Implications of Inelastic Dark Matter for Primordial Dark-Star Evolution: Kinematic Thresholds and Nonthermal Capture
Abstract
The recent 248-keV nuclear recoil candidate reported by LUX-ZEPLIN has renewed interest in endothermic inelastic dark matter, motivating us to examine its capture in primordial dark stars. Relative to the conventional elastic-capture picture in dark star evolution, endothermic capture adds two qualitative features. First, it opens only after the growing star crosses a compactness threshold, expressed as a kinematic radius Rkin∝μχM⋆/δ set by the stellar mass, the dark-matter--nucleus reduced mass and the mass splitting. The accreting growth carries the star through the threshold, and the capture rate turns on quadratically above it. Second, although newly captured particles generically begin on nonthermal bound orbits, endothermic kinematics can keep this normally transient population spatially extended, turning it into a persistent reservoir rather than an intermediate step toward a thermal core. Following complete chains of state-changing collisions, we find that the reservoir compacts sharply and then stalls, because a ground state particle below a compactness-dependent orbital energy has no allowed up-scatter anywhere in the star. A percent-level radius contraction reopens the relaxation. These kinematic results do not depend on whether the excited state decays promptly or is long-lived. As a result, inelastic capture does not replenish a thermal annihilation core. The captured population forms an evolving orbital distribution that sets up the co-evolutionary dynamics between the star and the dark matter in the core and the reservoir, which we develop in a companion paper.
Related
- Evolution of Jeans instability in nonthermal magnetized complex plasmas
- Search for subsolar primordial black holes in low mass-ratio binaries with LIGO-Virgo O2 data and implications for the primordial black hole dark matter fraction
- Isochrones in primordial magnetic field evolution
- An Open Cluster Origin for Most Solar-Type Binaries in the Solar Neighborhood and Implications for Primordial Planet Stability
- An Open Cluster Origin for Most Solar-type Binaries in the Solar Neighborhood and Implications for Primordial Planet Stability
BibTeX
@misc{li2026implications,
title = {{Implications of Inelastic Dark Matter for Primordial Dark-Star Evolution: Kinematic Thresholds and Nonthermal Capture}},
author = {Qinxun Li and Shengyi Liu},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.10662},
eprint = {2609.10662},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.10662},
}
RIS
TY - UNPB
TI - Implications of Inelastic Dark Matter for Primordial Dark-Star Evolution: Kinematic Thresholds and Nonthermal Capture
AU - Qinxun Li
AU - Shengyi Liu
PY - 2026
DA - 2026/09/09
PB - arXiv
DO - 10.48550/arxiv.2609.10662
UR - https://arxiv.org/abs/2609.10662
AB - The recent 248-keV nuclear recoil candidate reported by LUX-ZEPLIN has renewed interest in endothermic inelastic dark matter, motivating us to examine its capture in primordial dark stars. Relative to the conventional elastic-capture picture in dark star evolution, endothermic capture adds two qualitative features. First, it opens only after the growing star crosses a compactness threshold, expressed as a kinematic radius R_kin∝μ_χM_⋆/δ set by the stellar mass, the dark-matter--nucleus reduced mass and the mass splitting. The accreting growth carries the star through the threshold, and the capture rate turns on quadratically above it. Second, although newly captured particles generically begin on nonthermal bound orbits, endothermic kinematics can keep this normally transient population spatially extended, turning it into a persistent reservoir rather than an intermediate step toward a thermal core. Following complete chains of state-changing collisions, we find that the reservoir compacts sharply and then stalls, because a ground state particle below a compactness-dependent orbital energy has no allowed up-scatter anywhere in the star. A percent-level radius contraction reopens the relaxation. These kinematic results do not depend on whether the excited state decays promptly or is long-lived. As a result, inelastic capture does not replenish a thermal annihilation core. The captured population forms an evolving orbital distribution that sets up the co-evolutionary dynamics between the star and the dark matter in the core and the reservoir, which we develop in a companion paper.
ER -