Workshop on the Physics of Excited Nucleon – NSTAR2009, Beijing, April 19 – 22, 2009

Invited plenary talk

Invited parallel talk

Oral contribution

Authors: Toru T. Takahashi and Teiji Kunihiro

Title: Axial charges of N(1535) and N(1650) in two-flavor lattice QCD

Keywords: N(1535), N(1650), axial charge, lattice QCD

Abstract:
We show the lattice QCD results on the axial charges of N(1535) and N(1650). The measurements are performed with two flavors of dynamical quarks employing the renormalization-group improved gauge action at $\beta$=1.95 and the mean-field improved clover quark action with the hopping parameters, $\kappa$=0.1375, 0.1390 and 0.1400. In order to properly separate signals of N(1535) and N(1650), we construct 2x2 correlation matrices and diagonalize them. Wraparound contributions in the correlator, which can be another source of signal contaminations, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N(1535) takes small values as $g_A \sim {\mathcal O}(0.1)$, whereas that of N(1650) is about 0.5, which are almost independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.