139,529 research outputs found
On two- and three-body descriptions of hybrid mesons
Hybrid mesons are exotic mesons in which the color field is not in its ground
state. Their understanding deserves interest from a theoretical point of view,
because it is intimately related to nonperturbative aspects of QCD. In this
work, we analyze and compare two different descriptions of hybrid mesons,
namely a two-body system with an excited string, or a three-body
system. In particular, we show that the constituent gluon approach
is equivalent to an effective excited string in the heavy hybrid sector.
Instead of a numerical resolution, we use the auxiliary field technique. It
allows to find simplified analytical mass spectra and wave functions, and still
leads to reliable qualitative predictions. We also investigate the light hybrid
sector, and found a mass for the lightest hybrid meson which is in satisfactory
agreement with lattice QCD and other effective models.Comment: 2 figure
Frequency and Phase Synchronization in Neuromagnetic Cortical Responses to Flickering-Color Stimuli
In our earlier study dealing with the analysis of neuromagnetic responses
(magnetoencephalograms - MEG) to flickering-color stimuli for a group of
control human subjects (9 volunteers) and a patient with photosensitive
epilepsy (a 12-year old girl), it was shown that Flicker-Noise Spectroscopy
(FNS) was able to identify specific differences in the responses of each
organism. The high specificity of individual MEG responses manifested itself in
the values of FNS parameters for both chaotic and resonant components of the
original signal. The present study applies the FNS cross-correlation function
to the analysis of correlations between the MEG responses simultaneously
measured at spatially separated points of the human cortex processing the
red-blue flickering color stimulus. It is shown that the cross-correlations for
control (healthy) subjects are characterized by frequency and phase
synchronization at different points of the cortex, with the dynamics of
neuromagnetic responses being determined by the low-frequency processes that
correspond to normal physiological rhythms. But for the patient, the frequency
and phase synchronization breaks down, which is associated with the suppression
of cortical regulatory functions when the flickering-color stimulus is applied,
and higher frequencies start playing the dominating role. This suggests that
the disruption of correlations in the MEG responses is the indicator of
pathological changes leading to photosensitive epilepsy, which can be used for
developing a method of diagnosing the disease based on the analysis with the
FNS cross-correlation function.Comment: 21 pages, 14 figures; submitted to "Laser Physics", 2010, 2
Phase transition for the frog model
We study a system of simple random walks on graphs, known as frog model. This
model can be described as follows: There are active and sleeping particles
living on some graph G. Each active particle performs a simple random walk with
discrete time and at each moment it may disappear with probability 1-p. When an
active particle hits a sleeping particle, the latter becomes active. Phase
transition results and asymptotic values for critical parameters are presented
for Z^d and regular trees
A short distance quark-antiquark potential
Leading terms of the static quark-antiquark potential in the background
perturbation theory are reviewed, including perturbative, nonperturbative and
interference ones. The potential is shown to describe lattice data at short
quark-antiquark separations with a good accuracy.Comment: 4 pages, 2 figures, talk at the NPD-2002 Conference, December 2-6,
ITEP, Moscow, references update
Microscopic derivation of the pion coupling to heavy-light mesons
The Goldberger--Treiman relation for heavy--light systems is derived in the
context of a quark model. As a paradigmatic example, the case of is studied in detail. The fundamental role played by the pion
two-component wave function, in the context of the Salpeter equation, is
emphasized.Comment: 6 pages, 2 figures, version to appear in Phys. Rev.
Lax pairs, Painlev\'e properties and exact solutions of the alogero Korteweg-de Vries equation and a new (2+1)-dimensional equation
We prove the existence of a Lax pair for the Calogero Korteweg-de Vries
(CKdV) equation. Moreover, we modify the T operator in the the Lax pair of the
CKdV equation, in the search of a (2+1)-dimensional case and thereby propose a
new equation in (2+1) dimensions. We named this the (2+1)-dimensional CKdV
equation. We show that the CKdV equation as well as the (2+1)-dimensional CKdV
equation are integrable in the sense that they possess the Painlev\'e property.
Some exact solutions are also constructed
Determination of the Fragmentation Parameters of the Multi-charge Component of Primary Cosmic Rays
Determination of fragmentation parameters of multicharge component of primary cosmic ray
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