Probing Strange Dark Matter through $f$-mode Oscillations of Neutron Stars with Hyperons and Quark Matter

TL;DR

This work investigates how a bosonic dark-matter candidate (the sexaquark) and exotic core constituents (hyperons and deconfined quark matter) modify neutron-star $f$-mode oscillations within fully general-relativistic hybrid EOSs that implement a smooth hadron–quark crossover. By varying the DM mass and coupling and confronting models with NICER and GW170817 constraints, the authors show that $f$-mode frequencies and damping times are sensitive to composition, with quasi-universal relations requiring higher-order fits to remain EOS-insensitive. They provide explicit polynomial forms for $f$ vs mean density, damping-time vs compactness, and $oldsymbol{b}$-mode frequency relations, demonstrating that DM and exotic matter can imprint measurable signatures in gravitational-wave signals. The results imply that next-generation GW detectors could use $f$-mode observations to probe dark matter properties and the presence of hyperons and quark matter in NS interiors.

Abstract

We investigate the impact of a hypothetical bosonic dark matter (DM) candidate, the sexaquark, on the fundamental ($f$-mode) oscillations of neutron stars (NSs). By varying the DM particle mass and considering different core compositions including hypernuclear matter, sexaquark DM, and deconfined quark matter (QM), we construct hybrid equations of state (EOS) with a smooth hadron--quark crossover that remain consistent with current astrophysical constraints on mass, radius, and tidal deformability. Our analysis shows that the presence of these exotic components systematically alters quasi-universal $f$-mode relations. In particular, relations involving $f$--$\sqrt{M/R^{3}}$, $(R^{4}/M^{3}τ)(C)$, $ωM(C)$, require higher-order polynomial fits compared to standard studies. Quadratic forms remain sufficient for $f$--$\sqrt{M/R^{3}}$ and $ωM(C)$, while damping-time relations such as $(R^{4}/M^{3}τ)(C)$ demand higher-order corrections to capture their curvature. For $f(Λ)$, a cubic fit provides a satisfactory description. Within this extended framework the relations remain tight and effectively composition independent. These results suggest that precise $f$-mode measurements with future gravitational-wave detectors could provide clear signatures of DM and other exotic matter in NS interiors.

Figures (13)

• Figure 1: Pressure as a function of energy density for all EOSs. Pure hadronic models with (DD2Y-T+S) and without (DD2 and DD2Y-T) DM, as well as hybrid models featuring a quark matter core (RIC-DD2Y-T and RIC-DD2Y-T+S), are shown. Various DM masses and two different values of the coupling parameter $x$ are used to explore different scenarios in this work. The constraints from Hebeler et al. Hebeler:2013nza and Miller et al. Miller:2021qha are represented by the gray region and the black dashed line, respectively.
• Figure 2: Mass-Radius profiles for three scenarios considered in this work. The left panel indicates the effect of different masses of S (DM) particles ($x=0.03$), the middle one shows the impacts of DM emergence on hybrid stars ($x=0.03$), while the right one depicts how each new degree of freedom affects the mass and radius of the object ($x=0.08$). The colored regions represent observational constraints from the NICER mass-radius measurements.
• Figure 3: Similar to Fig. \ref{['fig:M-R']}, but for the tidal deformability versus the mass of the object. The observational constraint from the LIGO–Virgo collaboration for a $1.4~M_\odot$ NS, derived from the GW170817 event, is indicated by a magenta line.
• Figure 4: Particle fractions as a function of radial distance from the center of the star for the first scenario.
• Figure 5: Particle fractions as a function of radial distance from the center of the star for the second scenario.