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    "story_id": "mp-2026-09-14-027",
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    "headline": "The Cosmology Fit Started Carrying Its Nuclear Uncertainty",
    "slug": "the-cosmology-fit-started-carrying-its-nuclear-uncertainty",
    "dek": "A joint DESI, Planck and nucleosynthesis pipeline explicitly marginalized the prediction nuisance parameters that earlier combinations often fixed.",
    "summary": "A joint DESI, Planck and nucleosynthesis pipeline explicitly marginalized the prediction nuisance parameters that earlier combinations often fixed.",
    "body_text": "Big Bang nucleosynthesis connects primordial light-element abundances to the baryon density used alongside baryon-acoustic-oscillation and cosmic-microwave-background data. This analysis combines DESI DR2 BAO, Planck and BBN while explicitly marginalizing BBN nuisance parameters. Its fiducial ΛCDM fits place the dimensionless Hubble parameter near 0.68, with the exact value and uncertainty changing by dataset and model; extensions for the effective number of relativistic species remain consistent with the standard neighborhood. The authors emphasize that investigator choices affect joint results and provide a pipeline that propagates BBN prediction uncertainty. It is a methods result, not a resolution of the Hubble tension.",
    "why_it_matters": "A joint DESI, Planck and nucleosynthesis pipeline explicitly marginalized the prediction nuisance parameters that earlier combinations often fixed.",
    "limitations": [
      "Its fiducial ΛCDM fits place the dimensionless Hubble parameter near 0.68, with the exact value and uncertainty changing by dataset and model; extensions for the effective number of relativistic species remain consistent with the standard neighborhood.",
      "It is a methods result, not a resolution of the Hubble tension."
    ],
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    "first_published_at": "2026-09-14T09:00:00.000-04:00",
    "modified_at": "2026-09-14T09:00:00.000-04:00",
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    "source_ids": [
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    "tags": [
      "cosmology",
      "Big Bang nucleosynthesis",
      "DESI"
    ],
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  "sources": [
    {
      "source_id": "source-2026-09-14-016",
      "title": "arXiv preprint 2609.12065",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2609.12065",
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      "accessed_at": "2026-09-14T08:24:00.000-04:00",
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    "title": "The Cosmology Fit Started Carrying Its Nuclear Uncertainty",
    "publisher": "The Machine Press",
    "published_at": "2026-09-14T09:00:00.000-04:00",
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