{
  "abstract": "An excited dark-matter state can produce a high-energy nuclear recoil by releasing its mass splitting in a collision. Motivated by the $248$~keV LUX--ZEPLIN candidate, we study freeze-in of a $45$~GeV pseudo-Dirac particle with a $1$~MeV splitting and a $1$~GeV dark photon during non-instantaneous reheating. We choose a recoil normalization compatible with the published INTEGRAL/SPI three-photon decay limit. It predicts $0.43$ events in the LZ window and retains the reference recoil shape. Including both dark-photon and $Z$ exchange, we calculate production and entropy dilution for backgrounds with $T\\propto a^{-α}$ and $ρ_ϕ\\propto a^{-3(1+ω)}$. For $\\Tmax=m_χ$, the observed abundance requires $\\Trh=1.32$~GeV for matter-like constant-width reheating, $3.09$~GeV for quartic oscillations with scalar decay, and $0.588$~GeV for quartic oscillations with constant width, compared with $4.10$~GeV for instantaneous reheating. These finite-reheating solutions are insensitive to increasing $\\Tmax$ above $m_χ$. For $\\Tmax\\geq m_χ$, adiabatic kination has no solution with $\\Trh>5.96$~MeV, the BBN-motivated cutoff adopted for our scans. At $α_D=10^{-10}$, the estimated thermal-mediator source is below $0.2\\%$ of the Standard Model source, and self-conversion does not appreciably deplete the excited population. The calculation relates an exothermic recoil benchmark to the production and dilution history before radiation domination.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.18974",
  "author_total": 1,
  "authors": [
    {
      "name": "Kuldeep Deka"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/0ep02ph4qre1a.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.18974",
  "fulltext_url": null,
  "id": "0ep02ph4qre1a",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.18974",
  "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": "W7221887607",
  "pdf_url": "https://arxiv.org/pdf/2610.18974",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-13",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/0ep02ph4qre1a.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:29:31Z",
      "native_id": "2610.18974",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.18974"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-ph",
      "subfield": "high-energy"
    }
  ],
  "title": "Exothermic dark-photon dark matter and the LZ high-recoil event: finite-reheating constraints",
  "title_text": "Exothermic dark-photon dark matter and the LZ high-recoil event: finite-reheating constraints",
  "type": "preprint",
  "updated_at": "2026-10-30T12:29:31Z",
  "url": "https://research.draconitic.com/paper/0ep02ph4qre1a",
  "venue": "arXiv",
  "versions": []
}