2,022 research outputs found
QCD-Thermodynamics using 5-dim Gravity
We calculate the critical temperature and free energy of the gluon plasma
using the dilaton potential arXiv:0911.0627[hep-ph] in the gravity theory of
AdS/QCD. The finite temperature observables are calculated in two ways: first,
from the Page-Hawking computation of the free energy, and secondly using the
Bekenstein-Hawking proportionality of the entropy with the area of the horizon.
Renormalization is well defined, because the T=0 theory has asymptotic freedom.
We further investigate the change of the critical temperature with the number
of flavours induced by the change of the running coupling constant in the
quenched theory. The finite temperature behaviour of the speed of sound,
spatial string tension and vacuum expectation value of the Polyakov loop follow
from the corresponding string theory in AdS_5.Comment: 38 pages, 12 figure
Cavity solitons in vertical-cavity surface-emitting lasers
We investigate a control of the motion of localized structures of light by
means of delay feedback in the transverse section of a broad area nonlinear
optical system. The delayed feedback is found to induce a spontaneous motion of
a solitary localized structure that is stationary and stable in the absence of
feedback. We focus our analysis on an experimentally relevant system namely the
Vertical-Cavity Surface-Emitting Laser (VCSEL). In the absence of the delay
feedback we present experimental evidence of stationary localized structures in
a 80 m aperture VCSEL. The spontaneous formation of localized structures
takes place above the lasing threshold and under optical injection. Then, we
consider the effect of the time-delayed optical feedback and investigate
analytically the role of the phase of the feedback and the carrier lifetime on
the self-mobility properties of the localized structures. We show that these
two parameters affect strongly the space time dynamics of two-dimensional
localized structures. We derive an analytical formula for the threshold
associated with drift instability of localized structures and a normal form
equation describing the slow time evolution of the speed of the moving
structure.Comment: 7 pages, 5 figure
Direct observation of mode-coupling instability in two-dimensional plasma crystals
Dedicated experiments on melting of 2D plasma crystals were carried out. The
melting was always accompanied by spontaneous growth of the particle kinetic
energy, suggesting a universal plasma-driven mechanism underlying the process.
By measuring three principal dust-lattice (DL) wave modes simultaneously, it is
unambiguously demonstrated that the melting occurs due to the resonance
coupling between two of the DL modes. The variation of the wave modes with the
experimental conditions, including the emergence of the resonant (hybrid)
branch, reveals exceptionally good agreement with the theory of mode-coupling
instability.Comment: 4 pages, submitted to Physical Review Letter
Delayed feedback control of self-mobile cavity solitons in a wide-aperture laser with a saturable absorber
We investigate the spatiotemporal dynamics of cavity solitons in a broad area
vertical-cavity surface-emitting laser with saturable absorption subjected to
time-delayed optical feedback. Using a combination of analytical, numerical and
path continuation methods we analyze the bifurcation structure of stationary
and moving cavity solitons and identify two different types of traveling
localized solutions, corresponding to slow and fast motion. We show that the
delay impacts both stationary and moving solutions either causing drifting and
wiggling dynamics of initially stationary cavity solitons or leading to
stabilization of intrinsically moving solutions. Finally, we demonstrate that
the fast cavity solitons can be associated with a lateral mode-locking regime
in a broad-area laser with a single longitudinal mode
Boundary Shape and Casimir Energy
Casimir energy changes are investigated for geometries obtained by small but
arbitrary deformations of a given geometry for which the vacuum energy is
already known for the massless scalar field. As a specific case, deformation of
a spherical shell is studied. From the deformation of the sphere we show that
the Casimir energy is a decreasing function of the surface to volume ratio. The
decreasing rate is higher for less smooth deformations.Comment: 12 page
Radiometric force in dusty plasmas
A radiofrequency glow discharge plasma, which is polluted with a certain
number of dusty grains, is studied. In addition to various dusty plasma
phenomena, several specific colloidal effects should be considered. We focus on
radiometric forces, which are caused by inhomogeneous temperature distribution.
Aside from thermophoresis, the role of temperature distribution in dusty
plasmas is an open question. It is shown that inhomogeneous heating of the
grain by ion flows results in a new photophoresis like force, which is specific
for dusty discharges. This radiometric force can be observable under conditions
of recent microgravity experiments.Comment: 4 pages, amsmat
Twist Deformation of the rank one Lie Superalgebra
The Drinfeld twist is applyed to deforme the rank one orthosymplectic Lie
superalgebra . The twist element is the same as for the Lie
algebra due to the embedding of the into the superalgebra .
The R-matrix has the direct sum structure in the irreducible representations of
. The dual quantum group is defined using the FRT-formalism. It
includes the Jordanian quantum group as subalgebra and Grassmann
generators as well.Comment: LaTeX, 9 page
Five-Loop Vacuum Energy Beta Function in phi^4 Theory with O(N)-Symmetric and Cubic Interactions
The beta function of the vacuum energy density is analytically computed at
the five-loop level in O(N)-symmetric phi^4 theory, using dimensional
regularization in conjunction with the MSbar scheme. The result for the case of
a cubic anisotropy is also given. It is pointed out how to also obtain the beta
function of the coupling and the gamma function of the mass from vacuum graphs.
This method may be easier than traditional approaches.Comment: 16 pages, LaTeX; "note added" fixe
Environments for Magnetic Field Amplification by Cosmic Rays
We consider a recently discovered class of instabilities, driven by cosmic
ray streaming, in a variety of environments. We show that although these
instabilities have been discussed primarily in the context of supernova driven
interstellar shocks, they can also operate in the intergalactic medium and in
galaxies with weak magnetic fields, where, as a strong source of helical
magnetic fluctuations, they could contribute to the overall evolution of the
magnetic field. Within the Milky Way, these instabilities are strongest in warm
ionized gas, and appear to be weak in hot, low density gas unless the injection
efficiency of cosmic rays is very high.Comment: 9 pages, 8 figures; Accepted to Ap
- …