Relativistic capture of dark matter by electrons in neutron stars

TL;DR

This paper develops a relativistic formalism to calculate dark matter capture by electrons in neutron stars, revealing significantly higher capture probabilities than nonrelativistic estimates, and highlighting neutron stars as promising dark matter detectors.

Contribution

It introduces a Lorentz invariant approach for relativistic dark matter-electron scattering, accounting for Pauli exclusion, and shows enhanced capture probabilities in neutron stars.

Findings

Capture probability can be five orders of magnitude larger than nonrelativistic estimates.

Neutron star heating can surpass terrestrial detection sensitivity for certain dark matter masses.

Characteristic features in sensitivity regions reveal interplay between kinematics and Pauli blocking.

Abstract

Dark matter can capture in neutron stars and heat them to observable luminosities. We study relativistic scattering of dark matter on highly degenerate electrons. We develop a Lorentz invariant formalism to calculate the capture probability of dark matter that accounts for the relativistic motion of the target particles and Pauli exclusion principle. We find that the actual capture probability can be five orders of magnitude larger than the one estimated using a nonrelativistic approach. For dark matter masses $10~{\rm eV}\textup{--}10~{\rm PeV}$, neutron star heating complements and can be more sensitive than terrestrial direct detection searches. The projected sensitivity regions exhibit characteristic features that demonstrate a rich interplay between kinematics and Pauli blocking of the DM--electron system. Our results show that old neutron stars could be the most promising target for discovering leptophilic dark matter.