{
  "abstract": "We study the propagation of a neutral vector test field non-minimally coupled to the Einstein tensor on a Reissner--Nordström black hole. The interaction vanishes on a vacuum background, so electric charge is required to activate the curvature-induced response. The parity potentials have one symmetry: reversing the sign of the coupling exchanges the electric and magnetic susceptibilities. Because of this symmetry, the two polarizations respond identically at first order in the coupling. The dominant propagation-level effect is therefore a common shift of the effective photon sphere and of the shadow radius, not a birefringent splitting. The variation of shadow size can mimic the charge variation of a black hole. When the coupling is weak, polarization splitting appears only in the second-order term, distinguishing this interaction from corrections involving only charge. We follow this ordering through full-frequency absorption and scattering, the semiclassical glory, and ray-traced double shadows. The absorption parity asymmetry and the shadow rim splitting probe the difference between the effective potentials. The polarization-summed backward scattering isolates the helicity-reversing response, which is zero without the coupling. At the positive-coupling boundary the splitting grows but stays finite. Beyond it the even-parity potential has a pole outside the horizon. In the high-multipole limit, the two boundaries of the stability window both correspond to the thresholds of bound-state instability, but their physical properties differ: the negatively coupled boundary forms a regular potential well, while the positively coupled boundary marks the breaking of regularity. A Frobenius analysis shows a forced logarithmic branch at that pole. Without an additional physical connection condition, the continuation across the pole is not unique.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.16650",
  "author_total": 2,
  "authors": [
    {
      "name": "Mao-Yuan Wan"
    },
    {
      "name": "Chen Wu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/6vkwqdx3bjvn9.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.16650",
  "fulltext_url": null,
  "id": "6vkwqdx3bjvn9",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.16650",
  "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",
      "gr-qc"
    ],
    [
      "openalex",
      "3106|Black Holes and Theoretical Physics"
    ]
  ],
  "openalex": "W7221789142",
  "pdf_url": "https://arxiv.org/pdf/2610.16650",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-16",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6vkwqdx3bjvn9.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:30:32Z",
      "native_id": "2610.16650",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.16650"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "Charge-activated birefringence of an Einstein-tensor-coupled vector field on Reissner--Nordström black holes",
  "title_text": "Charge-activated birefringence of an Einstein-tensor-coupled vector field on Reissner--Nordström black holes",
  "type": "preprint",
  "updated_at": "2026-10-30T12:33:28Z",
  "url": "https://research.draconitic.com/paper/6vkwqdx3bjvn9",
  "venue": "arXiv",
  "versions": []
}