Strong-isospin violation in the neutron–proton mass difference from fully-dynamical lattice QCD and PQQCD Original Research Article

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 image, lattice spatial size of image and pion masses ranging from image to image. At the physical value of the pion mass, we predict image where the first error is statistical, the second error is due to the uncertainty in the ratio of light-quark masses, image, determined by MILC [C. Aubin, et al., MILC Collaboration, Phys. Rev. D 70 (2004) 114501, hep-lat/0407028], and the third error is an estimate of the systematic due to chiral extrapolation.