Ultra-relativistic freeze-out of fermion dark matter through a heavy scalar mediator
Abstract
We investigate the production of Majorana fermion dark matter (DM) via a heavy scalar mediator during reheating, with particular emphasis on ultra-relativistic freeze-out (UFO). Depending on the mediator mass, interaction strengths, and reheating temperature, we identify three distinct production regimes: freeze-in, WIMP-like freeze-out, and UFO, all of which can account for the observed DM relic abundance. In the UFO regime, significant DM production can persist after chemical decoupling, while entropy injection during reheating simultaneously dilutes the DM yield. An accurate determination of the final relic abundance therefore requires a consistent treatment of both continued production and entropy dilution. We further examine the impact of scalar cubic interactions and find that they modify the boundaries between the different production regimes and reshape the relic-density contours. In particular, the results are more sensitive to the cubic coupling involving the mediator and the light scalar than to the heavy-scalar self-coupling.
Related
- Relativistic Elastic Scattering of Cosmic-Ray Boosted Dirac Dark Matter with Charged Leptons through a Scalar Mediator
- Elastic Scattering of Dirac Dark Matter with Charged Leptons through a Scalar Mediator: Analytical Framework, Numerical Stability, and Direct-Detection Bounds
- Vacuum Polarization Effects from Dark Fermion Loops in Z' Mediator Models and their Impact on Angular Observables in B → K* μ+μ- Decays
- Effective Fermion-Photon Vertex in a Rotating Relativistic Medium: Tree-Level Structure
- Kaon Portal to Freeze-in Dark Matter
BibTeX
@misc{yang2026ultrarelativistic,
title = {{Ultra-relativistic freeze-out of fermion dark matter through a heavy scalar mediator}},
author = {Jin-Lei Yang and Ke-Shuo Cai and Yin-Jie Zhang and Hai-Bin Zhang and Tai-Fu Feng},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.24547},
eprint = {2610.24547},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.24547},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Ultra-relativistic freeze-out of fermion dark matter through a heavy scalar mediator
AU - Jin-Lei Yang
AU - Ke-Shuo Cai
AU - Yin-Jie Zhang
AU - Hai-Bin Zhang
AU - Tai-Fu Feng
PY - 2026
DA - 2026/10/17
PB - arXiv
DO - 10.48550/arxiv.2610.24547
UR - https://arxiv.org/abs/2610.24547
AB - We investigate the production of Majorana fermion dark matter (DM) via a heavy scalar mediator during reheating, with particular emphasis on ultra-relativistic freeze-out (UFO). Depending on the mediator mass, interaction strengths, and reheating temperature, we identify three distinct production regimes: freeze-in, WIMP-like freeze-out, and UFO, all of which can account for the observed DM relic abundance. In the UFO regime, significant DM production can persist after chemical decoupling, while entropy injection during reheating simultaneously dilutes the DM yield. An accurate determination of the final relic abundance therefore requires a consistent treatment of both continued production and entropy dilution. We further examine the impact of scalar cubic interactions and find that they modify the boundaries between the different production regimes and reshape the relic-density contours. In particular, the results are more sensitive to the cubic coupling involving the mediator and the light scalar than to the heavy-scalar self-coupling.
ER -