4,928 research outputs found
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
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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.
Experimental observation of the X-shaped near field spatio-temporal correlation of ultra-broadband twin beams
In this work we present the experimental observation of the non factorable
near field spatio-temporal correlation of ultra-broadband twin beams generated
by parametric down conversion (PDC), in an interferometric-type experiment
using sum frequency generation, where both the temporal and spatial degrees of
freedom of PDC light are controlled with very high resolution. The revealed
X-structure of the correlation is in accordance with the predictions of the
theory.Comment: 5 pages, 3 figure
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
Heavy Quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature
We calculate the heavy quarkonium energy levels and decay widths in a
quark-gluon plasma, whose temperature T and screening mass m_D satisfy the
hierarchy m alpha_s >> T >> m alpha_s^2 >> m_D (m being the heavy-quark mass),
at order m alpha_s^5. We first sequentially integrate out the scales m, m
alpha_s and T, and, next, we carry out the calculations in the resulting
effective theory using techniques of integration by regions. A collinear region
is identified, which contributes at this order. We also discuss the
implications of our results concerning heavy quarkonium suppression in heavy
ion collisions.Comment: 25 pages, 2 figure
Bethe--Salpeter equation in QCD
We extend to regular QCD the derivation of a confining
Bethe--Salpeter equation previously given for the simplest model of scalar QCD
in which quarks are treated as spinless particles. We start from the same
assumptions on the Wilson loop integral already adopted in the derivation of a
semirelativistic heavy quark potential. We show that, by standard
approximations, an effective meson squared mass operator can be obtained from
our BS kernel and that, from this, by expansion the
corresponding Wilson loop potential can be reobtained, spin--dependent and
velocity--dependent terms included. We also show that, on the contrary,
neglecting spin--dependent terms, relativistic flux tube model is reproduced.Comment: 23 pages, revte
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