20,306 research outputs found
Two-loop Improved Truncation of the Ghost-Gluon Dyson-Schwinger Equations: Multiplicatively Renormalizable Propagators and Nonperturbative Running Coupling
The coupled Dyson-Schwinger equations for the gluon and ghost propagators are
investigated in the Landau gauge using a two-loop improved truncation that
preserves the multiplicative renormalizability of the propagators. In this
truncation all diagrams contribute to the leading order infrared analysis. The
infrared contributions of the nonperturbative two-loop diagrams to the gluon
vacuum polarization are computed analytically, and this reveals that infrared
power behaved propagator solutions only exist when the squint diagram
contribution is taken into account. For small momenta the gluon and ghost
dressing functions behave respectively like (p^2)^{2\kappa} and
(p^2)^{-\kappa}, and the running coupling exhibits a fixed point. The values of
the infrared exponent and fixed point depend on the precise details of the
truncation. The coupled ghost-gluon system is solved numerically for all
momenta, and the solutions have infrared behaviors consistent with the
predictions of the infrared analysis. For truncation parameters chosen such
that \kappa=0.5, the two-loop improved truncation is able to produce solutions
for the propagators and running coupling which are in very good agreement with
recent lattice simulations.Comment: 41 pages, LateX; minor corrections; accepted for publication in
Few-Body System
Comment on "Nucleon form factors and a nonpointlike diquark"
Authors of Phys. Rev. C 60, 062201 (1999) presented a calculation of the
electromagnetic form factors of the nucleon using a diquark ansatz in the
relativistic three-quark Faddeev equations. In this Comment it is pointed out
that the calculations of these form factors stem from a three-quark bound state
current that contains overcounted contributions. The corrected expression for
the three-quark bound state current is derived.Comment: 6 pages, 1 figure, revtex, eps
Strongly Secure Communications Over the Two-Way Wiretap Channel
We consider the problem of secure communications over the two-way wiretap
channel under a strong secrecy criterion. We improve existing results by
developing an achievable region based on strategies that exploit both the
interference at the eavesdropper's terminal and cooperation between legitimate
users. We leverage the notion of channel resolvability for the multiple-access
channel to analyze cooperative jamming and we show that the artificial noise
created by cooperative jamming induces a source of common randomness that can
be used for secret-key agreement. We illustrate the gain provided by this
coding technique in the case of the Gaussian two-way wiretap channel, and we
show significant improvements for some channel configurations.Comment: 11 pages, 7 figures, submitted to IEEE Transactions on Information
Forensics and Security, Special Issue: "Using the Physical Layer for Securing
the Next Generation of Communication Systems
Method and apparatus for fabricating improved solar cell modules
A method and apparatus for fabricating an improved solar cell module is described. The apparatus includes a supply drum for feeding a flexible strip having etched electrical circuitry deposited on it a supply drum for feeding into overlying engagement with the flexible strip a flexible tape having a pair of exposed tacky surfaces, and a plurality of rams for receiving and depositing a plurality of solar cells in side-by-side relation on an exposed tacky surface of the tape in electrical contacting engagement with the etched circuitry
Detection of Spiral photons in Quantum Optics
We show that a new type of photon detector, sensitive to the gradients of
electromagnetic fields, should be a useful tool to characterize the quantum
properties of spatially-dependent optical fields. As a simple detector of such
a kind, we propose using magnetic dipole or electric quadrupole transitions in
atoms or molecules and apply it to the detection of spiral photons in
Laguerre-Gauss (LG) beams. We show that LG beams are not true hollow beams, due
to the presence of magnetic fields and gradients of electric fields on beam
axis. This approach paves the way to an analysis at the quantum level of the
spatial structure and angular momentum properties of singular light beams.Comment: 5 pages, 4 figure
Experimental status of the isoscalar S wave at low energy: pole and scattering length
The experimental results obtained in the last few years on kaon decays
(K and, above all, Ke4 decays) allow a reliable, model independent
determination of low energy scattering in the S0 wave. Using them and,
eventually, other sets of data, it is possible to give a precise
parametrization of the S0 wave as well as to find the scattering length and
effective range parameter. One can also perform an extrapolation to the pole of
the " resonance" []. We obtain the results
and, for the pole, M_\sigma=484\pm17 \mev,\quad\gammav_\sigma/2=
255\pm10 {\rm MeV}.Comment: Plain TeX;4 figures; improved data used; version to appear in Phys.
Rev.
Resonant control of spin dynamics in ultracold quantum gases by microwave dressing
We study experimentally interaction-driven spin oscillations in optical
lattices in the presence of an off-resonant microwave field. We show that the
energy shift induced by this microwave field can be used to control the spin
oscillations by tuning the system either into resonance to achieve near-unity
contrast or far away from resonance to suppress the oscillations. Finally, we
propose a scheme based on this technique to create a flat sample with either
singly- or doubly-occupied sites, starting from an inhomogeneous Mott
insulator, where singly- and doubly-occupied sites coexist.Comment: 4 pages, 5 figure
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