{
  "abstract": "Future neutral hydrogen (HI) intensity mapping (IM) and optical surveys probe large-scale structure over unprecedented volumes, offering powerful constraints on cosmological models. We study the cross-correlation between the HI IM field and the galaxy density and cosmic shear fields from optical surveys. By formulating the HI-HI-galaxy and HI-HI-shear cross-bispectra, we recover sensitivity to long-wavelength radial modes otherwise removed by foreground subtraction in HI maps, evaluating their detectability for HIRAX and Rubin-LSST. Combining the probes breaks degeneracies in redshift-dependent quantities, including the $f$-$σ_8$ degeneracy. Our constraints range from $0.74\\%$ to $9.8\\%$ on $f$ and $0.073\\%$ to $3.5\\%$ on $σ_8$ across the six redshift bins that we consider. Our constraints on the first- and second-order HI bias parameters range from $0.42\\%$ to $5.6\\%$ on $b_{\\rm HI}^{(1)}$ and from $2.0\\%$ to $29\\%$ on $b_{\\rm HI}^{(2)}$, while the galaxy bias constraints range from $2.6\\%$ to $11\\%$ on $b_{\\rm gal}.$ The HI-HI-galaxy density cross-bispectrum measurement allows us to constrain a linear scale-dependent model for the stochastic cross-correlation coefficient between HI and stars, $r_{{\\rm HI \\,HI\\,}δ_g} = r_0 + r_1 k,$ with a break scale of $0.14\\,\\mbox{Mpc}^{-1}.$ We obtain $r_0$ constraints that range from $3.8\\%$ to $13.5\\%$ and $r_1$ constraints that range from $7.5\\%$ to $19.9\\%$. For cosmology, adding cross-bispectra enhances Lambda CDM constraints, notably via the HI-HI-shear cross-bispectrum. For the $w_0\\, w_a$CDM model, the power-spectrum-only constraints on $w_0$ and $w_a,$ including Planck priors, improve from $(σ_{w_0},σ_{w_a})=(0.036,0.15)$ and $(0.032,0.12)$ to $(σ_{w_0},σ_{w_a})=(0.014,0.057)$ and $(0.015,0.059)$ when adding the HI-HI-galaxy and HI-HI-shear cross-bispectra, respectively.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.25389",
  "author_total": 3,
  "authors": [
    {
      "name": "Warren Naidoo"
    },
    {
      "name": "Moumita Aich"
    },
    {
      "name": "Kavilan Moodley"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/077nms2gyynet.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.25389",
  "fulltext_url": null,
  "id": "077nms2gyynet",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.25389",
  "language": null,
  "licence": "CC0-1.0",
  "licence_label": "CC0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/publicdomain/zero/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.CO"
    ],
    [
      "arxiv",
      "gr-qc"
    ],
    [
      "openalex",
      "3103|Cosmology and Gravitation Theories"
    ]
  ],
  "openalex": "W7214106627",
  "pdf_url": "https://arxiv.org/pdf/2609.25389",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-21",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/077nms2gyynet.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:39Z",
      "native_id": "2609.25389",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.25389"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    },
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "Cross-Bispectrum Constraints from HI Intensity Mapping and Galaxy Surveys",
  "title_text": "Cross-Bispectrum Constraints from HI Intensity Mapping and Galaxy Surveys",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:39Z",
  "url": "https://research.draconitic.com/paper/077nms2gyynet",
  "venue": "arXiv",
  "versions": []
}