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Paulo J. Silva

Publications and source records attributed to Paulo J. Silva.

At least 55 records · Page 3Linked to original sources
arXiv2017

Reply to "Comment on 'Lattice Gluon and Ghost Propagators, and the Strong Coupling in Pure SU(3) Yang-Mills Theory: Finite Lattice Spacing and Volume Effects' "

The quenched gluon and ghost propagator data published in [1] is reanalysed following the suggestion of [2] to resolve the differences between the infrared data of the simulations. Our results confirms that the procedure works well either for the gluon or for the ghost propagator but not for both propagators simultaneously as the observed deviations in the data follow opposite patterns. Definitive conclusions require improving the determination of the (ratios) of lattice spacings. A simple procedure for the relative calibration of the lattice spacing in lattice simulations is suggested.

hep-lat↗
arXiv2017

Triple-gluon and quark-gluon vertex from lattice QCD in Landau gauge

We report on preliminary results for the triple-gluon and the quark-gluon vertex in Landau gauge. Our results are based on two-flavor and quenched lattice QCD calculations for different quark masses, lattice spacings and volumes. We discuss the momentum dependence of some of the vertices's form factors and the deviations from the tree-level form.

hep-lat↗
arXiv2016

Landau gauge gluon vertices from Lattice QCD

In lattice QCD the computation of one-particle irreducible (1PI) Green's functions with a large number (> 2) of legs is a challenging task. Besides tuning the lattice spacing and volume to reduce finite size effects, the problems associated with the estimation of higher order moments via Monte Carlo methods and the extraction of 1PI from complete Green's functions are limitations of the method. Herein, we address these problems revisiting the calculation of the three gluon 1PI Green's function.

hep-lat↗
arXiv2016

Further Evidence For Zero Crossing On The Three Gluon Vertex

The three gluon one particle irreducible function is investigated using lattice QCD simulations over a large region of momentum in the Landau gauge for four dimensional pure Yang-Mills equations and the SU(3) gauge group. The results favor a zero crossing of the gluon form factor for momenta in the range $220 - 260$ MeV. This zero crossing is required to happen in order to have a properly defined set of Dyson-Schwinger equations. It is also shown that in the high momentum region the lattice results are compatible with the predictions of renormalisation group improved perturbation theory.

hep-lat↗
arXiv2016

Lattice Gluon and Ghost Propagators, and the Strong Coupling in Pure SU(3) Yang-Mills Theory: Finite Lattice Spacing and Volume Effects

The dependence of the Landau gauge two point gluon and ghost correlation functions on the lattice spacing and on the physical volume are investigated for pure SU(3) Yang-Mills theory in four dimensions using lattice simulations. We present data from very large lattices up to $128^4$ and for two lattice spacings $0.10$ fm and $0.06$ fm corresponding to volumes of $\sim$ (13 fm)$^4$ and $\sim$ (8 fm)$^4$, respectively. Our results show that, for sufficiently large physical volumes, both propagators have a mild dependence on the lattice volume. On the other hand, the gluon and ghost propagators change with the lattice spacing $a$ in the infrared region, with the gluon propagator having a stronger dependence on $a$ compared to the ghost propagator. In what concerns the strong coupling constant $α_s (p^2)$, as defined from gluon and ghost two point functions, the simulations show a sizeable dependence on the lattice spacing for the infrared region and for momenta up to $\sim 1$ GeV.

hep-lat↗
arXiv2015

Gauge fixing and the gluon propagator in renormalizable xi gauges

Covariant $R_ξ$ gauge fixing is notoriously difficult for large lattice volumes, large $ξ$ and small $N_c$. We thoroughly test different convergence techniques, which allows the gauge fixing of lattice configurations with a total volume of (3.25 fm)$^4$, up to $ξ=0.5$. We are able to study the gluon propagator in the infrared region and its dependence on the gauge fixing parameter $ξ$. As expected, the longitudinal gluon dressing functions stay constant at their tree-level value $ξ$. Similar to the Landau gauge, the transverse $R_ξ$ gauge gluon propagators saturate at a non-vanishing value in the deep infrared for all values of $ξ$ studied. We compare with very recent continuum studies and perform a simple analysis of the found saturation with a dynamically generated effective gluon mass.

hep-lat↗
arXiv2014

Z(N) dependence of the pure Yang-Mills gluon propagator in the Landau gauge near Tc

The Z(N) dependence of the pure Yang-Mills gluon propagator, in the Landau gauge, is investigated at finite temperature for N=3. Special attention will be given to the behaviour near the critical temperature $T_c$. Our simulations show a complex pattern as expected in a first order phase transition. Furthermore, we identify an order parameter directly associated with the breaking of the SU(3) center symmetry.

hep-lat↗
arXiv2014

Many faces of the Landau gauge gluon propagator at zero and finite temperature: positivity violation, spectral density and mass scales

We address several aspects of gluon propagation at zero and finite temperature. In particular, we study the violation of spectral positivity, we discuss a method to extract the Källén-Lehmann spectral density of a particle (be it elementary or bound state) propagator and apply it to compute gluon spectral densities from lattice data. Furthermore, we also consider the interpretation of the Landau gauge gluon propagator at finite temperature as a massive type bosonic propagator.

hep-lat↗
arXiv2013

Spectral densities from the lattice

We discuss a method to extract the Källén-Lehmann spectral density of a particle (be it elementary or bound state) propagator by means of 4d lattice data. We employ a linear regularization strategy, commonly known as the Tikhonov method with Morozov discrepancy principle. An important virtue over the popular maximum entropy method is the possibility to also probe unphysical spectral densities, as, for example, of a confined gluon. We apply our proposal to the SU(3) glue sector.

hep-lat↗
arXiv2013

Källén-Lehmann spectroscopy for (un)physical degrees of freedom

We consider the problem of "measuring" the Källén-Lehmann spectral density of a particle (be it elementary or bound state) propagator by means of 4d lattice data. As the latter are obtained from operations at (Euclidean momentum squared) p^2>=0, we are facing the generically ill-posed problem of converting a limited data set over the positive real axis to an integral representation, extending over the whole complex p^2-plane. We employ a linear regularization strategy, commonly known as the Tikhonov method with Morozov discrepancy principle, with suitable adaptations to realistic data, e.g. with unknown threshold. An important virtue over the (standard) maximum entropy method is the possibility to also probe unphysical spectral densities, as, for example, of a confined gluon. We apply our proposal here to "physical" mock spectral data as a litmus test and then to the lattice SU(3) Landau gauge gluon at zero temperature.

hep-lat↗
arXiv2013

The lattice gluon propagator in Landau gauge at zero and finite temperature

The interplay between the finite volume and finite lattice spacing is investigated using lattice QCD simulations to compute the Landau gauge gluon propagator at zero temperature. Comparing several ensembles with different lattice spacings and physical volumes, we conclude that the dominant effects, in the infrared region, are associated with the use of a finite lattice spacing. The simulations show that decreasing the lattice spacing, while keeping the same physical volume, leads to an enhancement of the infrared gluon propagator. Moreover, we also present results for the Landau gauge gluon propagator at finite temperature.

hep-lat↗
arXiv2013

Landau gauge fixing on the lattice using GPU's

In this work, we consider the GPU implementation of the steepest descent method with Fourier acceleration for Laudau gauge fixing, using CUDA. The performance of the code in a Tesla C2070 GPU is compared with a parallel CPU implementation.

hep-lat↗
arXiv2012

GPU implementation of a Landau gauge fixing algorithm

We discuss how the steepest descent method with Fourier acceleration for Laudau gauge fixing in lattice SU(3) simulations can be implemented using CUDA. The scaling of the gauge fixing code was investigated using a Tesla C2070 Fermi architecture, and compared with a parallel CPU gauge fixing code.

hep-lat↗
arXiv2012

Landau Gauge Fixing on GPUs

In this paper we present and explore the performance of Landau gauge fixing in GPUs using CUDA. We consider the steepest descent algorithm with Fourier acceleration, and compare the GPU performance with a parallel CPU implementation. Using $32^4$ lattice volumes, we find that the computational power of a single Tesla C2070 GPU is equivalent to approximately 256 CPU cores.

hep-lat↗
arXiv2012

Landau Gauge Fixing on GPUs and String Tension

We explore the performance of CUDA in performing Landau gauge fixing in Lattice QCD, using the steepest descent method with Fourier acceleration. The code performance was tested in a Tesla C2070, Fermi architecture. We also present a study of the string tension at finite temperature in the confined phase. The string tension is extracted from the color averaged free energy and from the color singlet using Landau gauge fixing.

hep-lat↗