Plasma Effects Suppress Mixing-Induced Collisional Freeze-In
Abstract
Dark matter that is weakly mixed with particles in a thermal plasma can be produced through both, oscillatory and collisional freeze-in. While plasma effects have long been known to suppress the former, their role in collisional freeze-in remains less clear quantitatively, leading to conflicting results in sterile neutrino dark matter production via collisional freeze-in. Using first-principles nonequilibrium Kadanoff-Baym equations in the flavour-covariant formulation, we establish the general result that plasma effects also suppress collisional freeze-in: the vacuum mixing angle in the collision rate is replaced by its plasma-corrected counterpart. Applying this result, we conclude that sterile neutrinos cannot be dark matter in the keV-MeV mass range when produced from the Standard Model plasma.
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BibTeX
@misc{li2026plasma,
title = {{Plasma Effects Suppress Mixing-Induced Collisional Freeze-In}},
author = {Shao-Ping Li and Josef Pradler},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.29911},
eprint = {2609.29911},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.29911},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Plasma Effects Suppress Mixing-Induced Collisional Freeze-In
AU - Shao-Ping Li
AU - Josef Pradler
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.29911
UR - https://arxiv.org/abs/2609.29911
AB - Dark matter that is weakly mixed with particles in a thermal plasma can be produced through both, oscillatory and collisional freeze-in. While plasma effects have long been known to suppress the former, their role in collisional freeze-in remains less clear quantitatively, leading to conflicting results in sterile neutrino dark matter production via collisional freeze-in. Using first-principles nonequilibrium Kadanoff-Baym equations in the flavour-covariant formulation, we establish the general result that plasma effects also suppress collisional freeze-in: the vacuum mixing angle in the collision rate is replaced by its plasma-corrected counterpart. Applying this result, we conclude that sterile neutrinos cannot be dark matter in the keV-MeV mass range when produced from the Standard Model plasma.
ER -