Constraints on Symmetric Dark Matter from Neutron Star Capture and Collapse

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Main Authors: Liu, Yuxin, Liu, Zhen, Pospelov, Maxim, Reddy, Sanjay
Format: Preprint
Published: 2025
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author Liu, Yuxin
Liu, Zhen
Pospelov, Maxim
Reddy, Sanjay
author_facet Liu, Yuxin
Liu, Zhen
Pospelov, Maxim
Reddy, Sanjay
contents Dark matter (DM) models with a conserved particle$-$antiparticle number, $n_χ-n_{\tilde χ}$, and the asymmetry in the cosmological abundance $n_χ\neq n_{\tilde χ}$, 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, $n_χ= n_{\tilde χ}$, as the process of DM capture regulated by a nucleon-DM scattering can be inherently asymmetric, $σ_{χn}\neq σ_{\tildeχn}$. The asymmetry is induced by the interference of different types of $χ$-$n$ interactions, provided that their combination is odd under charge conjugation in the DM sector, $C_χ$, and even under combined parity $P_{χ+ n}$. We provide a complete analysis of DM-nucleon bilinear $χ$-$n$ 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 $σ_{nχ}\!\gtrsim\!10^{-46}\,{\rm cm}^{2}$ at DM mass $m_χ\!\lesssim\!10^{10}\,{\rm GeV}$ for the maximally asymmetric capture rate, and show that the constraints persist down to very small values of the cross-section asymmetry, ${\cal A}=(σ_{χn}- σ_{\tildeχn})/(σ_{χn}+ σ_{\tildeχn})\gtrsim 10^{-5}$.
format Preprint
id arxiv_https___arxiv_org_abs_2508_04961
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Constraints on Symmetric Dark Matter from Neutron Star Capture and Collapse
Liu, Yuxin
Liu, Zhen
Pospelov, Maxim
Reddy, Sanjay
High Energy Physics - Phenomenology
High Energy Astrophysical Phenomena
Dark matter (DM) models with a conserved particle$-$antiparticle number, $n_χ-n_{\tilde χ}$, and the asymmetry in the cosmological abundance $n_χ\neq n_{\tilde χ}$, 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, $n_χ= n_{\tilde χ}$, as the process of DM capture regulated by a nucleon-DM scattering can be inherently asymmetric, $σ_{χn}\neq σ_{\tildeχn}$. The asymmetry is induced by the interference of different types of $χ$-$n$ interactions, provided that their combination is odd under charge conjugation in the DM sector, $C_χ$, and even under combined parity $P_{χ+ n}$. We provide a complete analysis of DM-nucleon bilinear $χ$-$n$ 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 $σ_{nχ}\!\gtrsim\!10^{-46}\,{\rm cm}^{2}$ at DM mass $m_χ\!\lesssim\!10^{10}\,{\rm GeV}$ for the maximally asymmetric capture rate, and show that the constraints persist down to very small values of the cross-section asymmetry, ${\cal A}=(σ_{χn}- σ_{\tildeχn})/(σ_{χn}+ σ_{\tildeχn})\gtrsim 10^{-5}$.
title Constraints on Symmetric Dark Matter from Neutron Star Capture and Collapse
topic High Energy Physics - Phenomenology
High Energy Astrophysical Phenomena
url https://arxiv.org/abs/2508.04961