{
  "abstract": "We investigate linear matter-density perturbations in full quadratic gravity. Working in the longitudinal gauge and adopting the sub-horizon and quasi-static approximations, we obtain an algebraic expression for the effective gravitational coupling in the theory and the equation for evolution of matter density perturbations. We identify the positive-real poles of this coupling and map their dependence on the quadratic couplings. In the formal infrared continuation, the reduced coupling recovers its general-relativistic value, whereas at large physical wavenumber it is suppressed when both quadratic couplings are nonzero; the single-coupling limits reproduce distinct behaviors. Numerical integrations of the growing mode are performed up to the first pole and show that pole-free regions of the reduced system can support regular matter-growth solutions, while poles obstruct a continuous late-time evolution. Our results show that quadratic gravity cannot generally reproduce the standard cosmological evolution of perturbations and in the regions where it can, it closely matches the behavior of $f(R)$ theories.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.29046",
  "author_total": 1,
  "authors": [
    {
      "name": "Pedro Bessa"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/30xw4v73kzcj3.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.29046",
  "fulltext_url": null,
  "id": "30xw4v73kzcj3",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.29046",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.CO"
    ],
    [
      "arxiv",
      "gr-qc"
    ],
    [
      "openalex",
      "3103|Cosmology and Gravitation Theories"
    ]
  ],
  "openalex": "W7214346227",
  "pdf_url": "https://arxiv.org/pdf/2609.29046",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-24",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/30xw4v73kzcj3.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:11Z",
      "native_id": "2609.29046",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.29046"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    },
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "Matter density perturbations in Quadratic Gravity",
  "title_text": "Matter density perturbations in Quadratic Gravity",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:11Z",
  "url": "https://research.draconitic.com/paper/30xw4v73kzcj3",
  "venue": "arXiv",
  "versions": []
}