N-to-Delta axial transition form factors from lattice QCD.

We evaluate the N to Delta axial transition form factors in lattice QCD with no dynamical sea quarks, with two degenerate flavors of dynamical Wilson quarks, and using domain wall valence fermions with three flavors of staggered sea quarks. We predict the ratio C(5)(A)(q(2))/C(3)(V)(q(2)) relevant for parity violating asymmetry experiments and verify the off-diagonal Goldberger-Treiman relation.

Nucleon axial charge in full lattice QCD.

The nucleon axial charge is calculated as a function of the pion mass in full QCD. Using domain wall valence quarks and improved staggered sea quarks, we present the first calculation with pion masses as light as 354 MeV and volumes as large as (3.5 fm)3. We show that finite volume effects are small for our volumes and that a constrained fit based on finite volume chiral perturbation theory agrees with experiment within 7% statistical errors.

N-to-delta electromagnetic-transition form factors from lattice QCD.

The magnetic dipole (M1), the electric quadrupole (E2), and the Coulomb quadrupole (C2) amplitudes for gammaN-->Delta are calculated in quenched lattice QCD. Using a new method, which combines an optimal choice of interpolating fields for the Delta and an overconstrained analysis, we obtain statistically accurate results for the dipole form factor and for the ratios R(EM)=E2/M1 and R(SM)=C2/M1, up to momentum transfer squared 1.5 GeV2. We show for the first time, using lattice QCD, that both R(EM) and R(SM) are nonzero and negative, in qualitative agreement with experiment and indicating the presence of deformation in the N/Delta system.

Transverse structure of nucleon parton distributions from lattice QCD.

This work presents the first calculation in lattice QCD of three moments of spin-averaged and spin-polarized generalized parton distributions in the proton. It is shown that the slope of the associated generalized form factors decreases significantly as the moment increases, indicating that the transverse size of the light-cone quark distribution decreases as the momentum fraction of the struck parton increases.

Chiral extrapolation of lattice moments of proton quark distributions.

We present the resolution of a long-standing discrepancy between the moments of parton distributions calculated from lattice QCD and their experimental values. We propose a simple extrapolation formula for the moments of the nonsinglet quark distribution u-d, as a function of quark mass, which embodies the general constraints imposed by the chiral symmetry of QCD. The inclusion of the leading nonanalytic behavior leads to an excellent description of both the lattice data and the experimental values of the moments.