Tadpole-improved Clover Action Research Articles

Electrical Conductivity of the Quark-Gluon Plasma Across the Deconfinement Transition

A lattice calculation is presented for the electrical conductivity σ of the QCD plasma with 2+1 dynamical flavors at nonzero temperature. We employ the conserved lattice current on anisotropic lattices using a tadpole-improved clover action and study the behavior of the conductivity over a wide range of temperatures, both below and above the deconfining transition. The conductivity is extracted from a spectral-function analysis using the maximal entropy method, and a discussion of its systematics is provided. We find an increase of σ/T across the transition.

Phase structure of SU(3) gauge theory with two flavors of symmetric-representation fermions

We have performed numerical simulations of SU(3) gauge theory coupled to ${N}_{f}=2$ flavors of symmetric-representation fermions. The fermions are discretized with the tadpole-improved clover action. Our simulations are done on lattices of length $L=6$, 8, and 12. In all simulation volumes we observe a crossover from a strongly coupled confined phase to a weak-coupling deconfined phase. Degeneracies in screening masses, plus the behavior of the pseudoscalar decay constant, indicate that the deconfined phase is also a phase in which chiral symmetry is restored. The movement of the confinement transition as the volume is changed is consistent with avoidance of the basin of attraction of an infrared fixed point of the massless theory.

A lattice study of Λ b semileptonic decay

We present results from a lattice study of the semileptonic decay Λ b → Λ clν l . We use O(a 2, α sa 2) improved quenched lattices of the MILL collaboration, with lattice spacing ∼ 0.13 fm. For the valence quarks, the tadpoleimproved clover action is used, with the Fermilab method employed for the heavy quarks. Form factors are extracted from the vector as well as the axial-vector part of the current.

Sea quark effects inBspectroscopy and decay constants

We present comprehensive results for the spectrum and decay constants of hadrons containing a single b quark. The heavy quark is simulated using an $O(1/M)$ NRQCD action and the light quark using the $O(a)$ tadpole-improved clover action on gauge configurations containing two degenerate flavours of sea quarks at $\beta^{n_f=2}=5.6$ provided by the HEMCGC collaboration. We present detailed results for the lower lying $S$ and $P$ wave $B$ meson states and the $\Lambda_b$ baryon. We find broad agreement with experiment. In addition, we present results for the pseudoscalar and, for the first time, the vector decay constants fully consistent to $O(\alpha/M): f_B = 186(5)(stat)(19)(pert)(9)(disc)(13)(NRQCD)(+50)(a^{-1})MeV, f_B^* = 181(6) (stat)(18)(pert)(9)(disc)(13)(NRQCD)(+55)(a^{-1})MeV$ and $f_{B_s}/f_B = 1.14(2)(stat)(-2)(\kappa_s)$. We present an investigation of sea quark effects in the $B$ spectrum and decay constants. We compare our results with those from similar quenched simulations at $\beta^{n_f=0}=6.0$. For the spectrum, the quenched results reproduce the experimental spectrum well and there is no significant difference between the quenched and $n_f=2$ results. For the decay constants, our results suggest that sea quark effects may be large. We find that $f_B$ increases by approximately 25% between $n_f=0$ and $n_f=2$.

Perturbative matching of lattice and continuum heavy-light currents with NRQCD heavy quarks

The temporal and spatial components of the heavy-light vector current and the spatial components of the axial current are expressed in terms of lattice-regulated operators suitable for simulations of B and D mesons. The currents are constructed by matching the appropriate scattering amplitudes in continuum QCD and a lattice model to one-loop order in perturbation theory. In the lattice theory, the heavy quarks are treated using the nonrelativistic (NRQCD) formulation and the light quarks are described by the tadpole-improved clover action. The light quarks are treated as massless. Our currents include relativistic and discretization corrections through O(alpha_s/M, a alpha_s), where M is the heavy-quark mass, a is the lattice spacing, and alpha_s is the QCD coupling. As in our previous construction of the temporal component of the heavy-light axial current, mixing between several lattice operators is encountered at one-loop order, and O(a alpha_s) dimension-four improvement terms are identified.

F B and f B s using NRQCD

This talk summarizes the quenched calculation of f B and f B s presented in [1]. The heavy quark is simulated using an O(1/ M 2) improved NRQCD action, and the tadpole improved clover action is used for the light quarks. The axial current includes the O(1/ M) corrections in one-loop perturbation theory and the O(1/ M 2) ones at tree-level. We discuss the various systematic effects and consistency checks made in the calculation.

Spectroscopy of hadrons with b quarks from lattice NRQCD

Preliminary results from an extensive lattice calculation of the B, B c , and ϒ spectrum at quenched β = 6.0 are presented. The study includes radially and orbitally excited mesons, and baryons containing b quarks. The b quarks are formulated using NRQCD; for light and c quarks, a tadpole-improved clover action is used.

Tests of hypercubic fermion actions

I have performed scaling tests using quenched spectroscopy of a family of fermion actions which have a hypercubic kinetic term, gauge connections built of smeared links, and an anomalous magnetic moment term. These actions show improved rotational invariance compared to the standard Wilson action and to the tadpole-improved clover action. Hyperfine splittings are improved compared to the standard Wilson action (at the level of a factor of three in the lattice spacing), and are about the same as for the tadpole-improved clover action.

Heavy meson spectroscopy at β = 6.0

We present results of a quenched calculation of the heavy-light and quarkonium spectrum using the tadpole improved clover action. We resolve completely the triplet χ P-states in quarkonium systems, and obtain evidence for fine structure of the heavy-light P-states. Approximate scaling of the hyperfine splittings is observed, producing results that are significantly below experiment.

SCRI results with the tadpole-improved clover action

We compare light hadron spectroscopy using the Wilson and Clover fermionic actions. We show that a Clover coefficient chosen using tadpole-improved tree-level perturbation theory effectively eliminates the O(a) discretization errors present in the Wilson action. We find that discretization errors in light spectroscopy for both the Wilson and Clover actions are characterized by an energy scale mu of about 200-300 MeV, indicating that these errors can be reduced to the 5% level by using the Clover action at an inverse lattice spacing of about 1.3 GeV.

B and Bc mesons with NRQCD and Clover actions

We present preliminary results from our study of the heavy-light spectrum and decay constants. For the heavy quark, we use NRQCD at various masses around and above the b quark mass. For the first time, the heavy quark action and the heavy-light current consistently include corrections at second order in the non-relativistic expansion, as well as the leading finite a corrections. The light quarks are simulated using a tadpole-improved Clover action at various masses in the strange and c quark region.

Accurate hadron spectroscopy on blocked configurations by tadpole-renormalized, clover-improved Wilson quark action

We compare the quenched hadron spectrum on blocked and unblocked lattices for the Wilson quark action, the clover action and the tadpole-improved clover action. The latter gives a spectrum markedly closer to the original one, even though the cutoff is 1/a ~ 500 Mev.