Nonperturbative $O(a)$ improvement of the Wilson quark action with the RG-improved gauge action using the Schrödinger functional method

Abstract

We perform a nonperturbative determination of the $O(a)$-improvement coefficient $c_{\mathrm{SW}}$ and the critical hopping parameter ${\kappa }_c$ for $N_f$=3, 2, 0 flavor QCD with the RG-improved gauge action using the Schrödinger functional method. In order to interpolate $c_{\mathrm{SW}}$ and ${\kappa }_c$ as a function of the bare coupling, a wide range of $\beta$ from the weak coupling region to the moderately strong coupling points used in large-scale simulations is studied. Corrections at finite lattice size of $O(a/L)$ turned out to be large for the RG-improved gauge action, and hence we make the determination at a size fixed in physical units using a modified improvement condition. This enables us to avoid $O(a)$ scaling violations which would remain in physical observables if $c_{\mathrm{SW}}$ determined for a fixed lattice size $L/a$ is used in numerical simulations.

Comments: 27 pages, 5 figures. Version appearing in PRD. \beta dependence of c_sw and kappa_c in two flavor QCD is reanalyzed with a different fit form while no change is made in the quenched and three-flavor QCD