出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We report isovector form factors and low moments of structure functions of nucleon in numerical
lattice quantum chromodynamics (QCD) from the on-going calculations by the RIKENBNL-
Columbia (RBC) and UKQCD Collaborations with (2+1) dynamical flavors of domain-wall
fermion (DWF) quarks. We calculate the matrix elements with four light quark masses, corresponding
to pion mass values of mp = 330–670 MeV, while the dynamical strange mass is fixed
at a value close to physical, on (2.7 fm)3 spatial volume. We found that our axial charge, gA, at
the lightest mass exhibits a large deviation from the heavier mass results. This deviation seems
to be a finite-size effect as the gA value scales with a single parameter, mp L, the product of pion
mass and linear spatial lattice size. The scaling is also seen in earlier 2-flavor dynamical DWF
and Wilson quark calculations. Without this lightest point, the three heavier mass results show
only very mild mass dependence and linearly extrapolate to gA =1.16(6). We determined the four
form factors, the vector (Dirac), induced tensor (Pauli), axial vector and induced pseudoscalar, at
a few finite momentum transfer values as well. At the physical pion mass the form-factors root
mean square radii determined from the momentum-transfer dependence are 20–30% smaller than
the corresonding experiments. The ratio of the isovector quark momentum to helicity fractions,
hxiu−d/hxiDu−Dd is in agreement with experiment without much mass dependence including the
lightest point. We obtain an estimate, 0.81(2), by a constant fit. Although the individual momentum
and helicity fractions are yet to be renormalized, they show encouraging trend toward
experiment.
