Thomas DeGrand

QCD spectrum with three quark flavors

We present results from a lattice hadron spectrum calculation using three flavors of dynamical quarks -- two light and one strange -- and quenched simulations for comparison. These simulations were done using a one-loop Symanzik improved gauge action and an improved Kogut-Susskind quark action. The lattice spacings, and hence also the physical volumes, were tuned to be the same in all the runs to better expose differences due to flavor number. Lattice spacings were tuned using the static quark potential, so as a by-product we obtain updated results for the effect of sea quarks on the static quark potential. We find indications that the full QCD meson spectrum is in better agreement with experiment than the quenched spectrum. For the 0{sup ++} (a{sub 0}) meson we see a coupling to two pseudoscalar mesons, or a meson decay on the lattice.

Lattice methods for quantum chromodynamics

Continuum QCD and Its Phenomenology Path Integration Renormalization and the Renormalization Group Yang-Mills Theory on the Lattice Fermions on the Lattice Numerical Methods for Bosons Numerical Methods for Fermions Data Analysis for Lattice Simulations Designing Lattice Actions Spectroscopy Lattice Perturbation Theory Operators with Anomalous Dimension Chiral Symmetry and Lattice Simulations Finite Volume Effects Testing the Standard Model with Lattice Calculations QCD at High Finite Temperature and Density.

Zero of the discrete beta function in SU(3) lattice gauge theory with color sextet fermions

We have carried out a Schrodinger functional calculation for the SU(3) lattice gauge theory with two flavors of Wilson fermions in the sextet representation of the gauge group. We find that the discrete beta function, which governs the change in the running coupling under a discrete change of spatial scale, changes sign when the Schrodinger functional renormalized coupling is in the neighborhood of g{sup 2}=2.0. The simplest explanation is that the theory has an infrared-attractive fixed point, but more complicated possibilities are allowed by the data. While we compare rescalings by factors of 2 and 4/3, we work at a single lattice spacing.

Infrared fixed point in SU(2) gauge theory with adjoint fermions

We apply Schroedinger-functional techniques to the SU(2) lattice gauge theory with N{sub f}=2 flavors of fermions in the adjoint representation. Our use of hypercubic smearing enables us to work at stronger couplings than did previous studies, before encountering a critical point and a bulk phase boundary. Measurement of the running coupling constant gives evidence of an infrared fixed point g{sub *} where 1/g{sub *}{sup 2}=0.20(4)(3). At the fixed point, we find a mass anomalous dimension {gamma}{sub m}(g{sub *})=0.31(6).

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

The classically perfect fixed point action for SU(3) gauge theory

{N}_{f}=2

Running coupling and mass anomalous dimension of SU(3) gauge theory with two flavors of symmetric-representation fermions

flavors of symmetric-representation fermions. The fermions are discretized with the tadpole-improved clover action. Our simulations are done on lattices of length

Conditioning techniques for dynamical fermions

L=6

Phase structure of QCD at high temperature with massive quarks and finite quark density: A Z(3) paradigm

, 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.

Finite-size scaling tests for SU(3) lattice gauge theory with color sextet fermions

In this paper (the first of a series) we describe the construction of fixed-point actions for lattice SU(3) pure gauge theory. Fixed-point actions have scale-invariant instanton solutions and the spectrum of their quadratic part is exact (they are classical perfect actions). We argue that the fixed-point action is even one-loop quantum perfect, i.e. in its physical predictions there are no g2an cut-off effects for any n. We discuss the construction of fixed-point operators and present examples. The lowest-order qq potential V(r) obtained from the fixed-point Polyakov loop correlator is free of any cut-off effects which go to zero as an inverse power of the distance r.