Asymmetric Inelastic Dark Matter and the LUX-ZEPLIN event
- 1Department of Physics , University of Tokyo , Bunkyo-ku , Tokyo 113-0033 , Japan
- 2Kavli Institute for the Physics and Mathematics of the Universe (WPI) , UTIAS , The University of Tokyo , Chiba 277-8583 , Japan
- 3Tsung-Dao Lee Institute & School of Physics and Astronomy , Shanghai Jiao Tong University , Pudong New Area , Shanghai 201210 , China
Abstract
The recent LUX-ZEPLIN (LZ) search at high nuclear-recoil energies reported an intriguing candidate event near 250 keV, motivating interpretations in terms of inelastic dark matter. A simple realization with Higgsino dark matter, however, is strongly constrained by capture and subsequent annihilation in the Sun, which would produce a high-energy neutrino flux excluded by IceCube. We propose an asymmetric inelastic dark-matter scenario that naturally avoids this tension. The dark matter is a predominantly Standard-Model-singlet Dirac fermion that mixes weakly with a nearly degenerate electroweak doublet. Its primordial asymmetry is generated by CP-violating out-of-equilibrium decays of heavy Majorana fermions produced nonthermally from inflaton decays, while the symmetric component is efficiently depleted through dark-sector interactions. The absence of an appreciable antiparticle abundance then suppresses dark-matter annihilation in the Sun and eliminates the associated IceCube constraint. The singlet-doublet structure simultaneously yields an off-diagonal Z-boson coupling proportional to the mixing angle, whereas the diagonal coupling is suppressed by its square. Consequently, an observable inelastic scattering rate can coexist with stringent limits on elastic scattering. We find that the LZ event can be accommodated for dark-matter masses of a few hundred GeV to 1 TeV, with mass splittings of a few hundred keV and mixing angles below O(10−2). Since the relic abundance is set by the primordial asymmetry rather than thermal freeze-out, lighter dark matter is also viable and can alleviate the potential tension with the absence of events in the LZ high-energy sideband. This framework predicts correlated elastic and inelastic direct-detection signals, together with complementary signatures at collider and precision experiments.
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BibTeX
@misc{nagata2026asymmetric,
title = {{Asymmetric Inelastic Dark Matter and the LUX-ZEPLIN event}},
author = {Natsumi Nagata and Tsutomu T. Yanagida},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18564},
eprint = {2609.18564},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18564},
}
RIS
TY - UNPB
TI - Asymmetric Inelastic Dark Matter and the LUX-ZEPLIN event
AU - Natsumi Nagata
AU - Tsutomu T. Yanagida
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.18564
UR - https://arxiv.org/abs/2609.18564
AB - The recent LUX-ZEPLIN (LZ) search at high nuclear-recoil energies reported an intriguing candidate event near 250 keV, motivating interpretations in terms of inelastic dark matter. A simple realization with Higgsino dark matter, however, is strongly constrained by capture and subsequent annihilation in the Sun, which would produce a high-energy neutrino flux excluded by IceCube. We propose an asymmetric inelastic dark-matter scenario that naturally avoids this tension. The dark matter is a predominantly Standard-Model-singlet Dirac fermion that mixes weakly with a nearly degenerate electroweak doublet. Its primordial asymmetry is generated by CP-violating out-of-equilibrium decays of heavy Majorana fermions produced nonthermally from inflaton decays, while the symmetric component is efficiently depleted through dark-sector interactions. The absence of an appreciable antiparticle abundance then suppresses dark-matter annihilation in the Sun and eliminates the associated IceCube constraint. The singlet-doublet structure simultaneously yields an off-diagonal Z-boson coupling proportional to the mixing angle, whereas the diagonal coupling is suppressed by its square. Consequently, an observable inelastic scattering rate can coexist with stringent limits on elastic scattering. We find that the LZ event can be accommodated for dark-matter masses of a few hundred GeV to 1 TeV, with mass splittings of a few hundred keV and mixing angles below O(10^−2). Since the relic abundance is set by the primordial asymmetry rather than thermal freeze-out, lighter dark matter is also viable and can alleviate the potential tension with the absence of events in the LZ high-energy sideband. This framework predicts correlated elastic and inelastic direct-detection signals, together with complementary signatures at collider and precision experiments.
SN - 2331-8422
ER -