Gribov copies, Lattice QCD and the gluon propagator

We address the problem of Gribov copies in lattice QCD. The gluon propagator is computed, in the Landau gauge, using 302 ($\beta = 5.8$) $12^4$ configurations gauge fixed to different copies. The results of the simulation shows that: i) the effect of Gribov copies is small (less than 10%); ii) Gribov copies change essentially the lowest momenta components ($q < 2.6$ GeV); iii) within the statistical accuracy of our simulation, the effect of Gribov copies is resolved if statistical errors are multiplied by a factor of two or three. Moreover, when modelling the gluon propagator, different sets of Gribov copies produce different sets of parameters not, necessarily, compatible within one standard deviation. Finally, our data supports a gluon propagator which, for large momenta, behaves like a massive gluon propagator with a mass of 1.1 GeV

The Infrared Landau Gauge Gluon Propagator from Lattice QCD

The quenched Landau gauge gluon propagator is investigated in lattice QCD with large assimetric lattices, accessing momenta as low as $q \sim 100$ MeV or smaller. Our investigation focus on the IR limit of the gluon dressing function, testing the compatibility with recent solutions of the Dyson-Schwinger equations. In particular, the low energy parameters $\kappa$ and $\alpha (0)$ are measured.Comment: 3 pages, 1 figure. Talk given at Quark Confinement and the Hadron Spectrum VI 2004, Italy, 21-25 Sep. References correc

Towards the continuum limit of the lattice Landau gauge gluon propagator

The infrared behaviour of the lattice Landau gauge gluon propagator is discussed, combining results from simulations with different volumes and lattice spacings. In particular, the Cucchieri-Mendes bounds are computed and their implications for D(0) discussed.Comment: 3 pages, 3 figures. Talk given at "Quark Confinement and the Hadron Spectrum IX", Madrid, Spain, August 30th - September 3rd, 201

Gamma Ray Bursts as Cosmological Probes

We discuss the prospects of using Gamma Ray Bursts (GRBs) as high-redshift distance estimators, and consider their use in the study of two dark energy models, the Generalized Chaplygin Gas (GCG), a model for the unification of dark energy and dark matter, and the XCDM model, a model where a generic dark energy fluid like component is described by the equation of state, $p= \omega \rho$. Given that the GRBs range of redshifts is rather high, it turns out that they are not very sensitive to the dark energy component, being however, fairly good estimators of the amount of dark matter in the Universe.Comment: 4 pages, 1 figure, talk presented by P.T.S. at the XV Encontro Nacional De Astronomia e Astrofisica, Lisbon, Portugal, 28-30 July 200