{
  "abstract": "Quadratic f(R) gravity carries a massive scalar degree of freedom, the scalaron, whose finite range $$\\lambda $$ screens its influence on the geometry outside a compact object. We show that this screening severs the exterior of a black hole from that of a neutron star of the same mass. The correction to the Schwarzschild metric is Yukawa-suppressed, falling as $$e^{-r/\\lambda }$$ instead of polynomially in the coupling, and is therefore invisible to any expansion in powers of that coupling; the exterior is moreover intrinsically isotropic, so that inverting the temporal potential alone, as one does for single-potential solutions, fails to solve the field equations. Applying the Gibbons–Werner Gauss–Bonnet theorem to this geometry, we find the leading deflection angle to be exactly the general-relativistic 4GM/b, with b the impact parameter, the scalaron contributions cancelling identically in the combination that bends light. The first correction carries the unfamiliar signature $$\\lambda ^{-1/2}b^{-3/2}e^{-b/\\lambda }$$, screened beyond the scalaron range and confirmed against direct quadrature to around $$20\\%$$ at $$b=4\\lambda $$, improving to $$7\\%$$ at $$b=12\\lambda $$. What survives is not a difference of degree but of kind. The ingredients that deliver it — namely, non-analyticity in the coupling, the intrinsically isotropic gauge, the closed-form screened correction and the pressure-weighted scalar charge — are obtained within a single, self-consistent derivation here. A static black hole carries no scalar hair, and lenses precisely as general relativity requires; a neutron star acquires a scalar charge weighted by the pressure supporting it against collapse, and does not. Weak lensing therefore closes as a discriminant of the theory, whilst the horizon, as against a material surface, remains one in principle. The observational advantage lies not in bending angles at large impact parameter but in the strong-field imaging of the photon sphere, and in the stellar interior, where the scalar charge is fixed by the equation of state.",
  "abstract_shown": true,
  "affiliations": [
    "Universidad Nacional Autónoma de México",
    "Universidade de Lisboa–UL"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 2,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Yashmitha Kumaran",
      "orcid": "0009-0006-5655-6931"
    },
    {
      "affs": [
        1
      ],
      "name": "Ilídio Lopes",
      "orcid": "0000-0002-5011-9195"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ewa2dzwt50gsc.bib",
  "cited_by": 0,
  "doi": "10.1140/epjc/s10052-026-16565-4",
  "fulltext_url": null,
  "id": "ewa2dzwt50gsc",
  "issns": [
    "1434-6052"
  ],
  "landing_url": "https://link.springer.com/article/10.1140/epjc/s10052-026-16565-4",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0",
  "metadata_licence": null,
  "native_subjects": [
    [
      "feed-journal",
      "physics/high-energy"
    ]
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  "openalex": null,
  "pdf_url": "https://link.springer.com/content/pdf/10.1140/epjc/s10052-026-16565-4.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-05",
  "publisher": "Springer Science and Business Media LLC",
  "ris": "https://research.draconitic.com/paper/ewa2dzwt50gsc.ris",
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    {
      "first_seen": "2026-11-05T18:20:57Z",
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    },
    {
      "first_seen": "2026-11-06T00:20:57Z",
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      "url": "https://link.springer.com/article/10.1140/epjc/s10052-026-16565-4"
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  "subjects": [
    {
      "field": "physics",
      "origin": "feed-journal:physics/high-energy",
      "subfield": "high-energy"
    }
  ],
  "title": "Screened scalar hair and the weak-lensing separation of black holes from neutron stars in quadratic f(R) gravity",
  "title_text": "Screened scalar hair and the weak-lensing separation of black holes from neutron stars in quadratic f(R) gravity",
  "type": "peer-reviewed",
  "updated_at": "2026-11-06T12:20:49Z",
  "url": "https://research.draconitic.com/paper/ewa2dzwt50gsc",
  "venue": "The European Physical Journal C",
  "versions": []
}