13,069 research outputs found
Lorenz-Mie scattering of focused light via complex focus fields: an analytic treatment
The Lorenz-Mie scattering of a wide class of focused electromagnetic fields
off spherical particles is studied. The focused fields in question are
constructed through complex focal displacements, leading to closed-form
expressions that can exhibit several interesting physical properties, such as
orbital and/or spin angular momentum, spatially-varying polarization, and a
controllable degree of focusing. These fields constitute complete bases that
can be considered as nonparaxial extensions of the standard Laguerre-Gauss
beams and the recently proposed polynomials-of-Gaussians beams. Their analytic
form turns out to lead also to closed-form expressions for their multipolar
expansion. Such expansion can be used to compute the field scattered by a
spherical particle and the resulting forces and torques exerted on it, for any
relative position between the field's focus and the particle.Comment: 11 pages, 7 figure
Pairs-Production of Higgs in Association with Bottom Quarks Pairs at Colliders
In a previous paper, we studied the Higgs pair production in the standard
model with the reaction . Based on this, we study
the Higgs pair production via . We evaluate the
total cross section of and calculate the number total of events
considering the complete set of Feynman diagrams at tree-level, and compare
this process with the process . The numerical
computation is done for the energy which is expected to be available at a
possible Next Linear Collider with a center-of-mass energy and luminosity 1000 .Comment: 12 pages, 6 figure
Functional centrality in graphs
In this paper we introduce the functional centrality as a generalization of
the subgraph centrality. We propose a general method for characterizing nodes
in the graph according to the number of closed walks starting and ending at the
node. Closed walks are appropriately weighted according to the topological
features that we need to measure
On the connected component of compact composition operators on the Hardy space
We show that there exist non-compact composition operators in the connected
component of the compact ones on the classical Hardy space on the unit
disc. This answers a question posed by Shapiro and Sundberg in 1990. We also
establish an improved version of a theorem of MacCluer, giving a lower bound
for the essential norm of a difference of composition operators in terms of the
angular derivatives of their symbols. As a main tool we use Aleksandrov-Clark
measures.Comment: 16 page
Anderson Localization in Disordered Vibrating Rods
We study, both experimentally and numerically, the Anderson localization
phenomenon in torsional waves of a disordered elastic rod, which consists of a
cylinder with randomly spaced notches. We find that the normal-mode wave
amplitudes are exponentially localized as occurs in disordered solids. The
localization length is measured using these wave amplitudes and it is shown to
decrease as a function of frequency. The normal-mode spectrum is also measured
as well as computed, so its level statistics can be analyzed. Fitting the
nearest-neighbor spacing distribution a level repulsion parameter is defined
that also varies with frequency. The localization length can then be expressed
as a function of the repulsion parameter. There exists a range in which the
localization length is a linear function of the repulsion parameter, which is
consistent with Random Matrix Theory. However, at low values of the repulsion
parameter the linear dependence does not hold.Comment: 10 pages, 6 figure
Exact relativistic models of thin disks around static black holes in a magnetic field
The exact superposition of a central static black hole with surrounding thin
disk in presence of a magnetic field is investigated. We consider two models of
disk, one of infinite extension based on a Kuzmin-Chazy-Curzon metric and other
finite based on the first Morgan-Morgan disk. We also analyze a simple model of
active galactic nuclei consisting of black hole, a Kuzmin-Chazy-Curzon disk and
two rods representing jets, in presence of magnetic field. To explain the
stability of the disks we consider the matter of the disk made of two
pressureless streams of counterrotating charged particles (counterrotating
model) moving along electrogeodesic. Using the Rayleigh criterion we derivate
for circular orbits the stability conditions of the particles of the streams.
The influence of the magnetic field on the matter properties of the disk and on
its stability are also analyzed.Comment: 17 pages, 14 figures. arXiv admin note: text overlap with
arXiv:gr-qc/0409109 by other author
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