A Simple Dark Matter Model to Explain the LZ Event and Galactic Center Excess
Abstract
We propose that the dark matter (DM) is a pseudo-Dirac fermion with a mass of approximately 20−100 GeV that couples inelastically to the Standard Model through a hadrophilic spin-1 mediator, V, the gauge boson of spontaneously broken baryon number. The two DM eigenstates, χ1 and χ2, acquire approximately equal abundances after thermal freeze-out and are depleted through the processes χ1 χ1 → VV and χ2 χ2 → VV. Although the heavier state is unstable, for a mass splitting below the electron-positron threshold and sufficiently small mass mixing with the Z boson, its lifetime can exceed the age of the universe, allowing both states to remain approximately equally abundant in the Galactic halo. For a thermal-relic annihilation cross section, this model can produce a signal that is consistent with the observed features of the longstanding Galactic Center Gamma-Ray Excess (GCE). If δ∼ 1000 keV, the same parameter space that explains the GCE can also explain the LZ event through exothermic χ2 → χ1 downscattering off xenon nuclei.
Related
- Comment on "Fermi-LAT Galactic Center Excess Morphology of Dark Matter in Simulations of the Milky Way Galaxy"
- Dark Matter Interpretations of the Galactic Center Gamma-Ray Excess with 18 Years of Fermi-LAT Data and the FL16Y Source Catalog
- Inelastic Dark Photon Dark Matter for the LUX-ZEPLIN High-Recoil Event and the Galactic Halo Gamma-Ray Excess
- The Galactic Center Gamma-Ray Excess and the Look-Elsewhere Effect
- First results on the search for the Galactic Center Excess in the sub-GeV band with the emulsion telescope in GRAINE 2023
BibTeX
@misc{gemmell2026simple,
title = {{A Simple Dark Matter Model to Explain the LZ Event and Galactic Center Excess}},
author = {Caleb Gemmell and Dan Hooper and Gordan Krnjaic},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.26570},
eprint = {2609.26570},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.26570},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - A Simple Dark Matter Model to Explain the LZ Event and Galactic Center Excess
AU - Caleb Gemmell
AU - Dan Hooper
AU - Gordan Krnjaic
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.26570
UR - https://arxiv.org/abs/2609.26570
AB - We propose that the dark matter (DM) is a pseudo-Dirac fermion with a mass of approximately 20−100 GeV that couples inelastically to the Standard Model through a hadrophilic spin-1 mediator, V, the gauge boson of spontaneously broken baryon number. The two DM eigenstates, χ_1 and χ_2, acquire approximately equal abundances after thermal freeze-out and are depleted through the processes χ_1 χ_1 → VV and χ_2 χ_2 → VV. Although the heavier state is unstable, for a mass splitting below the electron-positron threshold and sufficiently small mass mixing with the Z boson, its lifetime can exceed the age of the universe, allowing both states to remain approximately equally abundant in the Galactic halo. For a thermal-relic annihilation cross section, this model can produce a signal that is consistent with the observed features of the longstanding Galactic Center Gamma-Ray Excess (GCE). If δ∼ 1000 keV, the same parameter space that explains the GCE can also explain the LZ event through exothermic χ_2 → χ_1 downscattering off xenon nuclei.
ER -