{
  "abstract": "Analytic compact-star models in modified gravity usually borrow the junction conditions of general relativity and fix their constants with radii derived for a particular stellar model. Here we avoid both. We study $\\mathcal{F}(\\mathcal{R})=\\mathcal{R}+α\\mathcal{R}^{2}$ gravity with a Durgapal-Bannerji interior of embedding class one (Karmarkar condition) and a Hayward exterior. Without Birkhoff's theorem, the exterior is an assumption, and we measure its effect with the Hayward metric, which deforms Schwarzschild by a length $\\ell$. The junction conditions of quadratic $\\mathcal{F}(\\mathcal{R})$ gravity fix all constants in closed form in terms of $M$, $R$ and $\\ell$. The condition $p_r(R)=0$ is replaced by continuity of the trace of the extrinsic curvature. The Ricci scalar jumps at the surface, so there is a thin shell with negative surface energy density for $α>0$, a gravitational double layer, and a small radial stress. For this stress to be below 1% of the central pressure we need $α\\lesssim0.2$ km$^{2}$ and $\\ell\\lesssim0.3M$. The interior behaves as a self-bound star. A single surface energy density, $ρ_s=(1.37\\pm0.16)ρ_0$, reproduces PSR J0740+6620, J0437-4715, J0030+0451 and J0614-3329, and for $α=0.1$ km$^{2}$ the model predicts $R_{1.4}=11.5$ km and a maximum mass of $2.9 M_\\odot$. Because $\\ell$ enters surface observables only at order $(\\ell/M)^{2}(M/R)^{3}$, the results carry over to a Schwarzschild exterior. Calibrating instead with strange-star radii of eclipsing X-ray pulsars gives $R_{1.4}\\approx9$ km, which current data rule out.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.39916",
  "author_total": 2,
  "authors": [
    {
      "name": "Furqan Nazeer"
    },
    {
      "name": "Tooba Feroze"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ee6vstxnrh6wb.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.39916",
  "fulltext_url": null,
  "id": "ee6vstxnrh6wb",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.39916",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "gr-qc"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.39916",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-29",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/ee6vstxnrh6wb.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:36:23Z",
      "native_id": "2610.39916",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.39916"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "Self-Bound Anisotropic Stars in $\\mathcal{R}+α\\mathcal{R}^2$ Gravity with a Hayward Exterior: Junction Conditions and NICER Constraints",
  "title_text": "Self-Bound Anisotropic Stars in ℛ+αℛ^2 Gravity with a Hayward Exterior: Junction Conditions and NICER Constraints",
  "type": "preprint",
  "updated_at": "2026-11-01T12:20:45Z",
  "url": "https://research.draconitic.com/paper/ee6vstxnrh6wb",
  "venue": "arXiv",
  "versions": []
}