Neutron-star dark-matter limits measure the maximum-mass headroom
Abstract
Neutron stars constrain dark matter that is present inside them, through their maximum mass and the tidal deformability. The standard approach adds a dark component to one nuclear equation of state (EoS) and compares the stars with pulsar masses and with GW170817, so each limit inherits an EoS dependence that has not been quantified. In this paper we add a QCD axion and a Z'-portal dark fermion to the relativistic mean-field (RMF) model, in the formulation of the public code of Kumamoto et al.\ [Phys.\ Rev.\ D \textbf{112}, 043008 (2025)], and compute the stars for $257$ published RMF parameter sets from the compilation of Sun, Bhattiprolu, and Lattimer [Phys.\ Rev.\ C \textbf{109}, 055801 (2024)], with the dark matter either moving with the baryons or in its own equilibrium. We find that the stars constrain only the dark rest mass per baryon, and that its upper limit is the maximum-mass headroom of the EoS above the pulsar-mass bound divided by a quasi-universal rate, whose residual follows the compactness of the maximum-mass star; a compact dark core roughly doubles the rate, and the axion condensate barely changes it. Capture cannot supply the dark matter the stars could detect, and the portal reaches the EoS only at couplings disfavoured by anomaly cancellation, so a neutron-star limit on dark matter is a statement about the headroom of the nuclear EoS.
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BibTeX
@misc{kalita2026neutronstar,
title = {{Neutron-star dark-matter limits measure the maximum-mass headroom}},
author = {Probit J Kalita and Soham Singh and Pinku Routaray and Bharat Kumar},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.25240},
eprint = {2610.25240},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.25240},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Neutron-star dark-matter limits measure the maximum-mass headroom
AU - Probit J Kalita
AU - Soham Singh
AU - Pinku Routaray
AU - Bharat Kumar
PY - 2026
DA - 2026/10/18
PB - arXiv
DO - 10.48550/arxiv.2610.25240
UR - https://arxiv.org/abs/2610.25240
AB - Neutron stars constrain dark matter that is present inside them, through their maximum mass and the tidal deformability. The standard approach adds a dark component to one nuclear equation of state (EoS) and compares the stars with pulsar masses and with GW170817, so each limit inherits an EoS dependence that has not been quantified. In this paper we add a QCD axion and a Z'-portal dark fermion to the relativistic mean-field (RMF) model, in the formulation of the public code of Kumamoto et al.\ [Phys.\ Rev.\ D \textbf{112}, 043008 (2025)], and compute the stars for $257$ published RMF parameter sets from the compilation of Sun, Bhattiprolu, and Lattimer [Phys.\ Rev.\ C \textbf{109}, 055801 (2024)], with the dark matter either moving with the baryons or in its own equilibrium. We find that the stars constrain only the dark rest mass per baryon, and that its upper limit is the maximum-mass headroom of the EoS above the pulsar-mass bound divided by a quasi-universal rate, whose residual follows the compactness of the maximum-mass star; a compact dark core roughly doubles the rate, and the axion condensate barely changes it. Capture cannot supply the dark matter the stars could detect, and the portal reaches the EoS only at couplings disfavoured by anomaly cancellation, so a neutron-star limit on dark matter is a statement about the headroom of the nuclear EoS.
ER -