Exothermic Higgs portal: from LUX-ZEPLIN recoil to Gamma Rays
Abstract
We show that a minimal extension of the Standard Model (SM) by a single complex scalar ϕ provides a viable inelastic exothermic, thermal relic, interpretation of the recently reported nuclear-recoil candidate from LUX-ZEPLIN (LZ). The mass terms and Higgs-portal interactions split ϕ into two nearly degenerate real scalars, ϕ1,2. For mass-splitting of a few hundred keV, ϕ2 is cosmologically long-lived and the two states have comparable relic abundances. Taking ϕ1,2 masses to be ∼100GeV, with off-diagonal Higgs coupling fixed by relic abundance, the exothermic down-scattering yields an order-one event expectation for the LZ exposure, without relying on the high-velocity tail of the dark matter velocity distribution required in endothermic scenarios. This scenario can be tested using different nuclear targets and with indirect dark matter searches: ϕ2→ϕ1γγ decays give a broad sub-MeV photon continuum that can be probed by INTEGRAL/SPI and COSI; ϕ1ϕ2 annihilation produces a GeV-scale continuum, extending up to ∼100 GeV, that is probed by Fermi-LAT observations of dwarf galaxies; current CMB constraints are satisfied and annihilation among dark matter particles captured in the Sun is strongly suppressed. Next-generation experiments could probe correlated scattering, decay, and annihilation signatures of this thermal Higgs-portal scenario.
Related
- Inelastic Dark Photon Dark Matter for the LUX-ZEPLIN High-Recoil Event and the Galactic Halo Gamma-Ray Excess
- Higgsino Dark Matter Interpretation of the LUX-ZEPLIN 248 keV Nuclear-Recoil Event
- Sub-TeV Singlino Dark Matter in light from Sagittarius A∗ and LUX-ZEPLIN Nuclear-Recoil Event
- A Vector-Like Lepton Interpretation of the High-Energy Nuclear Recoil Candidate in LUX-ZEPLIN
- Interpreting the High-Recoil LUX-ZEPLIN Event with Bino-/Singlino-like and Higgsino Dark Matter
BibTeX
@misc{roy2026exothermic,
title = {{Exothermic Higgs portal: from LUX-ZEPLIN recoil to Gamma Rays}},
author = {Subhojit Roy and Jure Zupan},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.01158},
eprint = {2611.01158},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.01158},
note = {CC0},
}
RIS
TY - UNPB
TI - Exothermic Higgs portal: from LUX-ZEPLIN recoil to Gamma Rays
AU - Subhojit Roy
AU - Jure Zupan
PY - 2026
DA - 2026/11/01
PB - arXiv
DO - 10.48550/arxiv.2611.01158
UR - https://arxiv.org/abs/2611.01158
AB - We show that a minimal extension of the Standard Model (SM) by a single complex scalar ϕ provides a viable inelastic exothermic, thermal relic, interpretation of the recently reported nuclear-recoil candidate from LUX-ZEPLIN (LZ). The mass terms and Higgs-portal interactions split ϕ into two nearly degenerate real scalars, ϕ_1,2. For mass-splitting of a few hundred keV, ϕ_2 is cosmologically long-lived and the two states have comparable relic abundances. Taking ϕ_1,2 masses to be ∼100GeV, with off-diagonal Higgs coupling fixed by relic abundance, the exothermic down-scattering yields an order-one event expectation for the LZ exposure, without relying on the high-velocity tail of the dark matter velocity distribution required in endothermic scenarios. This scenario can be tested using different nuclear targets and with indirect dark matter searches: ϕ_2→ϕ_1γγ decays give a broad sub-MeV photon continuum that can be probed by INTEGRAL/SPI and COSI; ϕ_1ϕ_2 annihilation produces a GeV-scale continuum, extending up to ∼100 GeV, that is probed by Fermi-LAT observations of dwarf galaxies; current CMB constraints are satisfied and annihilation among dark matter particles captured in the Sun is strongly suppressed. Next-generation experiments could probe correlated scattering, decay, and annihilation signatures of this thermal Higgs-portal scenario.
ER -