Kinetic Equilibrium between SIMP Dark Matter and Radiation via Internal Bremsstrahlung
Abstract
As an alternative to standard dark matter freeze-out via two-body annihilation, strongly interacting massive particles are proposed to regulate their relic abundance through three/four-body self-annihilation. During such freeze-out, dark matter must undergo both number reduction and energy dissipation. The former requires number-reducing processes, and the latter requires an efficient energy-dissipation mechanism. In this work, we propose a novel mechanism where internal Bremsstrahlung processes establish kinetic equilibrium between dark matter and radiation, and thus dissipate energy. More appealingly, this mechanism can be naturally realized in a class of strong dynamics models with flavor-universal quarks and a light axion. To demonstrate our results in a Sp(4)c dark-color model, we compute all relevant interaction terms and numerically solve the full Boltzmann equations. The same mechanism can also be applied to vector dark matter models.
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BibTeX
@misc{chu2026kinetic,
title = {{Kinetic Equilibrium between SIMP Dark Matter and Radiation via Internal Bremsstrahlung}},
author = {Xiaoyong Chu and Ajay Kaladharan and Yassine El Mohtadi},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.02820},
eprint = {2610.02820},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.02820},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Kinetic Equilibrium between SIMP Dark Matter and Radiation via Internal Bremsstrahlung
AU - Xiaoyong Chu
AU - Ajay Kaladharan
AU - Yassine El Mohtadi
PY - 2026
DA - 2026/10/02
PB - arXiv
DO - 10.48550/arxiv.2610.02820
UR - https://arxiv.org/abs/2610.02820
AB - As an alternative to standard dark matter freeze-out via two-body annihilation, strongly interacting massive particles are proposed to regulate their relic abundance through three/four-body self-annihilation. During such freeze-out, dark matter must undergo both number reduction and energy dissipation. The former requires number-reducing processes, and the latter requires an efficient energy-dissipation mechanism. In this work, we propose a novel mechanism where internal Bremsstrahlung processes establish kinetic equilibrium between dark matter and radiation, and thus dissipate energy. More appealingly, this mechanism can be naturally realized in a class of strong dynamics models with flavor-universal quarks and a light axion. To demonstrate our results in a Sp(4)_c dark-color model, we compute all relevant interaction terms and numerically solve the full Boltzmann equations. The same mechanism can also be applied to vector dark matter models.
ER -