Overlap valence on2+1flavor 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 Δₘᵢₓ 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--300 MeV) 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.