ALP-Mediated Dark Matter at Low Reheating Temperature and the Belle II Excess
Abstract
Belle II has reported a 2.7σ excess in B+→ K+νν̅ over its Standard Model prediction, recently interpreted as arising from an axion-like particle mediating a thermal dark matter candidate. We reassess this interpretation using a new mass-differential measurement of the same data set and adding two visible-decay searches that earlier analyses omitted. The resulting bounds leave the predictions from a standard cosmological history only marginally compatible with the excess, viable in a narrow window of parameter space. Thus, we consider a situation where dark matter freezes out during a low-temperature reheating era, featuring entropy injection diluting the relic abundance. This requires smaller couplings compared to those in standard cosmology in order to match the observed dark matter density, opening a region of parameter space where the compatibility of the model with the Belle II excess is significantly improved.
Related
- Probing dark-matter scenarios of Belle II excess in B+→ K+MX with K+→ π+ MX decays
- Dark photon portal dark matter with low-temperature reheating
- Freeze-in SU(2) vector dark matter at low reheating temperature
- B(s)→ V MX decays as probes of dark-matter scenarios of Belle II enhancement in B→ KMX decays
- FIMP dark matter in the scotogenic model at low-reheating temperatures
BibTeX
@misc{jonesperez2026alpmediated,
title = {{ALP-Mediated Dark Matter at Low Reheating Temperature and the Belle II Excess}},
author = {Joel Jones-Pérez and Luca Merlo and Javier Silva-Malpartida},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.00460},
eprint = {2610.00460},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.00460},
}
RIS
TY - UNPB
TI - ALP-Mediated Dark Matter at Low Reheating Temperature and the Belle II Excess
AU - Joel Jones-Pérez
AU - Luca Merlo
AU - Javier Silva-Malpartida
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2610.00460
UR - https://arxiv.org/abs/2610.00460
AB - Belle II has reported a 2.7σ excess in B^+→ K^+νν̅ over its Standard Model prediction, recently interpreted as arising from an axion-like particle mediating a thermal dark matter candidate. We reassess this interpretation using a new mass-differential measurement of the same data set and adding two visible-decay searches that earlier analyses omitted. The resulting bounds leave the predictions from a standard cosmological history only marginally compatible with the excess, viable in a narrow window of parameter space. Thus, we consider a situation where dark matter freezes out during a low-temperature reheating era, featuring entropy injection diluting the relic abundance. This requires smaller couplings compared to those in standard cosmology in order to match the observed dark matter density, opening a region of parameter space where the compatibility of the model with the Belle II excess is significantly improved.
ER -