{
  "abstract": "Cyclic cosmologies replace inflation's single creation event with an eternal sequence of smooth turnarounds, but three problems have historically stood in their way: singular bounces, the blue tilt generic to single-field ekpyrotic contraction, and Tolman's observation that entropy production should make successive cycles longer and larger without bound. We resolve all three within one explicit model. A Randall-Sundrum brane with a timelike extra dimension regularizes the bounce without violating the null energy condition, and a single scalar field's potential carries the universe from a thawing dark-energy plateau through a sign-changing turnaround into a BKL-safe ekpyrotic contraction and back. We show that no correction internal to the brane's Friedmann equation, and no straight two-field trajectory, can rescue the spectral index from the generic ekpyrotic result $n_s\\approx3$. We then build the minimal completion that can: a kinetically coupled entropy field, following the general mechanism of Ijjas, Lehners, and Steinhardt, whose coupling steepness has a closed-form, exact-scale-invariance value for this model's ekpyrotic potential, with only a percent-level offset needed to match the measured tilt $n_s=0.9649$. This fixes the local non-Gaussianity ($f_{\\rm NL}\\approx-0.02$) and tensor-to-scalar ratio ($r\\approx7.6\\times10^{-26}$). Matching the observed amplitude fixes the conversion coupling and brane tension to unremarkable values ($λ\\approx5.7\\times10^{-3}$, $ρ_c^{1/4}=10^{13}\\,$GeV). Finally, because the brane construction is spatially flat, Tolman's entropy argument does not bound the number of cycles here: we derive $N_{\\rm DE}\\sim70$-80 e-folds of accelerated expansion needed each cycle to dilute the entropy produced back to a negligible density before the next contraction.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.06485",
  "author_total": 1,
  "authors": [
    {
      "name": "Rikpratik Sengupta"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/b5y5ssfmwq8em.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.06485",
  "fulltext_url": null,
  "id": "b5y5ssfmwq8em",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.06485",
  "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"
    ],
    [
      "arxiv",
      "hep-th"
    ],
    [
      "openalex",
      "3103|Cosmology and Gravitation Theories"
    ]
  ],
  "openalex": "W7211995532",
  "pdf_url": "https://arxiv.org/pdf/2609.06485",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-06",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/b5y5ssfmwq8em.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:19:48Z",
      "native_id": "2609.06485",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.06485"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    },
    {
      "field": "physics",
      "origin": "arxiv:hep-th",
      "subfield": "high-energy"
    }
  ],
  "title": "Cycles Without End: An Ekpyrotic Braneworld Bounce with a Kinetically Coupled Entropic Mechanism",
  "title_text": "Cycles Without End: An Ekpyrotic Braneworld Bounce with a Kinetically Coupled Entropic Mechanism",
  "type": "preprint",
  "updated_at": "2026-11-06T18:21:01Z",
  "url": "https://research.draconitic.com/paper/b5y5ssfmwq8em",
  "venue": "arXiv",
  "versions": []
}