152 research outputs found
String effects in Polyakov loop correlators
We compare the predictions of the effective string description of confinement
in finite temperature gauge theories to high precision Monte Carlo data for the
three-dimensional Z(2) gauge theory. We show that string interaction effects
become more relevant as the temperature is increased towards the deconfinement
one, and are well modeled by a Nambu-Goto string action.Comment: Lattice2002(nonzerot
Machine learning til realtidsforudsigelser af oprindelse-til-destination efterspørgsel for jernbaner med smart card og udbudsdata : Udvidet resumé
Realtidsforudsigelser af passagerefterspørgsel på jernbanen kan bidrage til smartere trafikstyring og på sigt til at udvikle et offentligt transportsystem som på forskellig vis imødekommer ekstraordinær efterspørgsel. Dette kræver adgang til detaljeret information om efterspørgselsmønstre i form af løbende indsamling af passagertal for hvert par af oprindelses- og destinationsstationer i korte tidsintervaller. I dette studie udvikles en machine learning model til forudsigelser af afvigelser fra det periodiske efterspørgselsmønster på Københavns S-bane i 15 minutters intervaller ved hjælp af realtidsdata fra Rejsekortet på efterspørgselssiden og Banedanmarks driftsstatistikker på udbudssiden. Studiet belyser dels betydningen af udbud for forudsigelse af efterspørgsel og dels udforskes måden hvorpå spatiotemporal data indlejres i modeller fra dyb læring for at opnå nøjagtige forudsigelser for mange-dimensionale og sparsomme data som disse
Some universal features of the effective string picture of pure gauge theories
The effective string describing the large distance behaviour of the quark
sources of gauge field theories in the confining phase in D=3 or D=4 space-time
dimensions can be formulated, in the infrared limit, as a suitable 2D conformal
field theory on surfaces with quark loops as boundaries. Recent results on
self-avoiding random surfaces allow to fix almost uniquely such a conformal
theory. As a consequence, some universal relationships among the string tension
, the thickness of the colour flux tube, the deconfinement temperature and a
lower bound of the glueball mass spectrum are found. The general agreement with
the data extracted from recent lattice simulations with different gauge groups
is rather impressive.(Talk held by F.Gliozzi at Lattice'92 , Amsterdam)Comment: 9 pages(LaTeX),DFTT61/9
Fluctuations, Saturation, and Diffractive Excitation in High Energy Collisions
Diffractive excitation is usually described by the Good--Walker formalism for
low masses, and by the triple-Regge formalism for high masses. In the
Good--Walker formalism the cross section is determined by the fluctuations in
the interaction. In this paper we show that by taking the fluctuations in the
BFKL ladder into account, it is possible to describe both low and high mass
excitation by the Good--Walker mechanism. In high energy collisions the
fluctuations are strongly suppressed by saturation, which implies that pomeron
exchange does not factorise between DIS and collisions. The Dipole Cascade
Model reproduces the expected triple-Regge form for the bare pomeron, and the
triple-pomeron coupling is estimated.Comment: 20 pages, 12 figure
Confining strings in SU(N) gauge theories
We calculate the string tensions of -strings in SU() gauge theories in
both 3 and 4 dimensions. In D=3+1, we find that the ratio of the string
tension to the fundamental string tension is consistent, at the level, with both the M(-theory)QCD-inspired conjecture and with
`Casimir scaling'. In D=2+1 we see a definite deviation from the MQCD formula,
as well as a much smaller but still significant deviation from Casimir scaling.
We find that in both D=2+1 and D=3+1 the high temperature spatial -string
tensions also satisfy approximate Casimir scaling. We point out that
approximate Casimir scaling arises naturally if the cross-section of the flux
tube is nearly independent of the flux carried, and that this will occur in an
effective dual superconducting description, if we are in the deep-London limit.
We estimate, numerically, the intrinsic width of -strings in D=2+1 and
indeed find little variation with . In addition to the stable -strings we
investigate some ofthe unstable strings, finding in D=2+1 that they satisfy
(approximate) Casimir scaling. We also investigate the basic assumption that
confining flux tubes are described by an effective string theory at large
distances. We estimate the coefficient of the universal L\"uscher correction
from periodic strings that are longer than 1 fermi, and find in
D=3+1 and in D=2+1. These values are within of the
simple bosonic string values and are inconsistent with other simple effective
string theories.Comment: 57 pages, 11 figures. Errors on fits reduced by altering the analysis
to a standard one. Conclusions unchanged; note addedchanged. Some typos
correcte
Lattice calculation of hybrid mesons with improved Kogut-Susskind fermions
We report on a lattice determination of the mass of the exotic
hybrid meson using an improved Kogut-Susskind action. Results from both
quenched and dynamical quark simulations are presented. We also compare with
earlier results using Wilson quarks at heavier quark masses. The results on
lattices with three flavors of dynamical quarks show effects of sea quarks on
the hybrid propagators which probably result from coupling to two meson states.
We extrapolate the quenched results to the physical light quark mass to allow
comparison with experimental candidates for the hybrid meson. The
lattice result remains somewhat heavier than the experimental result, although
it may be consistent with the .Comment: 24 pages, 12 figures. Replaced to match published versio
Elastic and quasi-elastic and scattering in the Dipole Model
We have in earlier papers presented an extension of Mueller's dipole cascade
model, which includes sub-leading effects from energy conservation and running
coupling as well as colour suppressed saturation effects from pomeron loops via
a ``dipole swing''. The model was applied to describe the total and diffractive
cross sections in and collisions, and also the elastic cross
section in scattering.
In this paper we extend the model to describe the corresponding quasi-elastic
cross sections in , namely the exclusive production of vector mesons
and deeply virtual compton scattering. Also for these reactions we find a good
agrement with measured cross sections. In addition we obtain a reasonable
description of the -dependence of the elastic and quasi-elastic
cross sections
Extracting the Distribution Amplitudes of the rho meson from the Color Glass Condensate
We extract the leading twist-2 and subleading twist-3 Distribution Amplitudes
(DAs) of the rho meson using the HERA data on diffractive rho photoproduction.
We do so using several Colour Glass Condensate (CGC) inspired and a Regge
inspired dipole models. We find that our extracted twist-2 DA is not much model
dependent and is consistent with QCD Sum Rules and lattice predictions. The
extracted twist-3 DA is more model dependent but is still consistent with the
Sum Rules prediction.Comment: 21 pages, 10 figures, 3 tables. Section 6 revised, figures 8 and 9
and table 3 updated. Conclusions essentially unchange
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