15178500
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.
119119666
Shadow Hamiltonians, Poisson Brackets, and Gauge Theories
Numerical lattice gauge theory computations to generate gauge field configurations including the effects of dynamical fermions are usually carried out using algorithms that require the molecular dynamics evolution of gauge fields using symplectic integrators. Sophisticated integrators are commonly used but hard to optimize, and force-gradient integrators show promise especially for large lattice volumes. We explain that symplectic integrators lead to very efficient Monte Carlo algorithms because they exactly conserve a shadow Hamiltonian. The shadow Hamiltonian may be expanded in terms of Poisson brackets and can be used to optimize the integrators. We show how this may be done for gauge theories by extending the formulation of Hamiltonian mechanics on Lie groups to include Poisson brackets and shadows and by giving a general method for the practical computation of forces, force gradients, and Poisson brackets for gauge theories.
62820378
Glueball spectral densities from the lattice
The propagator of a physical degree of freedom ought to obey a Kallen-Lehmann spectral representation, with positive spectral density. The latter quan tity is directly related to a cross section based on the optical theorem. The spectral density is a crucial ingredient of a quantum field theory with elementary and bound states, with a direct experimental connection as the masses of the excitations reflect themselves into (continuum) δ -singularities. In usual lattice simulational approaches to the QCD spectrum the spectral density itself is not accessed. The (bound state) masses are extracted from the asymptotic exponential decay of the two-point function. Given the importance of the spectral density, each nonperturbative continuum approach to QCD should be able to adequately describe it or to take into proper account . In this work, we wish to present a first trial in extracting an estimate for the scalar glueball spectral density in SU(3) gluodynamics using lattice gauge theory.
119195282
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 in agreement with the Gribov-Zwanziger horizon condition but contradicting the SU(2) analysis. The results are robust against variations of the lattice volumes and corrections to the power law. 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.
119020741
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 (q2)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.
15870244
Landau Gauge Fixing on GPUs and String Tension
CFC,DepartamentodeFisica,FaculdadedeCienciaseTecnologia,UniversidadedeCoimbra,3004-516Coimbra,PortugalWe explore the performance of CUDA in performing Landau gaugeﬁxing in Lattice QCD, using the steepest descent method with Fourieracceleration. The code performance was tested in a Tesla C2070, Fermiarchitecture. Wealsopresentastudyofthestringtensionatﬁnitetemper-atureintheconﬁnedphase. ThestringtensionisextractedfromthecoloraveragedfreeenergyandfromthecolorsingletusingLandaugaugeﬁxing.PACSnumbers: 11.15.Ha;12.38.Gc
15081043
Fixed points and vacuum energy of dynamically broken gauge theories
We show that if a gauge theory with dynamical symmetry breaking has nontrivial fixed points, they will correspond to extrema of the vacuum energy. This relationship provides a different method to determine fixed points.
122619113
Infrared Finite Gluon Propagator and the Structure of Chiral Symmetry Breaking
We study the chiral symmetry breaking in QeD, using an effective potential for composite operators, with infrared finite gluon propagators that have been found by numerical calculation of the Schwinger· Dyson equations as well. as in lattice simulations. The existence of a gluon propagator that is finite at k 2 =O modifies substantially the transition between the phases with and without chiral symmetry.
126420285
Table 55 ; Measurement of the pseudorapidity and transverse momentum dependence of the elliptic flow of charged particles in lead-lead collisions at $\sqrt{s_{NN}}=2.76$ TeV with the ATLAS detector
120352716
Status and perspectives of the CAST experiment
The CERN Axion Solar Telescope (CAST) is currently the most sensitive axion helioscope designed to search for axions produced by the Primakoff process in the solar core. CAST is using a Large Hadron Collider (LHC) test magnet where axions could be converted into X-rays with energies up to 10 keV. During the phase I, the experiment operated with vacuum inside the magnet bores and covered axion masses up to 0.02 eV. In the phase II, the magnet bores were filled with a buffer gas (first 4He and later 3He) at various densities in order to extend the sensitivity to higher axion masses (up to f .18 eV). The phase II data taking was completed in 2011. So far, no evidence of axion signal has been found and CAST set the most restrictive experimental limit on the axion-photon coupling constant over a broad range of axion masses. The latest CAST results with 3He data in the mass range 0.39 eV < ma < 0.64 eV will be presented.
18585782
Compatibility of a model for the QCD-Pomeron and chiral-symmetry breaking phenomenologies
Abstract The phenomenology of a QCD-Pomeron model based on the exchange of a pair of non-perturbative gluons, i.e. gluon fields with a finite correlation length in the vacuum, is studied in comparison with the phenomenology of QCD chiral symmetry breaking, based on non-perturbative solutions of Schwinger-Dyson equations for the quark propagator including these non-perturbative gluon effects. We show that these models are incompatible, and point out some possibles origins of this problem.