[en] We present a determination of the neutral current weak axial charge $G$${}_A^Z$(0) = –0.654(3)_stat(5)_sys using the strange quark axial charge $G$${}_A^s$(0) calculated with lattice QCD. We then perform a phenomenological analysis, where we combine the strange quark electromagnetic form factor from lattice QCD with (anti)neutrino-nucleon scattering differential cross section from MiniBooNE experiments in a momentum transfer region 0.24 ≲ Q² ≲ 0.71 GeV² to determine the neutral current weak axial form factor $G$${}_A^Z$(Q²) in the range of 0 ≲ Q² ≤ 1 GeV². This yields a phenomenological value of $G$${}_A^Z$(0) = –0.687(89)stat(40)sys. The value of $G$${}_A^Z$(0) constrained by the lattice QCD calculation of $G$${}_A^s$(0), when compared to its phenomenological determination, provides a significant improvement in precision and accuracy and can be used to provide a constraint on the fit to $G$${}_A^Z$(Q²) for Q² > 0. This constrained fit leads to an unambiguous determination of (anti)neutrino-nucleon neutral current elastic scattering differential cross section near Q² = 0 and can play an important role in numerically isolating nuclear effects in this region. We show a consistent description of $G$${}_A^Z$(Q²) obtained from the (anti)neutrino-nucleon scattering cross section data requires a nonzero contribution of the strange quark electromagnetic form factor. We demonstrate the robustness of our analysis by providing a post-diction of the BNL E734 experimental data.

[en] We report the first lattice QCD calculation of the glue spin in the nucleon. The lattice calculation is carried out with valence overlap fermions on 2+1 flavor DWF gauge configurations on four lattice spacings and four volumes including an ensemble with physical values for the quark masses. The glue spin S_G in the Coulomb gauge in the MSbar scheme is obtained with the 1-loop perturbative matching. We find the results fairly insensitive to lattice spacing and quark masses. We also find that the proton momentum dependence of S_G in the range 0≤ p <1.5 GeV is very mild, and we determine it in the large momentum limit to be S_G= 0.251(47)(16) at the physical pion mass in the MSbar scheme at μ^2= 10 GeV^2. If the matching procedure in large momentum effective theory is neglected, S_G is equal to the glue helicity measured in high-energy scattering experiments.

[en] We employ dimension-4 operators to improve the local vector and axial-vector currents and calculate the nucleon isovector axial coupling $g$${{}^3}_A$ with overlap valence on 2 + 1-flavor domain wall fermion (DWF) sea. Using the equality of $g$${{}^3}_A$ from the spatial and temporal components of the axial-vector current as a normalization condition, we find that $g$${{}^3}_A$ is increased by a few percent towards the experimental value. Here, the excited-state contamination has been taken into account with three time separations between the source and sink. The improved axial charges $g$${{}^3}_A$ (24I) = 1.22 (4) (3) and $g$${{}^3}_A$ (32I) = 1.21 (3)(3) are obtained on a 24³ × 64 lattice at pion mass of 330 MeV and a 32³ × 64 lattice at pion mass 300 MeV and are increased by 3.4% and 1.7% from their unimproved values, respectively. We have also used clover fermions on the same DWF configurations and find the same behavior for the local axial charge as that with overlap fermions.

[en] We report a comprehensive analysis of the light and strange disconnected-sea quarks contribution to the nucleon magnetic moment, charge radius, and the electric and magnetic form factors. The lattice QCD calculation includes ensembles across several lattice volumes and lattice spacings with one of the ensembles at the physical pion mass. We adopt a model-independent extrapolation of the nucleon magnetic moment and the charge radius. We have performed a simultaneous chiral, infinite volume, and continuum extrapolation in a global fit to calculate results in the continuum limit. We find that the combined light and strange disconnected-sea quarks contribution to the nucleon magnetic moment is μ_M(DI) = –0.022(11)(09)μ_N and to the nucleon mean square charge radius is 〈r²〉_E(DI) = –0.019 (05)(05) fm² which is about 1/3 of the difference between the 〈r${}_p^2$〉_E of electron-proton scattering and that of a muonic atom and so cannot be ignored in obtaining the proton charge radius in the lattice QCD calculation. Here, the most important outcome of this lattice QCD calculation is that while the combined light-sea and strange quarks contribution to the nucleon magnetic moment is small at about 1%, a negative 2.5(9)% contribution to the proton mean square charge radius and a relatively larger positive 16.3(6.1)% contribution to the neutron mean square charge radius come from the sea quarks in the nucleon. For the first time, by performing global fits, we also give predictions of the light and strange disconnected-sea quarks contributions to the nucleon electric and magnetic form factors at the physical point and in the continuum and infinite volume limits in the momentum transfer range of 0 ≤ Q² ≤ 0.5 GeV².

[en] The structure of generalized parton distributions is determined from light-front holographic QCD up to a universal reparametrization function w(x) which incorporates Regge behavior at small x and inclusive counting rules at x → 1. A simple ansatz for w(x) that fulfills these physics constraints with a single-parameter results in precise descriptions of both the nucleon and the pion quark distribution functions in comparison with global fits. Finally, the analytic structure of the amplitudes leads to a connection with the Veneziano model and hence to a nontrivial connection with Regge theory and the hadron spectrum.