{
  "abstract": "Can a universe undergo a regular Euclidean-Lorentzian signature transition when the gravitational coupling itself is dynamical? We address this question in scalar-tensor gravity with nonminimal coupling $F(ϕ)R$. Although the spatially flat Friedmann-Lemaitre-Robertson-Walker (FLRW) sector can be mapped to the Einstein frame for $F>0$ and a nondegenerate scalar redefinition, not all transition properties are frame independent. For a finite, positive, and sufficiently regular conformal factor, the existence and transverse character of the type change are preserved, whereas the extrinsic geometry is not. We therefore use the Einstein frame as a solution-generating representation and impose total geodesy in the physical Jordan frame. We construct two exactly integrable classes of solutions. In the oscillator-ghost-oscillator branch, the scalar field is stationary at the transition and Jordan-frame total geodesy follows under suitable regularity assumptions on the conformal factor. In the critical exponential-potential branch, the scalar is generically nonstationary and total geodesy instead requires \\begin{equation*} H_E\\big|_Σ= \\frac12 \\left( \\frac{d\\ln F}{dψ} \\right)_Σ\\dotψ_Σ. \\end{equation*} We also distinguish this condition from the stronger smoothness requirements of a Kossowski-Kriele-type transverse metric. Finally, while the canonical Einstein-frame scalar does not allow effective phantom evolution, the dynamical nonminimal coupling can generate a locally superaccelerating Jordan-frame regime near the transition when $\\left(\\frac{d\\ln F}{dψ}\\right)_Σ>0$ for the chosen oscillator branch. Thus signature change persists beyond Einstein gravity, with regularity and effective cosmological behavior remaining intrinsically frame sensitive.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: J. Math. Phys. 67, 092504 (2026)",
  "arxiv": "2609.08964",
  "author_total": 1,
  "authors": [
    {
      "name": "Yaghoub Heydarzade"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/8ryv2hqmvcqzh.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.08964",
  "fulltext_url": null,
  "id": "8ryv2hqmvcqzh",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.08964",
  "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": null,
  "pdf_url": "https://arxiv.org/pdf/2609.08964",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-08",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/8ryv2hqmvcqzh.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:52Z",
      "native_id": "2609.08964",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.08964"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "Can the Universe Change Signature When Gravity is Dynamical?",
  "title_text": "Can the Universe Change Signature When Gravity is Dynamical?",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:52Z",
  "url": "https://research.draconitic.com/paper/8ryv2hqmvcqzh",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1063/5.0343718",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}