Axial charges of N(1535) and N(1650) in lattice QCD with two flavors of dynamical quarks

TL;DR

This study presents the first lattice QCD calculations of the axial charges of N(1535) and N(1650), revealing small axial charge for N(1535) and a moderate value for N(1650), consistent with quark model predictions.

Contribution

It provides the first lattice QCD results for the axial charges of N(1535) and N(1650), using correlation matrix techniques to distinguish signals and eliminate contamination.

Findings

Axial charge of N(1535) is approximately 0.1.

Axial charge of N(1650) is about 0.5.

Results are independent of quark masses and align with quark model predictions.

Abstract

We show the first lattice QCD results on the axial charge $g_A^{N^*N^*}$ 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 2$\times$2 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 $g_A^{N^*N^*}\sim {\mathcal O}(0.1)$, whereas that of $N^*(1650)$ is about 0.5, which is found independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.