57 research outputs found
Extracting infrared QCD coupling from meson spectrum
In the framework of the Bethe-Salpeter formalism used in previous papers to
evaluate the quarkonium spectrum, here we reverse the point of view to extract
an ``experimental'' running coupling alpha_s(Q^2) in the infrared (IR) region
from the data. The values so obtained agree within the errors with the
Shirkov-Solovtsov analytic coupling for 200 MeV <Q< 1.2 GeV, thus giving a very
satisfactory unifying description of high and low energy phenomena. Below 1 GeV
however alpha_s(Q^2) seems to vanish as Q to 0. The paper is based on a work in
progress in collaboration with D.V.Shirkov.Comment: Talk given at 7th International Conference on Quark Confinement and
the Hadron Spectrum, Azores - Portugal, 2-7 Sep 2006. To be published in AIP
Conf.Pro
Extreme summer temperatures in Western Europe
Abstract. We discuss the evolution of summer temperature extremes over Western Europe during 1961–2004 in the context of current climate warming. Using a parametric approach, we investigate the role of properties and changes in probability density functions of daily temperatures in modifying the frequency of severe, isolated events. In this perspective, the recent intensification of extremely warm events over Europe turns out to be well consistent with a pure, nonuniform shift of mean values, with no room for conjectures about increasing temperature variability
1961–1990 monthly high-resolution solar radiation climatologies for Italy
Abstract. We present a methodology for estimating solar radiation climatologies from a sparse network of global radiation and/or sunshine duration records: it allows to obtain high-resolution grids of monthly normal values for global radiation (and for the direct and diffuse components), atmospheric turbidity, and surface absorbed radiation. We discuss the application of the methodology to a preliminary version of an Italian global radiation and sunshine duration data set, which completion is still in progress and present the resulting 1961–1990 monthly radiation climatologies
Estimating local records for Northern and Central Italy from a sparse secular temperature network and from 1961–1990 climatologies
The paper presents monthly 30-arc-second-resolution Northern and Central Italy temperature climatologies and discusses the procedure we adopt to superimpose the information of temperature secular records onto these climatologies. The climatologies are obtained by means of a step-wise linear regression method which aims at determining the temperature dependence on geographical and morphological variables. Such a method is applied to a database of about 800 monthly 1961&ndash;1990 temperature normals. In the first regression (temperature vs. elevation) the recorded data are considered; the further regressions concern the residuals obtained after taking into account the effect of each variable, in order of importance. An estimated secular anomaly record can be obtained for each point of the climatology grid by means of a distance-weighted average of the temperature anomaly records of the stations surrounding the grid point
High-resolution analysis of 1 day extreme precipitation in Sicily
Sicily, a major Mediterranean island, has experienced several exceptional precipitation episodes and floods during the last century, with serious damage to human life and the environment. Long-term, rational planning of urban development is indispensable to protect the population and to avoid huge economic losses in the future. This requires a thorough knowledge of the distributional features of extreme precipitation over the complex territory of Sicily. In this study, we perform a detailed investigation of observed 1 day precipitation extremes and their frequency distribution, based on a dense data set of high-quality, homogenized station records in 1921-2005. We estimate very high quantiles (return levels) corresponding to 10-, 50-and 100-year return periods, as predicted by a generalized extreme value distribution. Return level estimates are produced on a regular high-resolution grid (30 arcsec) using a variant of regional frequency analysis combined with regression techniques. Results clearly reflect the complexity of this region, and show the high vulnerability of its eastern and northeastern parts as those prone to the most intense and potentially damaging events
Bound state approach to the QCD coupling at low energy scales
We exploit theoretical results on the meson spectrum within the framework of
a Bethe-Salpeter (BS) formalism adjusted for QCD, in order to extract an
``experimental'' coupling \alpha_s^{exp}(Q^2) below 1 GeV by comparison with
the data. Our results for \alpha_s^{exp}(Q^2) exhibit a good agreement with the
infrared safe Analytic Perturbation Theory (APT) coupling from 1 GeV down to
200 MeV. As a main result, we claim that the combined BS-APT theoretical scheme
provides us with a rather satisfactory correlated understanding of very high
and low energy phenomena.Comment: Revised version, to appear on Physical Review Letters. 7 pages, 2
figures, Revte
The Bjorken sum rule with Monte Carlo and Neural Network techniques
Determinations of structure functions and parton distribution functions have
been recently obtained using Monte Carlo methods and neural networks as
universal, unbiased interpolants for the unknown functional dependence. In this
work the same methods are applied to obtain a parametrization of polarized Deep
Inelastic Scattering (DIS) structure functions. The Monte Carlo approach
provides a bias--free determination of the probability measure in the space of
structure functions, while retaining all the information on experimental errors
and correlations. In particular the error on the data is propagated into an
error on the structure functions that has a clear statistical meaning. We
present the application of this method to the parametrization from polarized
DIS data of the photon asymmetries and from which we determine
the structure functions and , and discuss the
possibility to extract physical parameters from these parametrizations. This
work can be used as a starting point for the determination of polarized parton
distributions.Comment: 24 pages, 6 figure
QCD coupling below 1 GeV from quarkonium spectrum
In this paper we extend the work synthetically presented in Ref.[1] and give
theoretical details and complete tables of numerical results. We exploit
calculations within a Bethe-Salpeter (BS) formalism adjusted for QCD, in order
to extract an ``experimental'' strong coupling \alpha_s^{exp}(Q^2) below 1 GeV
by comparison with the meson spectrum. The BS potential follows from a proper
ansatz on the Wilson loop to encode confinement and is the sum of a
one-gluon-exchange and a confinement terms. Besides, the common perturbative
strong coupling is replaced by the ghost-free expression \alpha_E(Q^2)
according to the prescription of Analytic Perturbation Theory (APT). The
agreement of \alpha_s^{exp}(Q^2) with the APT coupling \alpha_E(Q^2) turns out
to be reasonable from 1 GeV down to the 200 MeV scale, thus confirming
quantitatively the validity of the APT prescription. Below this scale, the
experimental points could give a hint on the vanishing of \alpha_s(Q^2) as Q
approaches zero. This infrared behaviour would be consistent with some lattice
results and a ``massive'' generalization of the APT approach. As a main result,
we claim that the combined BS-APT theoretical scheme provides us with a rather
satisfactory correlated understanding of very high and rather low energy
phenomena from few hundreds MeV to few hundreds GeV.Comment: Preliminary revision. Typos corrected, comments and references adde
QCDMAPT: program package for Analytic approach to QCD
A program package, which facilitates computations in the framework of
Analytic approach to QCD, is developed and described in details. The package
includes the explicit expressions for relevant spectral functions calculated up
to the four-loop level and the subroutines for necessary integrals.Comment: 18 pages, 4 figures; QCDMAPT package is available from
http://cpc.cs.qub.ac.uk/summaries/AEGP_v1_0.htm
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