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O. Oliveira

Publications and source records attributed to O. Oliveira.

At least 73 records · Page 4Linked to original sources
arXiv2006

Infrared Gluon and Ghost Propagators from Lattice QCD. Results from large asymmetric lattices

We report on the infrared limit of the quenched lattice Landau gauge gluon and ghost propagators as well as the strong coupling constant computed from large asymmetric lattices. The infrared lattice propagators are compared with the pure power law solutions from Dyson-Schwinger equations (DSE). For the gluon propagator, the lattice data is compatible with the DSE solution. The preferred measured gluon exponent being $\sim 0.52$, favouring a null zero momentum propagator. The lattice ghost propagator shows finite volume effects and, for the volumes considered, the propagator does not follow a pure power law. Furthermore, the strong coupling constant is computed and its infrared behaviour investigated.

hep-lat↗
arXiv2006

Exploring the infrared Landau gauge propagators using large asymmetric lattices

We report on the infrared limit of the quenched lattice Landau gauge gluon and ghost propagators computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solutions of the Dyson-Schwinger equations with the lattice data is investigated and the exponent $κ$ is measured. The gluon lattice data favour $κ\sim 0.52$, which would imply a vanishing zero momentum gluon propagator. For the subset of lattices where the ghost propagator was computed, the data is not compatible with a pure power law. Our data also show a decreasing running coupling in the infrared region. Furthermore, positivity violation for the gluon propagator is also verified.

hep-lat↗
arXiv2006

Studying the infrared behaviour of gluon and ghost propagators using large asymmetric lattices

We report on the infrared limit of the quenched lattice Landau gauge gluon propagator computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solution $(q^2)^{2κ}$ of the Dyson-Schwinger equations is investigated and the exponent $κ$ is measured. Some results for the ghost propagator and for the running coupling constant will also be shown.

hep-lat↗
arXiv2006

Charmonium and Bottomonium from Classical SU(3) Gauge Configurations

The charmonium and bottomonium spectra computed from a potential defined from a single gauge configuration, obtained from solving the classical field equations, is discussed. The theoretical spectra shows good agreement with the measured states. A discussion of possible interpretations, within the same non-relativistic potential model, for the new charmonia states X(3872), $χ_{c1} (2P)$ and Y(4260) is performed. In particular, we give predictions for electromagnetic E1 transitions for various scenarios.

hep-ph↗
arXiv2006

Exploring the infrared gluon and ghost propagators using large asymmetric lattices

We report on the infrared limit of the quenched lattice Landau gauge gluon propagator computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solution $(q^2)^{2κ}$ of the Dyson-Schwinger equations is investigated and the exponent $κ$ is measured. The lattice data favours $κ\sim 0.52$, which would imply a vanishing zero momentum gluon propagator as predicted by the Kugo-Ojima confinement mechanism and the Zwanziger horizon condition. Results for the ghost propagator and for the running coupling constant are shown.

hep-lat↗
arXiv2006

Heavy Quarkonia from Classical SU(3) Yang-Mills Configurations

A generalized Cho-Faddeev-Niemi ansatz for SU(3) Yang-Mills is investigated. The corresponding classical field equations are solved for its simplest parametrization. From these solutions it is possible to define a confining central non-relativistic potential used to study heavy quarkonia. The associated spectra reproduces the experimental spectra with an error of less than 3% for charmonium and 1% for bottomonium. Moreover, the recently discovered new charmonium states can be accomodate in the spectra, keeping the same level of precision. The leptonic width show good agreement with the recent measurements. The charmonium and bottomonium E1 electromagnetic transitions widths are computed and compared with the experimental values.

hep-ph↗
arXiv2006

Charmonium from Classical Pure SU(3) Yang-Mills Configurations

A generalized Faddeev-Niemi ansatz for the gluon field is discussed. In its simplest parametrization, the ansatz allows a solution of the classical SU(3) Yang-Mills equations. From these solutions a confining potential for heavy quarkonia is defined. The investigation of charmonium spectra proves that the potential is able to reproduce the experimental spectra at the level of 3%. Moreover, charmonium leptonic and strong decays are investigated. The results are in fair agreement with experimental figures and are in line with other quark model calculations.

hep-ph↗
arXiv2006

Infrared Gluon Propagator from lattice QCD: results from large asymmetric lattices

The infrared limit of the lattice Landau gauge gluon propagator is studied. We show that the lattice data is compatible with the pure power law $(q^2)^{2 κ}$ solution of the Dyson-Schwinger equations. Using various lattice volumes, the infinite volume limit for the exponent $κ$ is measured. Although, the results allow $κ= 0.498 - 0.525$, the lattice data favours $κ\sim 0.52$, which would imply a vanishing zero momentum gluon propagator.

hep-lat↗
arXiv2006

Flavour changing strong interaction effects on top quark physics at the LHC

We perform a model independent analysis of the flavour changing strong interaction vertices relevant to the LHC. In particular, the contribution of dimension six operators to single top production in various production processes is discussed, together with possible hints for identifying signals and setting bounds on physics beyond the standard model.

hep-ph↗
arXiv2005

The IR gluon propagator from lattice QCD

The gluon propagator is computed in large asymmetric lattices, accessing momenta around 100 MeV and smaller. Our study tries to check the compatibility of the recent solutions of the gluon-ghost Dyson-Schwinger equations with lattice results. In particular the exponent $κ$, which characterizes the solutions for the infrared, is measured. Results favours a vanishing zero momentum gluon propagator. We also report on the compatibility of various functional forms used to fit the Dyson-Schwinger solution for the full range of momenta and the lattice gluon propagator.

hep-lat↗
arXiv2005

Finite volume effects in the gluon propagator

We report on a preliminary study of the volume dependence of the gluon propagator. The propagator is computed using different lattice volumes, its extrapolation to infinite volume is investigated with particular attention to the its IR behaviour. Our data shows a mild but measurable dependence with the volume. Unfortunately, we are not able yet to clarify its behaviour close to zero momentum.

hep-lat↗
arXiv2004

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 $κ$ and $α(0)$ are measured.

hep-lat↗
arXiv2004

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 ($β= 5.8$) $12^4$ 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.

hep-lat↗
arXiv2004

A global optimization method for Landau gauge fixing in Lattice QCD

An algorithm for gauge fixing to the minimal Landau gauge in lattice QCD is described. The method, a combination of an evolutionary algorithm with a steepest descent method, is able to solve the problem of the nonperturbative gauge fixing. The performance of the combined algorithm is investigated on $8^4$, $β= 5.7$, and $16^4$, $β= 6.0$, lattice SU(3) gauge configurations.

hep-lat↗
arXiv2003

Classical Solutions of SU(2) and SU(3) Pure Yang-Mills Theories and Heavy Quark Spectrum

In this paper we compute classical Minkowsky spacetime solutions of pure SU(2) and SU(3) gauge theories, in Landau gauge. The solutions are regular everywhere except at the origin and/or infinity, are characterized by a four momentum $k$ such that $k^2 = 0$ and resemble QED configurations. The classical solutions suggest a particle-independent description of hadrons, similarly to the Atomic and Nuclear energy levels, which is able to reproduce the heavy quarkonium spectrum with a precision below 10%. Typical errors in the theoretical mass prediction relative to the measured mass being of the order of 2-4%.

hep-ph↗
arXiv2002

Classical Solutions of SU(3) Pure Yang-Mills Theory

Regular classical solutions of pure SU(3) gauge theories, in Minkowsky spacetime, are computed in the Landau gauge. The classical fields have an intrinsic energy scale and produce quark confinement if interpreted in the sense of a nonrelativistic potential. Moreover, the quark propagator in the background of these fields vanishes at large positive and negative time and space separations.

hep-th↗
arXiv2001

Gribov Copies and Gauge Fixing in Lattice Gauge Theories

We address the problem of the gauge fixing versus Gribov copies in lattice gauge theories. For the Landau gauge, results show that a suitable combination of evolutionary algorithms with traditional steepest descent methods identifies the global maximum of the optimisation function. We discuss the performance of the combined algorithm on small cubic lattices for SU(2) and SU(3).

hep-lat↗