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Register a new userNucleon structure from mixed action calculations using 2+1 flavors of asqtad sea and domain wall valence fermions
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We present high statistics results for the structure of the nucleon from a mixed-action calculation using 2+1 flavors of asqtad sea and domain wall valence fermions. We perform extrapolations of our data based on different chiral effective field theory schemes and compare our results with available information from phenomenology. We discuss vector and axial form factors of the nucleon, moments of generalized parton distributions, including moments of forward parton distributions, and implications for the decomposition of the nucleon spin.
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We calculate the light hadron spectrum in full QCD using two plus one flavor Asqtad sea quarks and domain wall valence quarks. Meson and baryon masses are calculated on a lattice of spatial size $L approx 2.5$texttt{fm}, and a lattice spacing of $a approx 0.124$texttt{fm}, for pion masses as light as $m_pi approx 300$texttt{MeV}, and compared with the results by the MILC collaboration with Asqtad valence quarks at the same lattice spacing. Two- and three-flavor chiral extrapolations of the baryon masses are performed using both continuum and mixed-action heavy baryon chiral perturbation theory. Both the three-flavor and two-flavor functional forms describe our lattice results, although the low-energy constants from the next-to-leading order SU(3) fits are inconsistent with their phenomenological values. Next-to-next-to-leading order SU(2) continuum formulae provide a good fit to the data and yield and extrapolated nucleon mass consistent with experiment, but the convergence pattern indicates that even our lightest pion mass may be at the upper end of the chiral regime. Surprisingly, our nucleon masses are essentially lineaer in $m_pi$ over our full range of pion masses, and we show this feature is common to all recent dynamical calculations of the nucleon mass. The origin of this linearity is not presently understood, and lighter pion masses and increased control of systematic errors will be needed to resolve this puzzling behavior.
We compute the pion electromagnetic form factor in a hybrid calculation with domain wall valence quarks and improved staggered (asqtad) sea quarks. This method can easily be extended to rho-to-gamma-pi transition form factors.
We present new high-statistics results for nucleon form factors at pion masses of approximately 290, 350, 500, and 600 MeV using a mixed action of domain wall valence quarks on an improved staggered sea. We perform chiral fits to both vector and axial form factors and compare our results to experiment.
In order to advance lattice calculations of moments of unpolarized, helicity, and transversity distributions, electromagnetic form factors, and generalized form factors of the nucleon to a new level of precision, this work investigates several key aspects of precision lattice calculations. We calculate the number of configurations required for constant statistical errors as a function of pion mass, describe the coherent sink method to help achieve these statistics, examine the statistical correlations between separate measurements, study correlations in the behavior of form factors at different momentum transfer, examine volume dependence, and compare mixed action results with those using comparable dynamical domain wall configurations. We also show selected form factor results and comment on the QCD evolution of our calculations of the flavor non-singlet nucleon angular momentum.
We report lattice-volume independence of low moments of nucleon structure functions from the coarse RIKEN-BNL-Columbia (RBC) and UKQCD joint dynamical (2+1)-flavor domain-wall fermions (DWF) ensembles at the lattice cut off of (a^{-1}sim1.7) GeV. The isovector quark momentum fraction, (< x >_{u-d}), and helicity fraction, (< x >_{Delta u - Delta d}), both fully non-perturbatively renormalized are studied on two spatial volumes of ((sim {rm 2.7 fm})^3) and ((sim {rm 1.8 fm})^3). Their naturally renormalized ratio, (< x >_{u-d}/< x >_{Delta u - Delta d}), is not affected by any finite-size effect. It does not depend strongly on light quark mass and does agree well with the experiment. The respective absolute values, fully non-perturbatively renormalized, do not show any finite-size effect either. They show trending toward the respective experimental values at the lightest up- and down-quark mass. This trending down to the experimental values appears to be a real physical effect driven by lighter quarks. The observations are in contrast to the huge finite-size effect seen in the axial-current form factors.
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