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P. J. Silva

Publications and source records attributed to P. J. Silva.

At least 37 records · Page 2Linked to original sources
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

Force Gradient Integrators

We present initial results of the use of Force Gradient integrators for lattice field theories. These promise to give significant performance improvements, especially for light fermions and large lattices. Our results show that this is indeed the case, indicating a speed-up of more than a factor of two, which is expected to increase as the integration step size becomes smaller for larger lattices and smaller fermion masses.

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↗
arXiv2008

Tuning HMC using Poisson brackets

We discuss how the integrators used for the Hybrid Monte Carlo (HMC) algorithm not only approximately conserve some Hamiltonian $H$ but exactly conserve a nearby shadow Hamiltonian (\tilde H), and how the difference $ΔH \equiv \tilde H - H $ may be expressed as an expansion in Poisson brackets. By measuring average values of these Poisson brackets over the equilibrium distribution $\propto e^{-H}$ generated by HMC we can find the optimal integrator parameters from a single simulation. We show that a good way of doing this in practice is to minimize the variance of $ΔH$ rather than its magnitude, as has been previously suggested. Some details of how to compute Poisson brackets for gauge and fermion fields, and for nested and force gradient integrators are also presented.

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↗
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

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

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↗
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↗