Constraints on Symmetric Dark Matter from Neutron Star Capture and Collapse

TL;DR

This paper explores how neutron star observations constrain symmetric and asymmetric dark matter models through capture and collapse mechanisms, extending previous limits to a wider class of interactions and asymmetries.

Contribution

It demonstrates that neutron star constraints apply broadly to symmetric dark matter models by analyzing asymmetric capture processes induced by interference effects.

Findings

Constraints exclude spin-averaged cross sections down to 10^{-46} cm^2 for DM mass up to 10^{10} GeV.

Asymmetry in DM-nucleon interactions can be very small, with constraints valid for asymmetry parameters as low as 10^{-5}.

The analysis covers a wide range of interaction types and asymmetries, expanding the applicability of neutron star constraints.

Abstract

Dark matter (DM) models with a conserved particle$-$antiparticle number, $n_\chi-n_{\tilde \chi}$, and the asymmetry in the cosmological abundance $n_\chi\neq n_{\tilde \chi}$, are known to be challenged by the existence of old neutron stars (NSs), as the sufficient accumulation of DM will lead to the collapse of NSs into black holes. We demonstrate that the applicability of these constraints is much wider and covers models with symmetric populations of DM, $n_\chi = n_{\tilde \chi}$, as the process of DM capture regulated by a nucleon-DM scattering can be inherently asymmetric, $\sigma_{\chi n}\neq \sigma_{\tilde\chi n}$. The asymmetry is induced by the interference of different types of $\chi$-$n$ interactions, provided that their combination is odd under charge conjugation in the DM sector, $C_\chi$, and even under combined parity $P_{\chi + n}$. We provide a complete analysis of DM-nucleon bilinear $\chi$-$n$ interactions and find that this asymmetry is very generic. Using canonical NS parameters and local DM halo inputs, we exclude spin-averaged scattering cross sections down to $\sigma_{n\chi}\!\gtrsim\!10^{-46}\,{\rm cm}^{2}$ at DM mass $m_\chi\!\lesssim\!10^{10}\,{\rm GeV}$ for the maximally asymmetric capture rate, and show that the constraints persist down to very small values of the cross-section asymmetry, ${\cal A}=(\sigma_{\chi n}- \sigma_{\tilde\chi n})/(\sigma_{\chi n}+ \sigma_{\tilde\chi n})\gtrsim 10^{-5}$.