{
  "abstract": "NANOGrav and various pulsar timing array experiments recently reported compelling evidence for a stochastic gravitational wave background (SGWB). Such a background may originate from several astrophysical or cosmological sources. Assuming an inflationary origin, we use the latest NANOGrav 15-year dataset to constrain inflationary parameters, including the tensor spectral index ($n_t$), tensor-to-scalar ratio ($r$), and explore the implications for reheating through constraints on the reheating equation of state ($ω_{\\text{re}}$) and reheating temperature ($T_{\\text{re}}$). We find a preference for an extremely blue-tilted tensor spectrum and a non-instantaneous reheating epoch. Despite no concrete evidence on primordial vacua, inflationary vacuum is commonly assumed to be the Bunch-Davies vacuum. In this work, we study modifications to the GW spectrum arising from a two-parameter Bogoliubov family of non-Bunch-Davies vacua. Within this framework, we find that NANOGrav observations favour a subclass of non-Bunch-Davies vacuum, known as the alpha-vacuum. In addition, our analysis demonstrates that the observations strikingly narrow the range of the parameter $α$ that characterizes the vacua. Our analysis indicates that the NANOGrav data can accommodate both matter- and radiation-like reheating scenarios for the standard Bunch-Davies vacuum case. However, within the non-Bunch-Davies framework considered here, a non-matter-like reheating is preferred because matter-like reheating requires relatively large $α$, violating both the NANOGrav upper bound and the backreaction constraint. We further show that a frequency-dependent parametrization of $α$ beyond a threshold frequency can yield a minimal solution that alleviates the blue-tilted issue. Finally, we highlight the possibility of testing such frequency dependence of $α$ through future GW experiments.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: JCAP 10 (2026) 009",
  "arxiv": "2605.05310",
  "author_total": 3,
  "authors": [
    {
      "name": "Debtosh Chowdhury"
    },
    {
      "name": "Rounak Nath"
    },
    {
      "name": "Sudipta Show"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/46ree9mkr9x7r.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2605.05310",
  "fulltext_url": null,
  "id": "46ree9mkr9x7r",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2605.05310",
  "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",
      "hep-ex"
    ],
    [
      "arxiv",
      "hep-ph"
    ],
    [
      "arxiv",
      "hep-th"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2605.05310",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/46ree9mkr9x7r.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:37Z",
      "native_id": "2605.05310",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2605.05310"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    },
    {
      "field": "physics",
      "origin": "arxiv:hep-ex",
      "subfield": "high-energy"
    }
  ],
  "title": "Constraints on the inflationary vacuum and reheating era from NANOGrav",
  "title_text": "Constraints on the inflationary vacuum and reheating era from NANOGrav",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:37Z",
  "url": "https://research.draconitic.com/paper/46ree9mkr9x7r",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1088/1475-7516/2026/10/009",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}