  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 fm. We simulate four pion masses, which cover
a range of $m_\pi \sim$ 290 - 540 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 contribution from the disconnected diagram. Our results are in
reasonable agreement with experiments and previous lattice studies.
