Cosmological Constrained Axion-Portal Inelastic Dark Matter for the LZ Event
Abstract
The recent high-recoil candidate event reported by LUX-ZEPLIN (LZ) motivates dark-matter scenarios with nonstandard kinematics and momentum-dependent interactions. We study a two-state inelastic dark-matter model in which χ1 and χ2 couple off-diagonally to an axion-like particle (ALP) that also couples to gluons and photons. Unlike treatments that assume only one dark-matter state is present today, we track the cosmological evolution of both states. The excited state χ2 is sufficiently long-lived to survive to the present, with its relic fraction determined by the dark-sector conversion process χ2χ2↔χ1χ1. We find that this fraction depends strongly on the Lorentz structure of the DM--ALP interaction: scalar transition couplings efficiently deplete χ2, favoring endothermic χ1 N→χ2 N scattering, whereas pseudoscalar transition couplings preserve f2≃1/2, yielding recoil spectra dominated by exothermic χ2 N→χ1 N down-scattering. Benchmark spectra in all four scenarios can peak near the observed recoil energy of 250 keV. Our results demonstrate that the dominant direction of inelastic scattering in direct detection can be dynamically selected by the early-Universe evolution of the dark sector. With additional data, annual modulation measurements could distinguish these scenarios. We further show that the ALP portal can be directly probed at colliders.
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BibTeX
@misc{an2026cosmological,
title = {{Cosmological Constrained Axion-Portal Inelastic Dark Matter for the LZ Event}},
author = {Haipeng An and Fei Gao and Jia Liu and Minghao Liu and Changlong Xu},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17412},
eprint = {2609.17412},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17412},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Cosmological Constrained Axion-Portal Inelastic Dark Matter for the LZ Event
AU - Haipeng An
AU - Fei Gao
AU - Jia Liu
AU - Minghao Liu
AU - Changlong Xu
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17412
UR - https://arxiv.org/abs/2609.17412
AB - The recent high-recoil candidate event reported by LUX-ZEPLIN (LZ) motivates dark-matter scenarios with nonstandard kinematics and momentum-dependent interactions. We study a two-state inelastic dark-matter model in which χ_1 and χ_2 couple off-diagonally to an axion-like particle (ALP) that also couples to gluons and photons. Unlike treatments that assume only one dark-matter state is present today, we track the cosmological evolution of both states. The excited state χ_2 is sufficiently long-lived to survive to the present, with its relic fraction determined by the dark-sector conversion process χ_2χ_2↔χ_1χ_1. We find that this fraction depends strongly on the Lorentz structure of the DM--ALP interaction: scalar transition couplings efficiently deplete χ_2, favoring endothermic χ_1 N→χ_2 N scattering, whereas pseudoscalar transition couplings preserve f_2≃1/2, yielding recoil spectra dominated by exothermic χ_2 N→χ_1 N down-scattering. Benchmark spectra in all four scenarios can peak near the observed recoil energy of 250 keV. Our results demonstrate that the dominant direction of inelastic scattering in direct detection can be dynamically selected by the early-Universe evolution of the dark sector. With additional data, annual modulation measurements could distinguish these scenarios. We further show that the ALP portal can be directly probed at colliders.
ER -