{
  "abstract": "We present a joint multi-period analysis of axion-like particles (ALPs) using five sets of simultaneous Fermi-LAT and LHAASO observations of the TeV blazar Mrk~421. Photon-ALP oscillations are calculated self-consistently together with EBL absorption for two representative jet emission models: a two-zone hybrid model and a single-zone hadronic model. To account for weak correlations among different observational epochs, we adopt a $χ^2$-based profile analysis combined with a Gaussian copula ($ρ=0.03$). Nuisance parameters are optimized under the no-ALP hypothesis before profiling the ALP parameters $m_a$ and $g_{aγ}$. In the low-mass regime ($m_a\\lesssim1$\\,neV) we obtain a 95\\% CL upper limit of $g_{aγ}=6.35\\times10^{-13}\\,\\mathrm{GeV}^{-1}$. Over the full mass range $0.1$--$500$\\,neV, the most conservative 95\\% CL upper limits are $g_{aγ}<6.69\\times10^{-12}\\,\\mathrm{GeV}^{-1}$ (two-zone) and $g_{aγ}<7.37\\times10^{-12}\\,\\mathrm{GeV}^{-1}$ (single-zone). Variations of the EBL template, the Galactic and intergalactic magnetic-field models, the spectral binning, and residual instrumental systematics change these limits by only a few percent. The jet magnetic field is the leading systematic and can shift the low-mass bound by a factor of a few; only a substantially weaker single-zone field degrades the constraint by about an order of magnitude. The analysis framework developed here provides a statistically consistent approach for future ALP searches with multi-messenger gamma-ray data.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2606.05738",
  "author_total": 12,
  "authors": [
    {
      "name": "Longhua Qin"
    },
    {
      "name": "Jiancheng Wang"
    },
    {
      "name": "Chuyuan Yang"
    },
    {
      "name": "Huaizhen Li"
    },
    {
      "name": "Ao Wang"
    },
    {
      "name": "Weiwei Na"
    },
    {
      "name": "Hushan Xu"
    },
    {
      "name": "Zhongtao Han"
    },
    {
      "name": "Xiaogu Zhong"
    },
    {
      "name": "Zunli Yuan"
    },
    {
      "name": "Yubin Li"
    },
    {
      "name": "Guangbo Long"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/f0ewevrn2z9qq.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2606.05738",
  "fulltext_url": null,
  "id": "f0ewevrn2z9qq",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2606.05738",
  "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",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2606.05738",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-11",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/f0ewevrn2z9qq.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:29:06Z",
      "native_id": "2606.05738",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2606.05738"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Multi-Period Fermi-LAT and LHAASO Constraints on Axion-Like Particles from Mrk 421 via $χ^2$ Profile Likelihood with Gaussian Copula Correlation",
  "title_text": "Multi-Period Fermi-LAT and LHAASO Constraints on Axion-Like Particles from Mrk 421 via χ^2 Profile Likelihood with Gaussian Copula Correlation",
  "type": "preprint",
  "updated_at": "2026-10-30T12:29:06Z",
  "url": "https://research.draconitic.com/paper/f0ewevrn2z9qq",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1103/jw8n-81yg",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}