Remarks on the Gauge Dependence of the RI/MOM Renormalization Procedure

The RI/MOM non-perturbative renormalization scheme is studied on the lattice in SU(3) quenched QCD with Wilson fermions. The gauge dependence of some fermion bilinear renormalization constants is discussed by comparing data which have been gauge-fixed in two different realizations of the Landau gauge and in a generic covariant gauge. The very good agreement between the various sets of results and the theory indicates that the numerical uncertainty induced by the lattice gauge-fixing procedure is moderate and below the statistical errors.Comment: 11 pages, 3 figure

Glueballs and mesons in the superfluid phase of two-color QCD

QCD with two colors undergoes a transition to a superfluid phase with diquark condensate when the quark chemical potential equals half the pion mass. We investigate the gluonic aspects of the transition by inspecting the behavior of the glueball correlators evaluated via a multi-step smearing procedure for several values of chemical potential ranging between zero and the saturation threshold. The results are based on an analysis of 0++ glueball correlators, on a sample of 40000 independent configurations on each parameter set. The amplitudes of the correlators peak for \mu = m_\pi/2,indicating that the superfluid phase transition affects the gluonic sector as well. The mass of the fundamental state decreases in the superfluid phase, and the amplitude of the propagators drops, suggesting a reduction of the gluon condensate, in agreement with model calculations. The analysis of the smearing dependence of the results helps disentangling the role of long and short distance phenomena at the superfluid transition.Comment: 7 pages, 5 figures, talk presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4, 2007, Regensburg,German

SU(2) Glueballs, diquarks and mesons in dense matter

We present preliminary results from a high statistics study of 2-color QCD at low temperature and non-zero baryon density. The simulations are carried out on a 6^3*12 lattice and use a standard hybrid molecular dynamics algorithm for staggered fermions for two values of quark mass. Observables include glueball correlators evaluated via a multi-step smearing procedure as well as scalar and vector mesons and diquarks.Comment: Poster presented at Lattice 2003 (Non zero temperature and density), 3 pages, 4 figure

How To Fix Non-Perturbatively A Parameter Dependent Covariant Gauge On The Lattice

We describe how to overcome some problems that usually prevent from obtaining an efficient algorithm to fix a generic covariant gauge on the lattice. This gauge is the lattice equivalent of the generic gauge usually adopted in perturbative calculations. It depends on a parameter whose value can be varied in order to check the gauge dependence of measured matrix elements.Comment: 3 pages, 2 eps figures, LATTICE 9

On the Definition of Gauge Field Operators in Lattice Gauge-Fixed Theories

We address the problem of defining the gauge four-potential on the lattice, in terms of the natural link variables. Different regularized definitions are shown, through non perturbative numerical computation, to converge towards the same continuum renormalized limit.Comment: 8 pages, LaTeX2e/LaTeX209, 3 eps figure

Glue Ball Masses and the Chameleon Gauge

We introduce a new numerical technique to compute mass spectra, based on difference method and on a new gauge fixing procedure. We show that the method is very effective by test runs on a $SU(2)$ lattice gauge theory.Comment: latex format, 10 pages, 4 figures added in uufiles forma

Lattice Gauge Fixing for Parameter Dependent Covariant Gauges

We propose a non-perturbative procedure to fix generic covariant gauges on the lattice. Varying the gauge parameter, this gauge fixing provides a concrete method to check numerically the gauge dependence of correlators measured on the lattice. The new algorithm turns out to converge with a good efficiency. As a preliminary physical result, we find a sensitive dependence of the gluon propagator on the gauge parameter.Comment: 10 pages (LaTeX2e), 5 eps figure

Quark and Gluon Propagators in Covariant Gauges

We present data for the gluon and quark propagators computed in the standard lattice Landau's gauge and for three values of the covariant gauge-fixing parameter lambda=0,8,16. Our results are obtained using the SU(3) Wilson action in the quenched approximation at beta=6.0 and volume=16^3x32.Comment: Lattice2001(theorydevelop

Non perturbative renormalization in coordinate space

We present an exploratory study of a gauge-invariant non-perturbative renormalization technique. The renormalization conditions are imposed on correlation functions of composite operators in coordinate space on the lattice. Numerical results for bilinears obtained with overlap and O(a)-improved Wilson fermions are presented. The measurement of the quark condensate is also discussed.Comment: Lattice2003(improve), 3 page