Abstract
We report nucleon mass, isovector vector and axial-vector charges, and tensor and scalar couplings, calculated using two recent 2+1-flavor dynamical domain-wall fermions lattice-QCD ensembles generated jointly by the RIKEN-BNL-Columbia and UKQCD collaborations. These ensembles were generated with Iwasaki $\times$ dislocation-suppressing-determinant-ratio gauge action at inverse lattice spacing of 1.378(7) GeV and pion mass values of 249.4(3) and 172.3(3) MeV. The nucleon mass extrapolates to a value $m_N = 0.950(5)$ GeV at physical point. The isovector vector charge renormalizes to unity in the chiral limit, narrowly constraining excited-state contamination in the calculation. The ratio of the isovector axial-vector to vector charges shows a deficit of about ten percent. The tensor coupling no longer depends on mass and extrapolates to 1.04(5) in $\overline {\rm MS}$ 2-GeV renormalization at physical point, in a good agreement with the value obtained at the lightest mass in our previous calculations and other calculations that followed. The scalar charge, though noisier, does not show mass dependence and is in agreement with other calculations.
Highlights
The RIKEN-BNL-Columbia (RBC) Collaboration and subsequently the joint RBC and UKQCD Collaborations have been investigating nucleon structure using the domain-wall fermion (DWF) quarks on a sequence of quenched [1,2], two-flavor [3], and 2 þ 1-flavor [4,5,6] dynamical DWF ensembles at various mass values [7,8,9,10,11,12]
Isovector vector and axial-vector charges, and tensor and scalar couplings, calculated using two recent 2 þ 1-flavor dynamical domain-wall fermion lattice-QCD ensembles generated jointly by the RIKEN-BNL-Columbia and UKQCD Collaborations
The isovector vector charge renormalizes to unity in the chiral limit, narrowly constraining excited-state contamination in the calculation
Summary
The RIKEN-BNL-Columbia (RBC) Collaboration and subsequently the joint RBC and UKQCD Collaborations have been investigating nucleon structure using the domain-wall fermion (DWF) quarks on a sequence of quenched [1,2], two-flavor [3], and 2 þ 1-flavor [4,5,6] dynamical DWF ensembles at various mass values [7,8,9,10,11,12]. Axial-vector charges, and tensor (guT−d 1⁄4 h1iδu−δd) and scalar (guS−d) couplings calculated using two recent 2 þ 1-flavor dynamical DWF lattice-QCD ensembles generated jointly by the RBC and UKQCD Collaborations with Iwasaki × dislocation-suppressing-determinant-ratio (DSDR) gauge action at β 1⁄4 1.75, a−1 1⁄4 1.378ð7Þ GeV, and pion masses of 249.4(3) and 172.3(3) MeV [11,12], which are significantly lighter than in our previous nucleon works. In our earlier works, calculated with degenerate up- and down-quark masses set to be considerably heavier than physical values [4,5,6], we observed the vector-current form factors behaving reasonably well in trending toward experiments: both Dirac and Pauli mean-squared charge radii and the isovector anomalous magnetic moment appeared to linearly depend on the pion mass squared.
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