94 research outputs found
Lattice simulations for the running coupling constant of QCD
The strong coupling constant alpha_s(mu_0), taken at a fixed reference scale
mu_0, is the single free parameter of QCD and should be known to the highest
available precision. The value of alpha_s should also be determined with good
accuracy over as large a range of scales as possible, in order to reveal
potential anomalous running in the strength of the strong interaction. Lattice
QCD is now able to calculate alpha_s with accuracy comparable to or better than
experiment. We review the status of such lattice calculations in quenched and
full QCD.Comment: 10 pages; invited seminar presented at the VIII International
Workshop on Hadron Physics 2002, Bento Goncalves RS, Brazil, April 14-19,
200
Lattice Results in Coulomb Gauge
We discuss recent numerical results obtained for gluon and ghost propagators
in lattice Coulomb gauge and the status of the so-called Gribov-Zwanziger
confinement scenario in this gauge. Particular emphasis will be given to the
eigenvalue spectrum of the Faddeev-Popov matrix.Comment: 7 pages; plenary talk presented at the QCHS7, Ponta Delgada Acores -
Portugal (September 2006
How to extract information from Green's functions in Landau gauge
The infrared behavior of gluon and ghost propagators offers a crucial test of
confinement scenarios in Yang-Mills theories. A nonperturbative study of these
propagators from first principles is possible in lattice simulations, but one
must consider significantly large lattice sizes in order to approach the
infrared limit. We propose constraints based on general properties of the
propagators to gain control over the extrapolation of data to the
infinite-volume limit. These bounds also provide a way to relate the
propagators to simpler, more intuitive quantities. We apply our analysis to the
case of pure SU(2) gauge theory in Landau gauge, using the largest lattice
sizes to date. Our results seem to contradict commonly accepted confinement
scenarios. We argue that it is not so.Comment: 6 pages, proceedings of SPMTP08 (Dubna, June 2008), talk presented by
A. Cucchier
Discretization effects and gauge independence for the electric and magnetic screening masses
We evaluate the electric and magnetic screening masses from the long-distance
behavior of the (temporal and spatial) gluon correlation functions, for pure
SU(2) gauge theory at finite temperature. In order to investigate the gauge
dependence of the screening masses we consider seven different gauges. We also
evaluate these masses using different definitions of the lattice gluon field,
corresponding to discretization errors of different orders.Comment: LATTICE99(finite temperature
Numerical Simulation of N-vector Spin Models in a Magnetic Field
Three-dimensional N-vector spin models may define universality classes for
such diverse phenomena as i) the superfluid transition in liquid helium
(currently investigated in the micro-gravity environment of the Space Shuttle)
and ii) the transition from hadronic matter to a quark-gluon plasma, studied in
heavy-ion collisions at the laboratories of Brookhaven and CERN. The models
have been extensively studied both by field-theoretical and by statistical
mechanical methods, including Monte Carlo simulations using cluster algorithms.
These algorithms are applicable also in the presence of a magnetic field. Key
quantities for the description of the transitions above -- such as universal
critical amplitude ratios and the location of the so-called pseudo-critical
line -- can be obtained from the models' magnetic equation of state, which
relates magnetization, external magnetic field and temperature. Here we present
an improved parametrization for the equation of state of the models, allowing a
better fit to the numerical data. Our proposed form is inspired by perturbation
theory, with coefficients determined nonperturbatively from fits to the data.Comment: 6 pages, 2 figures. Work presented at the IV Brazilian Meeting on
Simulational Physics -- Ouro Preto - MG/Brazil, August 200
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