414 research outputs found
Short distance physics with heavy quark potentials
We present lattice studies of heavy quark potentials in the quenched
approximation of QCD at finite temperatures. Both, the color singlet and color
averaged potentials are calculated. While the potentials are well known at
large distances, we give a detailed analysis of their short distance behavior
(from 0.015 fm to 1 fm) near the critical temperature. At these distances we
expect that the T-dependent potentials go over into the zero temperature
potential. Indeed, we find evidences that the temperature influence gets
suppressed and the potentials starts to become a unique function of the
underlying distance scale. We use this feature to normalize the heavy quark
potentials at short distances and extract the free energy of the quark system
in a gluonic heat bath.Comment: Lattice2001(hightemp), 3 pages, 2 figure
An important fingerprint of wildfires on the European aerosol load
Abstract. Wildland fires represent the major source of fine aerosols, i.e., atmospheric particles with diameters <1 μm. The largest numbers of these fires occur in Africa, Asia and South America, but a not negligible fraction also occurs in Eastern Europe and former USSR countries, particularly in the Russian Federation, Ukraine and Kazakhstan. Besides the impact of large forest fires, recent studies also highlighted the crucial role played by routine agricultural fires in Eastern Europe and Russia on the Arctic atmosphere. An evaluation of the impact of these fires over Europe is currently not available. The assessment of the relative contribution of fires to the European aerosol burden is hampered by the complex mixing of natural and anthropogenic particle types across the continent. In this study we use long term (2002–2007) satellite-based fires and aerosol data coupled to atmospheric trajectory modelling in the attempt to estimate the wildfires contribution to the European aerosol optical thickness (AOT). Based on this dataset, we provide evidence that fires-related aerosols play a major role in shaping the AOT yearly cycle at the continental scale. In general, the regions most impacted by wildfires emissions and/or transport are Eastern and Central Europe as well as Scandinavia. Conversely, a minor impact is found in Western Europe and in the Western Mediterranean. We estimate that in spring 5 to 35% of the European fine fraction AOT (FFAOT) is attributable to wildland fires. The estimated impact maximizes in April (20–35%) in Eastern and Central Europe as well as in Scandinavia and in the Central Mediterranean. An important contribution of wildfires to the FFAOT is also found in summer over most of the continent, particularly in August over Eastern Europe (28%) and the Mediterranean regions, from Turkey (34%) to the Western Mediterranean (25%). Although preliminary, our results suggest that this fires-related, continent-wide haze plays a not negligible role on the European radiation budget, and possibly, on the European air quality, therefore representing a clear target for mitigation
Screening in Hot SU(2) Gauge Theory and Propagators in 3d Adjoint Higgs model
We investigate the large distance behavior of the electric and magnetic
propagators of hot SU(2) gauge theory in different gauges using lattice
simulations of the full 4d theory and the effective, dimensionally reduced 3d
theory. A comparison of the 3d and 4d data for the propagators suggests that
dimensional reduction works surprisingly well down to temperatures T=2 T_c. A
detailed study of the volume dependence of magnetic propagators is performed.
The electric propagators show exponential decay at large distances in all
gauges considered and a possible gauge dependence of the electric screening
mass turns out to be statistically insignificant.Comment: Submitted to Proceedings of Lattice 2000 and Workshop "Strong and
Electroweak Matter 2000". LaTeX uses espcrc2.st
Scaling, asymptotic scaling and Symanzik improvement. Deconfinement temperature in SU(2) pure gauge theory
We report on a high statistics simulation of SU(2) pure gauge field theory at
finite temperature, using Symanzik action. We determine the critical coupling
for the deconfinement phase transition on lattices up to 8 x 24, using Finite
Size Scaling techniques. We find that the pattern of asymptotic scaling
violation is essentially the same as the one observed with conventional, not
improved action. On the other hand, the use of effective couplings defined in
terms of plaquette expectation values shows a precocious scaling, with respect
to an analogous analysis of data obtained by the use of Wilson action, which we
interpret as an effect of improvement.Comment: 43 pages ( REVTeX 3.0, self-extracting shell archive, 13 PostScript
figs.), report IFUP-TH 21/93 (2 TYPOS IN FORMULAS CORRECTED,1 CITATION
UPDATED,CITATIONS IN TEXT ADDED
Remarks on a class of renormalizable interpolating gauges
A class of covariant gauges allowing one to interpolate between the Landau,
the maximal Abelian, the linear covariant and the Curci-Ferrari gauges is
discussed. Multiplicative renormalizability is proven to all orders by means of
algebraic renormalization. All one-loop anomalous dimensions of the fields and
gauge parameters are explicitly evaluated in the MSbar scheme.Comment: 24 pages. no figure
An analytic study of the off-diagonal mass generation for Yang-Mills theories in the maximal Abelian gauge
We investigate a dynamical mass generation mechanism for the off-diagonal
gluons and ghosts in SU(N) Yang-Mills theories, quantized in the maximal
Abelian gauge. Such a mass can be seen as evidence for the Abelian dominance in
that gauge. It originates from the condensation of a mixed gluon-ghost operator
of mass dimension two, which lowers the vacuum energy. We construct an
effective potential for this operator by a combined use of the local composite
operators technique with the algebraic renormalization and we discuss the gauge
parameter independence of the results. We also show that it is possible to
connect the vacuum energy, due to the mass dimension two condensate discussed
here, with the non-trivial vacuum energy originating from the condensate ,
which has attracted much attention in the Landau gauge.Comment: 24 pages, 2 .eps figures. v2: version accepted for publication in
Phys.Rev.
Strong Coupling Constant from Scaling Violations in Fragmentation Functions
We present a new determination of the strong coupling constant alpha_s
through the scaling violations in the fragmentation functions for charged
pions, charged kaons, and protons. In our fit we include the latest e+e-
annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and
older, yet very precise data from SLAC PEP at center-of-mass energy sqrt(s)=29
GeV. A new world average of alpha_s is given.Comment: 10 pages, 3 eps figue
Dynamical mass generation in quantum field theory : some methods with application to the Gross-Neveu model and Yang-Mills theory
We introduce some techniques to investigate dynamical mass generation. The
Gross-Neveu model (GN) is used as a toy model, because the GN mass gap is
exactly known, making it possible to check reliability of the various methods.
Very accurate results are obtained. Also application to SU(N) Yang-Mills (YM)
is discussed.Comment: 8 LaTeX2e pages, uses Kluwer class file crckbked.cls. Kluwer package
included. To appear in: Proceedings of the NATO Advanced Research Workshop on
"Confinement, Topology, and other Non-Perturbative Aspects of QCD", Stara
Lesna, Slovakia, 21-27 jan 200
On parton distributions beyond the leading order
The importance of properly taking into account the factorization scheme
dependence of parton distribution functions is emphasized. A serious error in
the usual handling of this topic is pointed out and the correct procedure for
transforming parton distribution functions from one factorisation scheme to
another recalled. It is shown that the conventional and
DIS definitions thereof are ill-defined due to the lack of distinction between
the factorisation scheme dependence of parton distribution functions and
renormalisation scheme dependence of the strong coupling constant . A
novel definition of parton distribution functions is suggested and its role in
the construction of consistent next-to-leading order event generators briefly
outlined.Comment: PRA-HEP-93/05, Latex, 10 pages and 2 Postscript figures appended at
the end of this fil
Renormalizing a BRST-invariant composite operator of mass dimension 2 in Yang-Mills theory
We discuss the renormalization of a BRST and anti-BRST invariant composite
operator of mass dimension 2 in Yang-Mills theory with the general BRST and
anti-BRST invariant gauge fixing term of the Lorentz type. The interest of this
study stems from a recent claim that the non-vanishing vacuum condensate of the
composite operator in question can be an origin of mass gap and quark
confinement in any manifestly covariant gauge, as proposed by one of the
authors. First, we obtain the renormalization group flow of the Yang-Mills
theory. Next, we show the multiplicative renormalizability of the composite
operator and that the BRST and anti-BRST invariance of the bare composite
operator is preserved under the renormalization. Third, we perform the operator
product expansion of the gluon and ghost propagators and obtain the Wilson
coefficient corresponding to the vacuum condensate of mass dimension 2.
Finally, we discuss the connection of this work with the previous works and
argue the physical implications of the obtained results.Comment: 49 pages, 35 eps-files, A number of typographic errors are corrected.
A paragraph is added in the beginning of section 5.3. Two equations (7.1) and
(7.2) are added. A version to be published in Phys. Rev.
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