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O. Oliveira

Publications and source records attributed to O. Oliveira.

At least 55 records · Page 3Linked to original sources
arXiv2010

From propagators to glueballs in the Gribov-Zwanziger framework

Over the last years, lattice calculations in pure Yang-Mills gauge theory seem to have come more or less to a consensus. The ghost propagator is not enhanced and the gluon propagator is positivity violating, infrared suppressed and non-vanishing at zero momentum. From an analytical point of view, several groups are agreeing with these results. Among them, the refined Gribov-Zwanziger (RGZ) framework also accommodates for these results. The question which rises next is, if our models hold the right form for the propagators, how to extract information on the real physical observables, i.e. the glueballs? How do the operators which represent glueballs look like? We review the current status of this matter within the RGZ framework.

hep-th↗
arXiv2010

Gluon Mass in Landau Gauge QCD

The interpretation of the Landau gauge lattice gluon propagator as a massive type bosonic propagator is investigated for i) an infrared constant gluon mass; ii) an ultraviolet constant gluon mass; iii) a momentum dependent mass. We find that the infrared data can be associated with a massive propagator with a constant gluon mass of 651(12) MeV, but the ultraviolet lattice data is not compatible this type of propagator. The scenario of a momentum dependent gluon mass gives a decreasing mass with the momentum, starting from a value of $\sim 630$ MeV in the infrared region and suggesting a $q^2 \ln q^2$ dependence for momenta above 1 GeV.

hep-lat↗
arXiv2010

From unphysical gluon and ghost propagators to physical glueball propagators (in the Gribov-Zwanziger picture): a not so trivial task?

During recent years, a good agreement was found between the analytical derivation and the numerical simulation of the Landau gauge gluon and ghost propagators. We mention the Schwinger-Dyson and Gribov-Zwanziger formalism for the analytical work. Although the agreement between several approaches is nice, these propagators do not correspond to the relevant physical degrees of freedom. In the case of pure gauge theories, one should start to study the glueball correlators. We shall try to explain why it looks like a hard challenge to go from the unphysical to the physical propagators in the case of the Gribov-Zwanziger theory (but similar conclusions might hold for other approaches giving similar propagators).

hep-th↗
arXiv2010

Revisiting the Wu-Yang Monopole: classical solutions and conformal invariance

he Wu-Yang monopole for pure SU(2) Yang-Mills theory is revisited. New classical solutions with finite energy are found for a generalized Wu-Yang configuration. Our method relies on known asymptotic series solutions and explores the conformal invariance of the theory to set the scale for the monopole configurations. Furthermore, by breaking the scale invariance of the pure Yang-Mills theory by a term which simulates the coupling to quark fields, four different monopole configurations with an energy of 2.9 GeV and spatial extent of 1.2 fm, 1.4 fm, 2.4 fm and 2.6 fm are obtained. These configurations may play a role in the transition to the plasma phase.

hep-th↗
arXiv2010

Indirect lattice evidence for the Refined Gribov-Zwanziger formalism and the gluon condensate $\braket{A^2}$ in the Landau gauge

We consider the gluon propagator $D(p^2)$ at various lattice sizes and spacings in the case of pure SU(3) Yang-Mills gauge theories using the Landau gauge fixing. We discuss a class of fits in the infrared region in order to (in)validate the tree level analytical prediction in terms of the (Refined) Gribov-Zwanziger framework. It turns out that an important role is played by the presence of the widely studied dimension two gluon condensate $\braket{A^2}$. Including this effect allows to obtain an acceptable fit up to 1 á 1.5 GeV, while corroborating the Refined Gribov-Zwanziger prediction for the gluon propagator. We also discuss the infinite volume extrapolation, leading to the estimate $D(0)=8.3\pm0.5\text{GeV}^{-2}$. As a byproduct, we can also provide the prediction $\braket{g^2 A^2}\approx 3\text{GeV}^2$ obtained at the renormalization scale $μ=10\text{GeV}$.

hep-lat↗
arXiv2009

Schwinger-Dyson equations and the quark-antiquark static potential

In lattice QCD, a confining potential for a static quark-antiquark pair can be computed with the Wilson loop technique. This potential, dominated by a linear potential at moderate distances, is consistent with the confinement with a flux tube, an extended and scalar system also directly observable in lattice QCD. Quantized flux tubes have also been observed in another class of confinement, the magnetic confinement in type II superconductors. On the other hand the solution of Schwinger Dyson Equations, say with the Landau gauge fixing and the truncation of the series of Feynman diagrams, already at the rainbow level for the self energy and at the ladder level for the Bethe Salpeter equation, provides a signal of a possible inverse quartic potential in momentum space derived from one gluon and one ghost exchange, consistent with confinement. Here we address the successes, difficulties and open problems of the matching of these two different perspectives of confinement, the Schwinger-Dyson perspective versus the flux tube perspective.

hep-lat↗
arXiv2009

The lattice infrared Landau gauge gluon propagator: from finite volume to the infinite volume

The Landau gauge lattice gluon propagator is discussed for different sets of lattices. Particular attention is given to its infrared properties. Our results show that the lattice propagator can be made compatible with either the decoupling-like or the scaling-like solution of the Dyson-Schwinger equations. Furthermore, the analysis of the Cucchieri-Mendes bounds is performed onsidering large volume simulations and the Oliveira-Silva ratios are computed. If the first do not give a clear answer about the value of D(0), the second method favors a $D(0) = 0$. Finally, the SU(3) and SU(2) propagators are compared in the infrared. It comes out that the propagators are different although the infrared exponents seem to be similar. The analysis suggests a scaling behaviour $D(0) \sim N$ with the gauge group SU(N).

hep-lat↗
arXiv2009

Does The Lattice Zero Momentum Gluon Propagator for Pure Gauge SU(3) Yang-Mills Theory Vanish in the Infinite Volume Limit?

The Cucchieri-Mendes bounds for the gluon propagator are discussed for the four dimensional pure gauge SU(3) theory. Assuming a pure power law dependence on the inverse of the lattice volume, the lattice data gives a vanishing zero momentum gluon propagator in the infinite volume limit. Our investigation shows that this result is robust against variations of the lattice volumes and corrections to the power law. Moreover, it is consistent with the Gribov-Zwanziger horizon condition and contradicts the SU(2) analysis, which assumed the same type of dependence on the inverse of the volume. Our analysis considers also more general ansatze that, although not conclusive, open the possibility of having $D(0) \ne 0$ in the infinite volume limit. A solution to this puzzle requires further investigations.

hep-lat↗
arXiv2009

Dimension six FCNC operators and top production at the LHC

In this work we calculate the effects of the electroweak flavour changing neutral currents dimension six effective operators on single top production at the LHC. These results are then combined with previous ones we have obtained for the strong sector. This allow us, for the first time, to perform a combined analysis of flavour changing neutral currents in top production with all contributing dimension six operators. Finally, we study the feasibility of their observation and characterization both at the Tevatron and at the LHC.

hep-ph↗
arXiv2008

Exotic static 3-body potentials

We study exotic static 3-body potentials, utilizing generalized Wilson Loops in SU(3) lattice QCD. For the quark-antiquark-gluon techniques we address the angles of 0, 45, 60, 90, 120, 135 and 180 degrees, between the quark-gluon and the antiquark-gluon segments. We calculate the form of the static potential and discuss whether, or not, two-body interactions exist between the three different bodies, and study the existence of repulsion between the strings. We also perform a first study of the interactions in the system of three gluon.

hep-lat↗
arXiv2008

Infrared Gluon and Ghost Propagator Exponents From Lattice QCD

The compatibility of the pure power law infrared solution of QCD and lattice data for the gluon and ghost propagators in Landau gauge is discussed. For the gluon propagator, the lattice data is well described by a pure power law with an infrared exponent $κ\sim 0.53$, in the Dyson-Schwinger notation. $κ$ is measured using a technique that suppresses finite volume effects. This value implies a vanishing zero momentum gluon propagator, in agreement with the Gribov-Zwanziger confinement scenario. For the ghost propagator, the lattice data seem not to follow a pure power law, at least for the range of momenta accessed in our simulation.

hep-lat↗
arXiv2007

Just how different are SU(2) and SU(3) Landau-gauge propagators in the IR regime?

The infrared behavior of gluon and ghost propagators in Yang-Mills theories is of central importance for understanding quark and gluon confinement in QCD. While simulations of pure SU(3) gauge theory correspond to the physical case in the limit of infinite quark mass, the SU(2) case (i.e. pure two-color QCD) is usually employed as a simplification, in the hope that qualitative features be the same as for the SU(3) case. Here we carry out the first comparative study of lattice (Landau) propagators for these two gauge groups. Our data were especially produced with equivalent lattice parameters in order to allow a careful comparison of the two cases. We find very good agreement between SU(2) ans SU(3) propagators, showing that in the IR limit the equivalence of the two cases is quantitative, at least down to about 1 GeV. Our results suggest that the infrared behavior of these propagators is independent of the gauge group SU(N_c), as predicted by Schwinger-Dyson equations.

hep-lat↗
arXiv2007

The gluon propagator from large asymmetric lattices

The Landau-gauge gluon propagator is computed for the SU(3) gauge theory on lattices up to a size of $32^3 \times 200$. We use the standard Wilson action at $β= 6.0$ and compare our results with previous computations using large asymmetric and symmetric lattices. In particular, we focus on the impact of the lattice geometry and momentum cuts to achieve compatibility between data from symmetric and asymmetric lattices for a large range of momenta.

hep-lat↗
arXiv2007

SU(2) meets SU(3) in lattice-Landau-gauge gluon and ghost propagators

A comparative study of the lattice Landau gauge gluon and ghost propagators for SU(2) and SU(3) pure Yang-Mills theories is carried out. The data were specially produced with equivalent lattice parameters to allow for a careful comparison of the two cases. We find very good agreement between the two theories. Our results seem to confirm the predicton of Schwinger-Dyson equations that the infrared exponents are independent of the gauge group SU(N).

hep-lat↗
arXiv2007

Infrared exponents of gluon and ghost propagators from Lattice QCD

The compatibility of the pure power law infrared solution of QCD Dyson-Schwinger equations (DSE) and lattice data for the gluon and ghost propagators in Landau gauge is discussed. For the gluon propagator, the lattice data is compatible with the DSE infrared solution with an exponent $κ\sim0.53$, measured using a technique that suppresses finite volume effects and allows to model these corrections to the lattice data. For the ghost propagator, the lattice data does not seem to follow the infrared DSE power law solution.

hep-lat↗
arXiv2007

Gauge fixing methods and Gribov copies effects in lattice QCD

We compare two Landau gauge fixing methods, aiming to find the global maximum of the gauge fixing functional. Moreover, a systematic effect of Gribov copies in the gluon and ghost propagators computed in Landau gauge is presented and discussed.

hep-lat↗
arXiv2007

First study of the gluon-quark-antiquark static potential in SU(3) Lattice QCD

We study the long distance interaction for hybrid hadrons, with a static gluon, a quark and an antiquark with lattice QCD techniques. A Wilson loop adequate to the static hybrid three-body system is developed and, using a 24^3 x 48 periodic lattice with beta=6.2 and a ~ 0.075 fm, two different geometries for the gluon-quark segment and the gluon-antiquark segment are investigated. When these segments are perpendicular, the static potential is compatible with confinement realized with a pair of fundamental strings, one linking the gluon to the quark and another linking the same gluon to the antiquark. When the segments are parallel and superposed, the total string tension is larger and agrees with the Casimir Scaling measured by Bali. This can be interpreted with a type-II superconductor analogy for the confinement in QCD, with repulsion of the fundamental strings and with the string tension of the first topological excitation of the string (the adjoint string) larger than the double of the fundamental string tension.

hep-lat↗