We present a comprehensive analysis of the electromagnetic form factors of the nucleon from a lattice simulation with two flavors of dynamical O(a)-improved Wilson fermions. A key feature of our calculation is that we make use of an extensive ensembl
e of lattice gauge field configurations with four different lattice spacings, multiple volumes, and pion masses down to m_pi ~ 180 MeV. We find that by employing Kelly-inspired parametrizations for the Q^2-dependence of the form factors, we are able to obtain stable fits over our complete ensemble. Dirac and Pauli radii and the anomalous magnetic moments of the nucleon are extracted and results at light quark masses provide evidence for chiral non-analytic behavior in these fundamental observables.
We present the first calculation of the transverse spin structure of the pion in lattice QCD. Our simulations are based on two flavors of non-perturbatively improved Wilson fermions, with pion masses as low as 400 MeV in volumes up to (2.1 fm)^3 and
lattice spacings below 0.1 fm. We find a characteristic asymmetry in the spatial distribution of transversely polarized quarks. This asymmetry is very similar in magnitude to the analogous asymmetry we previously obtained for quarks in the nucleon. Our results support the hypothesis that all Boer-Mulders functions are alike.
A better understanding of transverse momentum (k_T-) dependent quark distributions in a hadron is needed to interpret several experimentally observed large angular asymmetries and to clarify the fundamental role of gauge links in non-abelian gauge th
eories. Based on manifestly non-local gauge invariant quark operators we introduce process-independent k_T-distributions and study their properties in lattice QCD. We find that the longitudinal and transverse momentum dependence approximately factorizes, in contrast to the behavior of generalized parton distributions. The resulting quark k_T-probability densities for the nucleon show characteristic dipole deformations due to correlations between intrinsic k_T and the quark or nucleon spin. Our lattice calculations are based on N_f=2+1 mixed action propagators of the LHP collaboration.
We present a comprehensive study of the lowest moments of nucleon generalized parton distributions in N_f=2+1 lattice QCD using domain wall valence quarks and improved staggered sea quarks. Our investigation includes helicity dependent and independen
t generalized parton distributions for pion masses as low as 350 MeV and volumes as large as (3.5 fm)^3, for a lattice spacing of 0.124 fm. We use perturbative renormalization at one-loop level with an improvement based on the non-perturbative renormalization factor for the axial vector current, and only connected diagrams are included in the isosinglet channel.
