Strong-Isospin Violation in the Neutron-Proton Mass Difference from Fully-Dynamical Lattice QCD and PQQCD

TL;DR

This paper uses advanced lattice QCD techniques to precisely calculate the strong-isospin contribution to the neutron-proton mass difference, improving understanding of fundamental nucleon mass splitting.

Contribution

It provides a first-principles determination of the strong-isospin violation in neutron-proton mass difference using fully-dynamical lattice QCD and chiral perturbation theory.

Findings

Predicted neutron-proton mass difference component: 2.26 MeV

Quantified uncertainties from statistical, quark mass ratio, and systematic sources

Demonstrated consistency with experimental and theoretical expectations.

Abstract

We determine the strong-isospin violating component of the neutron-proton mass difference from fully-dynamical lattice QCD and partially-quenched QCD calculations of the nucleon mass, constrained by partially-quenched chiral perturbation theory at one-loop level. The lattice calculations were performed with domain-wall valence quarks on MILC lattices with rooted staggered sea-quarks at a lattice spacing of b=0.125 fm, lattice spatial size of L=2.5 fm and pion masses ranging from m_pi ~ 290 MeV to ~ 350 MeV. At the physical value of the pion mass, we predict M_n - M_p |(d-u) = 2.26 +- 0.57 +- 0.42 +- 0.10 MeV where the first error is statistical, the second error is due to the uncertainty in the ratio of light-quark masses, eta=m_u/m_d, determined by MILC, and the third error is an estimate of the systematic due to chiral extrapolation.