The Running Coupling from the Quark-Gluon Vertex

We present results for the QCD running coupling obtained from measuring the quark-gluon vertex in Landau gauge with suitable renormalisation conditions. The issue of discretisation errors arising from the fermion action is discussed.Comment: Talk at Lattice 97, 3 pages, 3 postscript figures, uses espcrc2.st

Quark-gluon vertex in a momentum subtraction scheme

We compute the quark-gluon vertex in quenched QCD, in the Landau gauge using an off-shell mean-field O(a)-improved fermion action. The running coupling is calculated in an `asymmetric' momentum subtraction scheme (MOM~). We obtain a crude estimate for Lambda_MSbar=170+/-65 MeV, which is considerably lower than other determinations of this quantity. However, substantial systematic errors remain.Comment: Lattice2001(improvement); 3 pages, 3 figure

Gluons, quarks and deconfinement at high density

We compute gluon and quark propagators in 2-colour QCD at large baryon chemical potential mu. The gluon propagator is found to be antiscreened in the superfluid, confined phase and screened in the large-mu, deconfined phase. We present the first attempt to determine corresponding electric and magnetic gluon masses. The quark propagator undergoes dramatic modifications in the superfluid region as a result of the formation of a superfluid gap. These modifications include the appearance of zero crossings in the vector part of the (normal) quark propagator, a large suppression of the scalar part, and the emergence of anomalous propagation.Comment: 11 pp, 9 figures; talk presented at QCD-TNT, Trento, 7-11 sep 200

Towards the Continuum Limit of the Overlap Quark Propagator in Landau Gauge

The properties of the momentum space quark propagator in Landau gauge are examined for the overlap quark action in quenched lattice QCD. Numerical calculations were done on two lattices with different lattice spacing $a$ and similar physical volumes to explore the quark propagator in the continuum limit. We have calculated the nonperturbative wavefunction renormalization function $Z(p)$ and the nonperturbative mass function $M(p)$ for a variety of bare quark masses and perform a simple linear extrapolation to the chiral limit. We find the behaviour of $Z(p)$ and $M(p)$ in the chiral limit are in good agreement between the two lattices.Comment: 3 pages, 2 figures, talk, Lattice2002(Chiral Fermion

A lattice study of the quark propagator and vertex function

We report on the status of a study of the quark propagator and quark-gluon vertex in momentum space. Quark propagators have been generated at beta=6.0 using the O(a)-improved Sheikholeslami-Wohlert action and fixed to the Landau gauge. The first results for the quark pole mass and field renormalisation constant are reported, and plans for future work are presented.Comment: 3 pages, uuencoded compressed postscript. Contribution to Lattice '9

Particle distributions in electroweak tachyonic preheating

We consider the out-of-equilibrium (quasi-) particle number distributions of the Higgs and W-fields during electroweak tachyonic preheating. We model this process by a fast quench, and perform classical real-time lattice simulations in the SU(2)-Higgs model in three dimensions. We discuss how to define particle numbers and effective energies using two-point functions in Coulomb and unitary gauge, and consider some of the associated problems. After an initial exponential growth in effective particle numbers, the system stabilises, allowing us to extract effective masses, temperatures and chemical potentials for the particles.Comment: 3 pages, Lattice2003(higgs

Momentum-dependence of charmonium spectral functions from lattice QCD

We compute correlators and spectral functions for J/psi and eta_c mesons at nonzero momentum on anisotropic lattices with Nf=2. We find no evidence of significant momentum dependence at the current level of precision. In the pseudoscalar channel, the ground state appears to survive up to T~450MeV or 2.1T_c. In the vector channel, medium modifications may occur at lower temperatures.Comment: 5 pages, 12 figure