We present a fully non-perturbative determination of the $O(a)$ improvement coefficient $c_{rm SW}$ in three-flavor dynamical QCD for the RG improved as well as the plaquette gauge actions, using the Schrodinger functional scheme. Results are compared with one-loop estimates at weak gauge coupling.
We determine the improvement factor $c_{SW}$ in one-loop lattice perturbation theory for the plaquette and Symanzik improved gauge actions. The fermionic action is ${mathcal{O}(a)}$ clover improved with one-time stout smearing. $c_{SW}$ is derived fr
om the one-loop correction to the quark-quark-gluon vertex in the off-shell regime. We give a first numerical value for the one-loop contribution to the non gauge-invariant improvement coefficient $c_{NGI}$ for the quark field using the plaquette action. A discussion of mean field improvement is included.
Using plaquette and Symanzik improved gauge action and stout link clover fermions we determine the improvement coefficient $c_{SW}$ in one-loop lattice perturbation theory from the off-shell quark-quark-gluon three-point function. In addition, we com
pute the coefficients needed for the most general form of quark field improvement and present the one-loop result for the critical hopping parameter $kappa_c$. We discuss mean field improvement for $c_{SW}$ and $kappa_c$ and the choice of the mean field coupling for the actions we have considered.
The non-perturbative $csw$ determined by the Schr{o}dinger functional (SF) method with the RG-improved gauge action in dynamical $N_f=3$ QCD shows a finite volume effect when the numerical simulations are carried out at a constant lattice size $L/a$.
We remove the unwanted finite volume effect by keeping physical lattice extent $L$ at a constant. The details of the method and the result obtained for non-perturbative $csw$ with a constant $L$ are reported.
We perform a non-perturbative determination of the O(a)-improvement coefficient c_SW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of beta=12.0-5.2 on a single lattic
e size of 8^3x16 employing the Schrodinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for c_SW and the critical hopping parameter K_c as a function of the bare coupling. This enables us to remove O(a) scaling violation from physical observables in future numerical simulation in the wide range of beta. Our analysis with a perturbatively modified improvement condition for c_SW suggests that finite volume effects in c_SW are not large on the 8^3x16 lattice. We investigate N_f dependence of c_SW by additional simulations for N_f=4, 2 and 0 at beta=9.6. As a preparatory step for this study, we also determine c_SW in two-flavor QCD at beta=5.2. At this beta, several groups carried out large-scale calculations of the hadron spectrum, while no systematic determination of c_SW has been performed.
The coefficient $c_{rm sw}$ appearing in the Sheikholeslami-Wohlert improved action is computed to one loop perturbation theory for improved gluon actions including six-link loops. The O($a$) improvement coefficients for the dimension three isovector
composite operators bilinear in the quark fields are also computed to one loop order of perturbation theory with degenerate non-vanishing quark masses.