Composition g-modes and f-modes of neutron stars with gravitationally coupled dark matter: degeneracy with the symmetry energy
Abstract
Composition gravity (g) modes have been proposed as a probe of dark matter in neutron stars, on the basis of one-fluid models in which the dark matter is in chemical equilibrium with the neutrons. We computed in full general relativity the g- and f-modes of stars in which fermionic dark matter couples to the nucleons only through gravity, and inferred the dark mass fraction from NICER and GW170817 data with a prior that comprises $63$ nucleonic equations of state (EOSs) from Skyrme and relativistic mean-field functionals, among them the models of Dutra \textit{et al.} and of the compilation of Sun, Bhattiprolu and Lattimer. The data do not prefer dark matter and bound its mass fraction at $0.12 - 0.26$ (95%) for particle masses of $0.5−−2$~GeV. Coupled only through gravity, the dark matter reaches the buoyancy that restores a g-mode only through the gravitational field: a dark core holding 10% of the mass raises the fundamental g-mode by 10−15% at fixed EOS, several times less than in the one-fluid picture. The larger effect is indirect: a star with a dark core needs a stiffer nucleonic EOS, and since the g-mode is set by the density dependence of the symmetry energy, its frequency reflects the EOS that the star requires rather than the dark matter it contains; at fixed radius and symmetry energy a core holding 10% of the mass is equivalent to a change of the slope L of 9−12~MeV. The f-mode, which follows the mean density, behaves differently: a dark core breaks the relation between the f-mode and the tidal deformability by about one percent, far outside the posterior spread of nucleonic stars.
Related
- Effects of the Symmetry energy slope on the exotic content of the neutron stars
- Higher-Order Symmetry Energy Effects on the Properties of Neutron Stars
- Symmetry energy effect on hot nuclear matter and proto-neutron stars
- Core Composition Effects on the QCD Axion Mass Limit from Neutron Star Cooling
- Breaking the symmetry: X-ray polarization from a spreading layer on a tilted weakly magnetized neutron star
BibTeX
@misc{kalita2026composition,
title = {{Composition $g$-modes and $f$-modes of neutron stars with gravitationally coupled dark matter: degeneracy with the symmetry energy}},
author = {Probit J Kalita and Bharat Kumar and H C Das},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10007},
eprint = {2610.10007},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10007},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Composition g-modes and f-modes of neutron stars with gravitationally coupled dark matter: degeneracy with the symmetry energy
AU - Probit J Kalita
AU - Bharat Kumar
AU - H C Das
PY - 2026
DA - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2610.10007
UR - https://arxiv.org/abs/2610.10007
AB - Composition gravity (g) modes have been proposed as a probe of dark matter in neutron stars, on the basis of one-fluid models in which the dark matter is in chemical equilibrium with the neutrons. We computed in full general relativity the g- and f-modes of stars in which fermionic dark matter couples to the nucleons only through gravity, and inferred the dark mass fraction from NICER and GW170817 data with a prior that comprises $63$ nucleonic equations of state (EOSs) from Skyrme and relativistic mean-field functionals, among them the models of Dutra \textit{et al.} and of the compilation of Sun, Bhattiprolu and Lattimer. The data do not prefer dark matter and bound its mass fraction at $0.12 - 0.26$ (95%) for particle masses of $0.5−−2$~GeV. Coupled only through gravity, the dark matter reaches the buoyancy that restores a g-mode only through the gravitational field: a dark core holding 10% of the mass raises the fundamental g-mode by 10−15% at fixed EOS, several times less than in the one-fluid picture. The larger effect is indirect: a star with a dark core needs a stiffer nucleonic EOS, and since the g-mode is set by the density dependence of the symmetry energy, its frequency reflects the EOS that the star requires rather than the dark matter it contains; at fixed radius and symmetry energy a core holding 10% of the mass is equivalent to a change of the slope L of 9−12~MeV. The f-mode, which follows the mean density, behaves differently: a dark core breaks the relation between the f-mode and the tidal deformability by about one percent, far outside the posterior spread of nucleonic stars.
ER -