{
  "abstract": "We present a spacetime that serves as a horizonless mimicker of extremal black holes. Unlike previously studied mimickers of black holes with non-degenerate horizons, whose geometries are of the wormhole type and consist of two asymptotically flat regions connected by a very long throat, the mimicker of an extremal black hole possesses a single asymptotically flat region at one end and an infinitely long throat at the other. In the throat region, the spacetime approaches the direct-product geometry $M_{1,1} \\times S^2$, where $M_{1,1}$ is two-dimensional Minkowski spacetime and $S^2$ is the two-sphere. We investigate scalar-field dynamics and the fate of the Aretakis instability. Although Aretakis-like modes arise in a local analysis of the throat, they do not lead to a physical instability of the mimicker. A scalar perturbation initially localized in the throat gives rise, at late times, to a sequence of signals with a characteristic separation $t_{\\rm delay}\\sim 1/λ$, where $λ\\ll 1$ is a deformation parameter. This timescale is parametrically larger than the echo time $t_{\\rm echo}\\sim \\ln(1/λ)$ characteristic of non-extremal black-hole mimickers. We refer to this sequence as a {\\it long-delay signal train}. Geometrically, the periodicity of the long-delay signals is associated with periodic geodesics on $S^2$. We then extend the construction to extremal Kerr. In this case, the throat region approaches a generalized product geometry involving $M_{1,1}$ and a two-dimensional surface $Σ_2$. The corresponding signals are expected to form a quasi-periodic signal train, reflecting the quasi-periodic geodesic motion on $Σ_2$. We also comment on the generalization to wormhole mimickers of non-extremal black holes and on the implications of these results for unitarity in the context of the AdS/CFT correspondence.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.11664",
  "author_total": 1,
  "authors": [
    {
      "name": "Sergey N Solodukhin"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fhqpvhw5wryea.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.11664",
  "fulltext_url": null,
  "id": "fhqpvhw5wryea",
  "issns": [],
  "landing_url": "https://hal.science/hal-05835182v1",
  "language": "en",
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
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  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "gr-qc"
    ],
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      "arxiv",
      "hep-th"
    ],
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      "math-ph"
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    [
      "openalex",
      "3106|Black Holes and Theoretical Physics"
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  ],
  "openalex": "W7221090378",
  "pdf_url": "https://arxiv.org/pdf/2610.11664",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-16",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fhqpvhw5wryea.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:00Z",
      "native_id": "hal-05835182",
      "source": "hal",
      "url": "https://hal.science/hal-05835182v1"
    },
    {
      "first_seen": "2026-10-30T12:30:32Z",
      "native_id": "2610.11664",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.11664"
    }
  ],
  "subjects": [
    {
      "field": "mathematics",
      "origin": "arxiv:math-ph",
      "subfield": "mathematical-physics"
    },
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    },
    {
      "field": "physics",
      "origin": "arxiv:hep-th",
      "subfield": "high-energy"
    }
  ],
  "title": "Extremal black hole mimickers: geometry, stability, and long-delay signal trains",
  "title_text": "Extremal black hole mimickers: geometry, stability, and long-delay signal trains",
  "type": "preprint",
  "updated_at": "2026-10-30T12:33:31Z",
  "url": "https://research.draconitic.com/paper/fhqpvhw5wryea",
  "venue": "HAL",
  "versions": []
}