Overlap valence on 2+1 flavor domain wall fermion configurations with deflation and low-mode substitution

The overlap fermion propagator is calculated on 2+1 flavor domain-wall fermion gauge configurations on 163×32, 243×64 and 323×64 lattices. With hyper-cubic (HYP) smearing and low eigenmode deflation, it is shown that the inversion of the overlap operator can be expedited by ∼20 times for the 163×32 lattice and ∼80 times for the 323×64 lattice. The overhead cost for calculating eigenmodes ranges from 4.5 to 7.9 propagators for the above lattices. Through the study of hyperfine splitting, we found that the O(m2a2) error is small and these dynamical fermion lattices can adequately accommodate quark mass up to the charm quark. A preliminary calculation of the low-energy constant Δ_mix which characterizes the discretization error of the pion made up of a pair of sea and valence quarks in this mixed-action approach is carried out via the scalar correlator with periodic and antiperiodic boundary conditions. It is found to be small which shifts a 300 MeV pion mass by ∼10 to 19 MeV on these sets of lattices. We have studied the signal-to-noise issue of the noise source for the meson and baryon. We introduce a new algorithm with Z₃ grid source and low eigenmode substitution to study the many-to-all meson and baryon correlators. It is found to be efficient in reducing errors for the correlators of both mesons and baryons. With 64-point Z₃ grid source and low-mode substitution, it can reduce the statistical errors of the light quark (m_π∼ 200-300MeV) meson and nucleon correlators by a factor of ∼3-4 as compared to the point source. The Z₃ grid source itself can reduce the errors of the charmonium correlators by a factor of ∼3.