4,697 research outputs found
The 1P quarkonium fine splittings at NLO
We calculate the 1P heavy quarkonium fine splittings at NLO and discuss the
impact of the calculation on the chi_b(1P) splittings.Comment: 10 pages, 3 figure
Effective Field Theories for Heavy Quarkonium
We briefly review how nonrelativistic effective field theories give us a
definition of the QCD potentials and a coherent field theory derived quantum
mechanical scheme to calculate the properties of bound states made by two or
more heavy quarks. In this framework heavy quarkonium properties depend only on
the QCD parameters (quark masses and \als) and nonpotential corrections are
systematically accounted for. The relation between the form of the
nonperturbative potentials and the low energy QCD dynamics is also discussed.Comment: Invited Plenary talk at The 20th European Conference on Few-Body
Problems in Physics. September 10-14 2007. Pisa, Italy. To be published on
Few-Body System
Dimensionality of the spatio-temporal entanglement of PDC photon pairs
In this work the Schmidt number of the two-photon state generated by
parametric-down conversion (PDC) is evaluated in the framework of a fully
spatio-temporal model for PDC. A comparison with the results obtained in either
purely spatial or purely temporal models shows that the degree of entanglement
of the PDC state cannot be trivially reduced to the product of the Schmidt
numbers obtained in models with lower dimensionality, unless the detected
bandwidth is very narrow. This result is a consequence of the non-factorability
of the state in the spatial and temporal degrees of freedoms of twin photons.
In the limit of a broad pump beam, we provide a geometrical interpretation of
the Schmidt number, as the ratio between the volume of the phase matching
region and of a correlation volume.Comment: 17 pages, 10 figures. Submitted to Phys. Rev.
Brambilla et al. Reply to a Comment by J. Reinhardt et al. on "Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition"
G. Brambilla et al. Reply to a Comment by J. Reinhardt et al. questioning the
existence of equilibrium dynamics above the critical volume fraction of
colloidal hard spheres predicted by mode coupling theory.Comment: To appear in Phys. Rev. Lett. Reply to a Comment by J. Reinhardt et
al. (see arXiv:1010.2891), which questions the existence of equilibrium
dynamics above the critical volume fraction of glassy colloidal hard spheres
predicted by mode coupling theor
The QCD Potential at
Within an effective field theory framework, we obtain an expression for the
next-to-leading term in the expansion of the singlet QCD
potential in terms of Wilson loops, which holds beyond perturbation theory. The
ambiguities in the definition of the QCD potential beyond leading order in
are discussed and a specific expression for the potential is given.
We explicitly evaluate this expression at one loop and compare the outcome with
the existing perturbative results. On general grounds we show that for quenched
QED and fully Abelian-like models this expression exactly vanishes.Comment: 19 pages, LaTeX, 1 figure. Journal version. Discussion refined,
misprints corrected, few references added; results unchange
The three-quark static potential in perturbation theory
We study the three-quark static potential in perturbation theory in QCD. A
complete next-to-leading order calculation is performed in the singlet, octets
and decuplet channels and the potential exponentiation is demonstrated. The
mixing of the octet representations is calculated. At next-to-next-to-leading
order, the subset of diagrams producing three-body forces is identified in
Coulomb gauge and its contribution to the potential calculated. Combining it
with the contribution of the two-body forces, which may be extracted from the
quark-antiquark static potential, we obtain the complete
next-to-next-to-leading order three-quark static potential in the
colour-singlet channel.Comment: 36 pages, 11 figures, version published in Phys.Rev.
Poincare' invariance and the heavy-quark potential
We derive and discuss the constraints induced by Poincare' invariance on the
form of the heavy-quark potential up to order 1/m^2. We present two
derivations: one uses general arguments directly based on the Poincare' algebra
and the other follows from an explicit calculation on the expression of the
potential in terms of Wilson loops. We confirm relations from the literature,
but also clarify the origin of a long-standing false statement pointed out
recently.Comment: 20 pages, 4 figure
BANK EROSION AND INSTABILITY MONITORING WITH A LOW COST TERRESTRIAL LASER SCANNER
ABSTRACT: Among the dominant processes taking place in a river basin, especially mountain ones, sediments
creation and transport play a key role in morphological processes. Studies usually focus on big mass movements,
such as landslides and debris flows, or on wide spread slope erosion due to rainfalls, while bank erosion is
neglected or not considered essential for sediment budget at basin scale. Nevertheless, authors consider bank
erosion a process that deserve more careful studies; not only the sediment share from bank erosion is not
negligible in steep mountain rivers, but also the process can threat structures on river sides due the possibility to
have limited, but still significant, mass collapse of bank sections during intense events. The paper present an
attempt to monitor bank erosion in a section of a river in Northern Italy Alps and to put it in relation with
weather and water discharge. Survey campaign was set up at regular time intervals, or after particularly intense
rainfalls, and uses a Terrestrial Laser Scanner (TLS) to acquire the bank surface. The tool was developed
internally, at Politecnico di Milano, to meet requirements about low cost level and good accuracy. Successive
acquisitions of point clouds were elaborated, via an ad-hoc MatLab code, to determine erosion, or deposition,
volumes of sediments. These volumetric results have been evaluated in relation with rainfalls and freeze-thaw
cycles looking for a relationship between environmental conditions and bank failures. Some interesting results
are shown, such as a relation between erosion rates and temperature or water flow in the river. The path to a
complete process understanding and modelling is long, however the results reported can be considered a first
step towards objective
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