{
  "abstract": "Recent findings from Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillation (BAO) measurements, combined with Type Ia supernovae and Cosmic Microwave Background (CMB) data, suggest potential parameter-level deviations from $Λ\\text{CDM}$. However, parameter exclusions omit prior-volume penalties, whereas Bayesian evidence uncovers a stark dichotomy between early- and late-time dynamics. To quantify this effect, we perform a Bayesian model comparison that explicitly accounts for the cosmological epoch of dark energy dynamics, contrasting two schemes acting in opposite epochs of cosmic history: pre-recombination Early Dark Energy (EDE) and late-time Chevallier--Polarski--Linder (CPL), both measured against a baseline $Λ$CDM. We validate the learned harmonic-mean estimator against UltraNest (at background level) before applying it to the CMB analysis. Background-only data already disfavor both extensions, yielding {$\\ln B_{Λ\\text{CDM},\\text{EDE}} = 1.48 \\pm 0.18$ and $\\ln B_{Λ\\text{CDM},\\text{CPL}} = 2.36 \\pm 0.24$}. Including CMB sharpens this result: {EDE is very strongly rejected ($\\ln B_{Λ\\text{CDM},\\text{EDE}} \\approx 12.61 \\pm 0.17$)} with its early-time fraction constrained to $10^3\\,Ω_e^{\\rm EDE} = 2.0^{+0.6}_{-1.0}$, whereas CPL remains only mildly disfavored ($\\ln B_{Λ\\text{CDM},\\text{CPL}} \\approx 2.34 \\pm 0.18$), even though 2D parameter posteriors for both models display a multi-$σ$ deviation from $Λ\\text{CDM}$. Thus, Bayesian evidence weakens reported preferences for dark energy dynamics, with the impact depending on the cosmic epoch involved, confirmed by our functional reconstructions of $w_{\\rm de}(z)$ and $Ω_{\\rm de}(z)$ from posterior samples.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.05410",
  "author_total": 3,
  "authors": [
    {
      "name": "Miguel A. Zapata"
    },
    {
      "name": "Karim Carrion"
    },
    {
      "name": "Gabriela Garcia-Arroyo"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/09ps9bs1f1eh6.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.05410",
  "fulltext_url": null,
  "id": "09ps9bs1f1eh6",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.05410",
  "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",
      "astro-ph.CO"
    ],
    [
      "openalex",
      "3103|Cosmology and Gravitation Theories"
    ]
  ],
  "openalex": "W7211893387",
  "pdf_url": "https://arxiv.org/pdf/2609.05410",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-24",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/09ps9bs1f1eh6.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:52Z",
      "native_id": "2609.05410",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.05410"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    }
  ],
  "title": "Early against Late: A contrast on dark energy in the light of DESI DR2",
  "title_text": "Early against Late: A contrast on dark energy in the light of DESI DR2",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:52Z",
  "url": "https://research.draconitic.com/paper/09ps9bs1f1eh6",
  "venue": "arXiv",
  "versions": []
}