{
  "abstract": "We present the first QCD determination of an energy-dependent form factor for a two-hadron scattering state. In particular, we calculate the QCD contribution to the forward electromagnetic $π^+π^+ + γ\\toπ^+π^+$ amplitude at $m_π\\approx 400$~MeV using lattice QCD. Because lattice calculations are performed in a finite Euclidean spacetime, where asymptotic scattering states are absent, this amplitude cannot be accessed directly from correlation functions. Instead, we can constrain this and related amplitudes nonperturbatively using a finite-volume formalism that requires two ingredients: the discrete finite-volume spectrum and finite-volume matrix elements of the electromagnetic current. We calculate three-point correlation functions coupling $π^+π^+$ finite-volume states and extract the corresponding electromagnetic matrix elements. Combining these results with the previously determined spectrum, we constrain the infinite-volume $π^+π^+ + γ\\toπ^+π^+$ amplitude in the forward limit. Using constraints from Lorentz symmetry, unitarity, and analyticity, we describe this amplitude in terms of a single real-valued energy-dependent two-hadron form factor. The resulting amplitude and form factor agree with the Ward-Takahashi identity across all energies and moving frames considered, providing the first QCD validation of this finite-volume approach and a pathway toward first-principles studies of the electromagnetic structure and electroweak responses of resonances and multi-hadron bound states.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.04142",
  "author_total": 4,
  "authors": [
    {
      "name": "Felipe G. Ortega-Gama"
    },
    {
      "name": "Raúl A. Briceño"
    },
    {
      "name": "Ivan M. Burbano"
    },
    {
      "name": "Robert G. Edwards"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/6p7arqd3kva7p.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.04142",
  "fulltext_url": null,
  "id": "6p7arqd3kva7p",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.04142",
  "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",
      "hep-lat"
    ],
    [
      "arxiv",
      "hep-ph"
    ],
    [
      "arxiv",
      "nucl-th"
    ],
    [
      "openalex",
      "3106|Quantum Chromodynamics and Particle Interactions"
    ]
  ],
  "openalex": "W7208751812",
  "pdf_url": "https://arxiv.org/pdf/2609.04142",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6p7arqd3kva7p.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:31Z",
      "native_id": "2609.04142",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.04142"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-lat",
      "subfield": "high-energy"
    },
    {
      "field": "physics",
      "origin": "arxiv:nucl-th",
      "subfield": "nuclear"
    }
  ],
  "title": "First Two-Hadron Form Factor from QCD",
  "title_text": "First Two-Hadron Form Factor from QCD",
  "type": "preprint",
  "updated_at": "2026-10-30T12:18:31Z",
  "url": "https://research.draconitic.com/paper/6p7arqd3kva7p",
  "venue": "arXiv",
  "versions": []
}