{
  "abstract": "The LUX-ZEPLIN (LZ) experiment has reported a single nuclear-recoil candidate at $248\\pm23\\,(\\mathrm{stat})\\pm23\\,(\\mathrm{sys})$ keV. We suggest that it comes from a GeV-scale dark state $χ_1$ that downscatters exothermically, $χ_1A\\toχ_2A$, and is continuously replenished in the halo by the slow decay $χ_0\\toχ_1χ_1$ of a long-lived parent. Because the recoil energy is supplied by the mass splitting rather than by the halo velocity, the event is a narrow line with no low-energy tail. Kinematics requires $m_{χ_1}\\gtrsim247$ MeV and fixes the splitting for each $m_{χ_1}$. The same line should appear at 700$-$810 keV in argon for $m_{χ_1}=0.3-10$ GeV. Normalizing to one LZ event also fixes the local rate of the radiative decay $χ_1\\toχ_2γγ$, up to the mediator's photon coupling. A rough $γ$-ray estimate then requires this coupling to be $\\lesssim10^{-2}$ of a proton-loop reference at $m_{χ_1}=10$ GeV, but $\\lesssim10^{-9}$ at 0.3 GeV, which favours daughters near 10 GeV.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.37561",
  "author_total": 3,
  "authors": [
    {
      "name": "Yongsoo Jho"
    },
    {
      "name": "Sanghwan Kim"
    },
    {
      "name": "Seong Chan Park"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/6f19337y3f98r.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.37561",
  "fulltext_url": null,
  "id": "6f19337y3f98r",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.37561",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "hep-ph"
    ],
    [
      "openalex",
      "3106|Dark Matter and Cosmic Phenomena"
    ]
  ],
  "openalex": "W7214994032",
  "pdf_url": "https://arxiv.org/pdf/2609.37561",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-29",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6f19337y3f98r.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:25:31Z",
      "native_id": "2609.37561",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.37561"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-ph",
      "subfield": "high-energy"
    }
  ],
  "title": "Decaying Dark Matter for the Exothermic Recoil at LZ",
  "title_text": "Decaying Dark Matter for the Exothermic Recoil at LZ",
  "type": "preprint",
  "updated_at": "2026-10-30T12:25:31Z",
  "url": "https://research.draconitic.com/paper/6f19337y3f98r",
  "venue": "arXiv",
  "versions": []
}