Two-flavor lattice QCD study of the axial charges of N(1535) and N(1650)

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 larger, quark-model-consistent value for N(1650).

Contribution

It provides novel lattice QCD results for the axial charges of these excited nucleon states, using two-flavor dynamical quarks and advanced correlation matrix techniques.

Findings

Axial charge of N*(1535) is approximately 0.1.

Axial charge of N*(1650) is approximately 0.5.

Results are consistent with naive nonrelativistic quark model predictions.

Abstract

We show the first lattice QCD results on the axial charges $g_A^{N^*N^*}$ 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. We construct 2$\times$2 correlation matrices and diagonalize them so that the signals of $N^*(1535)$ and $N^*(1650)$ are properly separated. 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. The axial charge of $N^*(1535)$ is found to take small values as $g_A^{N^*N^*}\sim {\mathcal O}(0.1)$, whereas that of $N^*(1650)$ is approximately 0.5, which is almost independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.