Nucleon charges with dynamical overlap fermions

Abstract

We calculate the scalar and tensor charges of the nucleon in $2+1$-flavor lattice QCD, for which the systematics of the renormalization of the disconnected diagram is well controlled. Numerical simulations are performed at a single lattice spacing $a=0.11\text{ }\text{ }\mathrm{fm}$. We simulate four pion masses, which cover a range of ${m}_{\ensuremath{\pi}}\ensuremath{\sim}290--540\text{ }\text{ }\mathrm{MeV}$, and a single strange quark mass close to its physical value. The statistical accuracy is improved by employing the so-called low-mode averaging technique and the truncated solver method. We study up, down, and strange quark contributions to the nucleon charges by calculating disconnected diagrams using the all-to-all quark propagator. Chiral symmetry is exactly preserved by using the overlap quark action to avoid operator mixing among different flavors, which complicates the renormalization of scalar and tensor matrix elements and leads to possibly large contamination to the small strange quark contributions. We also study the nucleon axial charge with a contribution from the disconnected diagram. Our results are in reasonable agreement with experiments and previous lattice studies.