Radii and Scaling Relations of Dark-Matter-Admixed Neutron Stars
Abstract
The radius of a neutron star is closely related to the equation of state (EOS) of asymmetric nuclear matter, particularly to the nuclear symmetry energy. At fixed stellar mass, the neutron-star radius and the nuclear-matter pressure near saturation density approximately satisfy a pressure--radius (R-P) scaling relation, linking stellar geometry to strong-interaction matter. In the presence of dark matter (DM), changes in the stellar geometry can modify this relation. We investigate how GeV- and sub-GeV-scale DM affects the R-P relation in DM-admixed neutron stars (DANSs) within a gravity-only two-fluid framework. We extend the Buchdahl analytic solution to a two-fluid configuration to demonstrate this scaling and then use 21 nuclear EOSs to fit the relation RNM=C̅ PNMη for 1M⊙ and 1.4M⊙ DANSs. The exponent η and coefficient C̅ jointly quantify the DM-induced modification and depend on the DM particle mass, stellar DM content, and self-interaction strength. For bosonic DM, changes in η and C̅ occur mainly in the sub-GeV range, whereas significant fermionic-DM effects persist up to about 1.5 GeV. Increasing the DM content or strengthening a repulsive self-interaction generally increases η and decreases C̅. The modified R-P relation therefore encodes information about the DM particle mass, abundance, and self-interaction, and affect the extraction of the nuclear EOS from celestial observations. At DM masses of several hundred MeV, both fermionic and bosonic DM can also produce DM-dominated low-mass (1M⊙) DANSs with large radial extensions, for which the conventional scaling relation ceases to apply.
Related
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BibTeX
@misc{li2026radii,
title = {{Radii and Scaling Relations of Dark-Matter-Admixed Neutron Stars}},
author = {Zhi-yao Li and Wei-zhou Jiang and Dian Sun},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.06934},
eprint = {2610.06934},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.06934},
}
RIS
TY - UNPB
TI - Radii and Scaling Relations of Dark-Matter-Admixed Neutron Stars
AU - Zhi-yao Li
AU - Wei-zhou Jiang
AU - Dian Sun
PY - 2026
DA - 2026/10/03
PB - arXiv
DO - 10.48550/arxiv.2610.06934
UR - https://arxiv.org/abs/2610.06934
AB - The radius of a neutron star is closely related to the equation of state (EOS) of asymmetric nuclear matter, particularly to the nuclear symmetry energy. At fixed stellar mass, the neutron-star radius and the nuclear-matter pressure near saturation density approximately satisfy a pressure--radius (R-P) scaling relation, linking stellar geometry to strong-interaction matter. In the presence of dark matter (DM), changes in the stellar geometry can modify this relation. We investigate how GeV- and sub-GeV-scale DM affects the R-P relation in DM-admixed neutron stars (DANSs) within a gravity-only two-fluid framework. We extend the Buchdahl analytic solution to a two-fluid configuration to demonstrate this scaling and then use 21 nuclear EOSs to fit the relation R_NM=C̅ P_NM^η for 1M_⊙ and 1.4M_⊙ DANSs. The exponent η and coefficient C̅ jointly quantify the DM-induced modification and depend on the DM particle mass, stellar DM content, and self-interaction strength. For bosonic DM, changes in η and C̅ occur mainly in the sub-GeV range, whereas significant fermionic-DM effects persist up to about 1.5 GeV. Increasing the DM content or strengthening a repulsive self-interaction generally increases η and decreases C̅. The modified R-P relation therefore encodes information about the DM particle mass, abundance, and self-interaction, and affect the extraction of the nuclear EOS from celestial observations. At DM masses of several hundred MeV, both fermionic and bosonic DM can also produce DM-dominated low-mass (1M_⊙) DANSs with large radial extensions, for which the conventional scaling relation ceases to apply.
ER -