Isovector charges of the nucleon from 2+1+1-flavor lattice QCD

We present high statistics results for the isovector charges g(A)(u-d), g(S)(u-d) and g(T)(u-d) of the nucleon. Calculations were carried out on eleven ensembles of gauge configurations generated by the MILC collaboration using highly improved staggered quarks action with 2 + 1 + 1 dynamical flavors. These ensembles span four lattice spacings a approximate to 0.06, 0.09, 0.12 and 0.15 fm and light-quark masses corresponding to M-pi 135, 225 and 315 MeV. Excited-state contamination in the nucleon three-point correlation functions is controlled by including up to three-states in the spectral decomposition. Remaining systematic uncertainties associated with lattice discretization, lattice volume and light-quark masses are controlled using a simultaneous tit in these three variables. Our final estimates of the isovector charges in the MS scheme at 2 GeV are g(A)(u-d) = 1.218(25)(30), g(S)(u-d) = 1.022(80)(60) and g(T)(u-d) = 0.989(32)(10). The first error includes statistical and all systematic uncertainties except that due to the extrapolation ansatz, which is given by the second error estimate. We provide a detailed comparison with the recent result of g(A)(u-d) = 1.271(13) by the CalLat collaboration and argue that our error estimate is more realistic. Combining our estimate for g(S)(u-d) with the difference of light quark masses (m(d) - m(u))(QCD) = 2.572(66) MeV given by the MILC/Fermilab/TUMQCD collaboration for 2 + 1 + 1-flavor theory, we obtain (M-N - M-P)(QCD) = 2.63(27) MeV. We update the low-energy constraints on novel scalar and tensor interactions, is an element of(s) and is an element of(T), at the TeV scale by combining our new estimates for g(S)(u-d) and g(T)(u-d) with precision low-energy nuclear experiments, and find them comparable to those from the ATLAS and the CMS experiments at the LHC.