512 research outputs found
Nuclear models on a lattice
We present the first results of a quantum field approach to nuclear models
obtained by lattice techniques. Renormalization effects for fermion mass and
coupling constant in case of scalar and pseudoscalar interaction lagrangian
densities are discussed.Comment: 4 pages - 7 figures ; Invited talk to QCD 05: 12th International QCD
Conference, 4-9 Jul 2005, Montpellier, France ; To appear in Nucl. Phys. B
(Proc. Suppl.
Remarks on sum rules in the heavy quark limit of QCD
We underline a problem existing in the heavy quark limit of QCD concerning
the rates of semileptonic B decays into P-wave mesons, where (wide states) or (narrow states). The leading order
sum rules of Bjorken and Uraltsev suggest , in contradiction with experiment. The same trend follows also from a sum
rule for the subleading curent matrix element correction .
The problem is made explicit in relativistic quarks models \`a la Bakamjian and
Thomas, that give a transparent physical interpretation of the latter as due,
not to a force, but to the Wigner rotation of the light quark spin.
We point out moreover that the selection rule for decay constants of states, , predicts, assuming the model of factorization,
the opposite hierarchy .Comment: Contribution to the International Europhysics Conference on HEP,
Budapest, July 2001 (presented by L. Oliver); 5 page
Instanton traces in lattice gluon correlation functions
Strong coupling constant computed in Landau gauge and MOM renormalization
scheme from lattice two and three gluon Green Functions exhibits an unexpected
behavior in the deep IR, showing a maximum value around . We
analise this coupling below this maximum within a semiclassical approach, were
gluon degrees of freedom at very low energies are described in terms of the
classical solutions of the lagrangian, namely instantons. We provide some new
results concerning the relationship between instantons and the low energy
dynamics of QCD, by analising gluon two- and three-point Green functions
separately and with the help of a cooling procedure to eliminate short range
correlations.Comment: 4 pages, talk given at XXXX Rencontres de Moriond on QCD and Hadronic
Interactions, La Thuile (Italy
B_s-\bar{B_s} mixing with a chiral light quark action
We study the mixing amplitude in Standard Model by
computing the relevant hadronic matrix element in the static limit of lattice
HQET with the Neuberger light quark action. In the quenched approximation, and
after matching to the scheme in QCD, we obtain .Comment: 6 pages, 3 figures, talk presented at Lattice 2005 (Heavy quark
physics
The Infrared Behaviour of the Pure Yang-Mills Green Functions
We study the infrared behaviour of the pure Yang-Mills correlators using
relations that are well defined in the non-perturbative domain. These are the
Slavnov-Taylor identity for three-gluon vertex and the Schwinger-Dyson equation
for ghost propagator in the Landau gauge. We also use several inputs from
lattice simulations. We show that lattice data are in serious conflict with a
widely spread analytical relation between the gluon and ghost infrared critical
exponents. We conjecture that this is explained by a singular behaviour of the
ghost-ghost-gluon vertex function in the infrared. We show that, anyhow, this
discrepancy is not due to some lattice artefact since lattice Green functions
satisfy the ghost propagator Schwinger-Dyson equation. We also report on a
puzzle concerning the infrared gluon propagator: lattice data seem to favor a
constant non vanishing zero momentum gluon propagator, while the Slavnov-Taylor
identity (complemented with some regularity hypothesis of scalar functions)
implies that it should diverge.Comment: 25 pages, 7 figures; replaced version with some references adde and
an enlarged discussion of the non-renormalization theorem; second replacement
with improved figures and added reference
Asymptotic behavior of the ghost propagator in SU3 lattice gauge theory
We study the asymptotic behavior of the ghost propagator in the quenched
SU(3) lattice gauge theory with Wilson action. The study is performed on
lattices with a physical volume fixed around 1.6 fm and different lattice
spacings: 0.100 fm, 0.070 fm and 0.055 fm. We implement an efficient algorithm
for computing the Faddeev-Popov operator on the lattice. We are able to
extrapolate the lattice data for the ghost propagator towards the continuum and
to show that the extrapolated data on each lattice can be described up to
four-loop perturbation theory from 2.0 GeV to 6.0 GeV. The three-loop values
are consistent with those extracted from previous perturbative studies of the
gluon propagator. However the effective \Lambda_{\ms} scale which reproduces
the data does depend strongly upon the order of perturbation theory and on the
renormalization scheme used in the parametrization. We show how the truncation
of the perturbative series can account for the magnitude of the dependency in
this energy range. The contribution of non-perturbative corrections will be
discussed elsewhere.Comment: 26 pages, 7 figure
Three-loop beta function and non-perturbative in asymmetric momentum scheme
We determine the three-loop coefficient of the beta function in the
asymmetric momentum subtraction scheme in Landau gauge. This scheme is
convenient for lattice studies of \alpha_s, the running coupling constant of
QCD. We present high statistics lattice results for \alpha_s in the SU(3)
Yang-Mills theory without quark, compare with the three-loop running and
extract the value of the corresponding \Lambda_\msbar parameter. We estimate
the systematic error coming from four-loop terms. We obtain the result:
\Lambda_\msbar = 295 (5) (15) {a^{-1}(\beta=6.0) \over 1.97 GeV} MeV.Comment: 9 pages, LaTeX with two figures. The final analysis has been
revisited to include an estimation of the systematic error coming from
higher-order term
Indirect lattice evidence for the Refined Gribov-Zwanziger formalism and the gluon condensate in the Landau gauge
We consider the gluon propagator 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
. Including this effect allows to obtain an acceptable fit up to
1 \'{a} 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 . As a byproduct, we can
also provide the prediction obtained at
the renormalization scale .Comment: 17 pages, 10 figures, updated version, accepted for publication in
Phs.Rev.
Drake Antarctic Agile Meteor Radar (DrAAMER) First Results: Configuration and Comparison of Mean and Tidal Wind and Gravity Wave Momentum Flux Measurements with SAAMER
A new-generation meteor radar was installed at the Brazilian Antarctic Comandante Ferraz Base (62.1degS) in March 2010. This paper describes the motivations for the radar location, its measurement capabilities, and comparisons of measured mean winds, tides, and gravity wave momentum fluxes from April to June of 2010 and 2011 with those by a similar radar on Tierra del Fuego (53.8degS). Motivations for the radars include the "hotspot" of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere (MLT) centered over the Drake Passage, the maximum of the semidiurnal tide at these latitudes, and the lack of other MLT wind measurements in this latitude band. Mean winds are seen to be strongly modulated at planetary wave and longer periods and to exhibit strong coherence over the two radars at shorter time scales as well as systematic seasonal variations. The semidiurnal tide contribute most to the large-scale winds over both radars, with maximum tidal amplitudes during May and maxima at the highest altitudes varying from approx.20 to >70 m/s. In contrast, the diurnal tide and various planetary waves achieve maximum winds of approx.10 to 20 m/s. Monthly-mean gravity wave momentum fluxes appear to reflect the occurrence of significant sources at lower altitudes, with relatively small zonal fluxes over both radars, but with significant, and opposite, meridional momentum fluxes below approx.85 km. These suggest gravity waves propagating away from the Drake Passage at both sites, and may indicate an important source region accounting in part for this "hotspot"
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