{
  "abstract": "We carry out a search for the relative baryon-cold dark matter (CDM) density and velocity modes in the DESI full-shape (FS) data, and investigate whether DESI's preference for evolving dark energy can be affected by these relative perturbations, which are a known contaminant of the baryon acoustic oscillations. For the first time, we use a holistic effective field theory (EFT) treatment of the power spectrum and bispectrum both for the standard terms (without relative perturbations), modeled in EFT to one-loop order, and for the relative perturbations. For the latter we implement an efficient computation of the one-loop power spectrum that allows us to scan over different cosmologies. We obtain robust constraints on the relative density and velocity bias parameters $b_{δ_{bc}}$, and $b_{v^2_{bc}}$ for all the DESI DR1 tracers, finding e.g. $b_{δ_{bc}}=5 \\pm 6$, $b_{v^2_{bc}}=-0.031\\pm 0.023$ (at 68% CL) for the LRG2 sample in a DESI FS-only analysis within $Λ$CDM, supplemented by CMB priors on the baryon density and spectral tilt. Assuming instead a $w_0w_a$CDM cosmological model, and combining DESI FS with the CMB primary anisotropies, CMB lensing, and Pantheon+ supernovae, our LRG2 constraints read $b_{δ_{bc}}=2 \\pm 5$, $b_{v^2_{bc}}=-0.032\\pm 0.022$. Adding the relative velocity divergence biases we find $b_{δ_{bc}}=-17_{-17}^{+19}$, $b_{θ_{bc}}=-760_{-680}^{+700}$, $b_{v^2_{bc}}=-0.032\\pm 0.024$ for the same sample. The constraints on the dark energy equation of state parameters are virtually unchanged when marginalizing over the baryon-CDM modes. We conclude that DESI's preference for evolving dark energy is robust with respect to the baryon-CDM relative perturbations.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.10794",
  "author_total": 6,
  "authors": [
    {
      "name": "Ananda F. Smith"
    },
    {
      "name": "Mikhail M. Ivanov"
    },
    {
      "name": "Roger de Belsunce"
    },
    {
      "name": "Shi-Fan Chen"
    },
    {
      "name": "Anton Chudaykin"
    },
    {
      "name": "Oliver H. E. Philcox"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fv4tnnk92ty8v.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.10794",
  "fulltext_url": null,
  "id": "fv4tnnk92ty8v",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.10794",
  "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": "W7212302764",
  "pdf_url": "https://arxiv.org/pdf/2609.10794",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-09",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fv4tnnk92ty8v.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:26Z",
      "native_id": "2609.10794",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.10794"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    }
  ],
  "title": "$w_0w_a$ or $bc$: DESI constraints on relative baryon-CDM perturbations",
  "title_text": "w_0w_a or bc: DESI constraints on relative baryon-CDM perturbations",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:26Z",
  "url": "https://research.draconitic.com/paper/fv4tnnk92ty8v",
  "venue": "arXiv",
  "versions": []
}