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Accepted · first revision · record

Title: Two-nucleon binding from lattice QCD at physical quark masses
Plain: The deuteron (a bound proton and neutron) is held together by only 2.2 MeV, while two neutrons do not bind at all. Lattice QCD calculations at heavier-than-real quark masses disagree with each other on whether two nucleons bind.
Precise: Compute the $I=0$ (deuteron) and $I=1$ (dineutron) S-wave nucleon-nucleon phase shifts and pole positions in lattice QCD at the physical pion mass, with continuum and infinite-volume extrapolation. Answer: deuteron binding energy (experiment $2.2246\,\mathrm{MeV}$) and the $1S0$ nn scattering length (experiment about $-18.9\,\mathrm{fm}$), plus resolution of the dependence of results on the choice of interpolating operators found at $m_{\pi}$ above $300\,\mathrm{MeV}$.
Settled by: Variational lattice QCD spectra with complete two-nucleon operator bases at several pion masses down to physical, converted to scattering amplitudes with the Luscher finite-volume method (which maps energies in a finite box to phase shifts).
Kind: well-posed
Answer type: value
References: (empty)
Literature status: contested
Status note: A 2025 calculation with a large operator basis at $m_{\pi}$ about $714\,\mathrm{MeV}$ found no bound dinucleons (BaSc collaboration, arXiv 2505.05547), contradicting earlier deep-binding results obtained with compact hexaquark operators.
Posed since: (empty)