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Register a new userMass and Axial current renormalization in the Schrodinger functional scheme for the RG-improved gauge and the stout smeared $O(a)$-improved Wilson quark actions
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We present the quark mass and axial current renormalization factors for the RG-improved Iwasaki gauge action and three flavors of the stout smeared $O(a)$-improved Wilson quark action. We employ $alpha=0.1$ and $n_{mathrm{step}}=6$ for the stout link smearing parameters and all links in the quark action are replaced with the smeared links. Using the Schr{o}dinger functional scheme we evaluate the renormalization factors at $beta=1.82$ where large scale simulations are being carried out.
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We perform a nonperturbative determination of the $O(a)$-improvement coefficient $c_{rm SW}$ and the critical hopping parameter $kappa_c$ for $N_f$=3, 2, 0 flavor QCD with the RG-improved gauge action using the Schrodinger functional method. In order to interpolate $c_{rm SW}$ 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 $c_{rm SW}$ determined for a fixed lattice size $L/a$ is used in numerical simulations.
We non-perturbatively determine the renormalization factor of the axial vector current in lattice QCD with $N_f=3$ flavors of Wilson-clover fermions and the tree-level Symanzik-improved gauge action. The (by now standard) renormalization condition is derived from the massive axial Ward identity and it is imposed among Schr{o}dinger functional states with large overlap on the lowest lying hadronic state in the pseudoscalar channel, in order to reduce kinematically enhanced cutoff effects. We explore a range of couplings relevant for simulations at lattice spacings of $approx 0.09$ fm and below. An interpolation formula for $Z_A(g_0^2)$, smoothly connecting the non-perturbative values to the 1-loop expression, is provided together with our final results.
We report on a study of the light quark spectrum using an improved gauge action and both Kogut-Susskind and Naik quark actions. We have studied six different lattice spacings, corresponding to plaquette couplings ranging from 6.8 to 7.9, with five to six quark masses per coupling. We compare the two quark actions in terms of the spectrum and restoration of flavor symmetry. We also compare these results with those from the conventional action.
We calculate one-loop renormalization factors of three-quark operators, which appear in the low energy effective Lagrangian of the nucleon decay, for $O(a)$-improved quark action and gauge action including six-link loops. This calculation is required to predict the hadronic nucleon decay matrix elements in the continuum regularization scheme using lattice QCD. We present detailed numerical results of the one-loop coefficients for general values of the clover coefficients employing the several improved gauge actions in the Symanzik approach and in the Wilsons renormalization group approach. The magnitudes of the one-loop coefficients for the improved gauge actions show sizable reduction compared to those for the plaquette action.
We study the finite-temperature phase structure and the transition temperature of QCD with two flavors of dynamical quarks on a lattice with the temporal size $N_t=4$, using a renormalization group improved gauge action and the Wilson quark action improved by the clover term. The region of a parity-broken phase is identified, and the finite-temperature transition line is located on a two-dimensional parameter space of the coupling ($beta=6/g^2$) and hopping parameter $K$. Near the chiral transition point, defined as the crossing point of the critical line of the vanishing pion mass and the line of finite-temperature transition, the system exhibits behavior well described by the scaling exponents of the three-dimensional O(4) spin model. This indicates a second-order chiral transition in the continuum limit. The transition temperature in the chiral limit is estimated to be $T_c = 171(4)$ MeV.
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