{
  "abstract": "In the standard model of cosmology, it is assumed that dark matter is pressureless with equation of state $w=0$ and dark energy has $w=-1$. We test these assumptions jointly using DESI DR2 distance measurements, including the recent Lyman-$α$ full-shape Alcock-Paczynski (AP) information, DES supernovae, and two complementary CMB treatment. When constant $w_{dm}$ and $w_{de}$ are varied together, we find $w_{dm}=0.000968^{+0.000501}_{-0.000496}$ and $w_{de}=-0.9380^{+0.0259}_{-0.0262}$ (68%). With an alternative CMB treatment that marginalizes over the lensing spectrum, the corresponding constraints are $w_{dm}=0.000870^{+0.000408}_{-0.000410}$ and $w_{de}=-0.9353^{+0.0258}_{-0.0254}$. Both standard $Λ$CDM values are disfavored at approximately $2σ$ in the joint extension. Neither parameter departs significantly from its standard value when only that parameter is varied. This behavior arises because late-time distances favor $w_{de}>-1$, while maintaining the early-Universe physical matter density requires a compensating positive $w_{dm}$, which changes the mapping to the matter density today. Allowing dynamical dark energy further highlights the complexity of the situation: phantom crossing for dark energy makes $w_{dm}=0$ consistent with the data, whereas a positive $w_{dm}$ preference persists when crossing is forbidden. Interestingly, the Pad'e-$w$ parameterization that provides a flexible description of a class of quintessence models (with no phantom crossing), along with $w_{dm}$ free, is even mildly favored over the phantom-crossing $w_0w_a$ model according to both the best-fit $χ^2$ and the DIC under both CMB treatments. One can conclude that the apparent preference for phantom crossing may instead reflect deviations in the dark-matter sector rather than dark-energy dynamics alone. [abridged]",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: Astrophys. J. Lett. 1010, L12 (2026)",
  "arxiv": "2608.04763",
  "author_total": 2,
  "authors": [
    {
      "name": "Jun-Qian Jiang"
    },
    {
      "name": "Arman Shafieloo"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/cgpn6prjdfx0d.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2608.04763",
  "fulltext_url": null,
  "id": "cgpn6prjdfx0d",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2608.04763",
  "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"
    ],
    [
      "arxiv",
      "gr-qc"
    ],
    [
      "arxiv",
      "hep-th"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2608.04763",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-21",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/cgpn6prjdfx0d.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:54Z",
      "native_id": "2608.04763",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2608.04763"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    },
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    },
    {
      "field": "physics",
      "origin": "arxiv:hep-th",
      "subfield": "high-energy"
    }
  ],
  "title": "Is Dark Matter Really Matter?",
  "title_text": "Is Dark Matter Really Matter?",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:54Z",
  "url": "https://research.draconitic.com/paper/cgpn6prjdfx0d",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.3847/2041-8213/aeaa2a",
      "pid": "5wmq5ag0e60sd",
      "relation": "published-as",
      "title": "Is Dark Matter Really Matter?",
      "venue": "The Astrophysical Journal Letters"
    }
  ]
}