{
  "abstract": "The simulation of processes that contain multiple particles from the decay of unstable resonances becomes computationally challenging both at leading order and beyond. This paper presents MADSPIN2, a new version of MADSPIN, a dedicated tool tackling this problem, primarily for events generated with the MG5AMC event generator. While still based on the Frixione-Laenen-Motylinski-Webber formalism, the new version leverages spin-density matrices to lift most of the limitations of the previous implementation. It supports loop-induced processes, N -body decays and samples defined by amplitude-level interference between distinct hard-process amplitudes. It also introduces the multiple-pole approximation and a resonance-helicity decomposition, including off-diagonal helicity-interference contributions. These developments substantially broaden the phenomenological scope of MADSPIN, enabling applications that were previously inaccessible within the framework, several of which are demonstrated in this work.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.02794",
  "author_total": 3,
  "authors": [
    {
      "name": "Spyros Argyropoulos"
    },
    {
      "name": "Valentin Durupt"
    },
    {
      "name": "Olivier Mattelaer"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7m3erqsrg1apb.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.02794",
  "fulltext_url": null,
  "id": "7m3erqsrg1apb",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.02794",
  "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",
      "hep-ph"
    ],
    [
      "openalex",
      "3106|Particle physics theoretical and experimental studies"
    ]
  ],
  "openalex": "W7207612773",
  "pdf_url": "https://arxiv.org/pdf/2609.02794",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-02",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7m3erqsrg1apb.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:16Z",
      "native_id": "2609.02794",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.02794"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-ph",
      "subfield": "high-energy"
    }
  ],
  "title": "MadSpin2: automated spin-entangled decays of heavy resonances via the spin-density matrix formalism",
  "title_text": "MadSpin2: automated spin-entangled decays of heavy resonances via the spin-density matrix formalism",
  "type": "preprint",
  "updated_at": "2026-10-30T12:18:16Z",
  "url": "https://research.draconitic.com/paper/7m3erqsrg1apb",
  "venue": "arXiv",
  "versions": []
}