binary systems induced by such perturbations. Two classes of effects are identified. Effects of the first class appear if the frequency of DM oscillations is in resonance with the orbital motion; these exist for general DM couplings including the case of purely gravitational interaction. Effects of the second class arise if DM is coupled quadratically to the masses of the binary system members and do not require any resonant condition. The exquisite precision of binary pulsar timing can be used to constrain these effects. Current observations are not sensitive to oscillations in the galactic gravitational field, though a discovery of pulsars in regions of high DM density may improve the situation. For DM with direct coupling to ordinary matter, the current timing data are already competitive with other existing constraints in the range of DM masses $\sim 10^{-22}-10^{-18}\,{\rm eV}$. Future observations are expected to increase the sensitivity and probe new regions of parameters.