2,344 research outputs found
Evolution equation of quantum tomograms for a driven oscillator in the case of the general linear quantization
The symlectic quantum tomography for the general linear quantization is
introduced. Using the approach based upon the Wigner function techniques the
evolution equation of quantum tomograms is derived for a parametric driven
oscillator.Comment: 11 page
Extremal black holes in D=4 Gauss-Bonnet gravity
We show that four-dimensional Einstein-Maxwell-Dilaton-Gauss-Bonnet gravity
admits asymptotically flat black hole solutions with a degenerate event horizon
of the Reissner-Nordstr\"om type . Such black holes exist for
the dilaton coupling constant within the interval .
Black holes must be endowed with an electric charge and (possibly) with
magnetic charge (dyons) but they can not be purely magnetic. Purely electric
solutions are constructed numerically and the critical dilaton coupling is
determined . For each value of the dilaton
coupling within this interval and for a fixed value of the Gauss--Bonnet
coupling we have a family of black holes parameterized by their
electric charge. Relation between the mass, the electric charge and the dilaton
charge at both ends of the allowed interval of is reminiscent of the BPS
condition for dilaton black holes in the Einstein-Maxwell-Dilaton theory. The
entropy of the DGB extremal black holes is twice the Bekenstein-Hawking
entropy.Comment: New material and references added, errors corrected including higher
decimals in a_cr, figures improve
Global solutions for higher-dimensional stretched small black holes
Small black holes in heterotic string theory have vanishing horizon area at
the supergravity level, but the horizon is stretched to the finite radius
geometry once higher curvature corrections are turned
on. This has been demonstrated to give good agreement with microscopic entropy
counting. Previous considerations, however, were based on the classical local
solutions valid only in the vicinity of the event horizon. Here we address the
question of global existence of extremal black holes in the -dimensional
Einstein-Maxwell-Dilaton theory with the Gauss-Bonnet term introducing a
variable dilaton coupling as a parameter. We show that asymptotically flat
black holes exist only in a bounded region of the dilaton couplings where depends on . For (but not for ) the allowed range of includes the heterotic string values. For numerical solutions meet weak naked singularities at finite radii
(spherical cusps), where the scalar curvature diverges as
. For cusps are met in pairs, so that
solutions can be formally extended to asymptotically flat infinity choosing a
suitable integration variable. We show, however, that radial geodesics cannot
be continued through the cusp singularities, so such a continuation is
unphysical.Comment: 26 pages, 19 figures, minor correction
Change in stability of solid solution at radiation influence
Stability of solid solution at radiation influence has been investigated. Expressions for diffusion streams of binary alloy components, which specify the existence of temperature interval in which the phenomenon of ascending diffusion of elements is observed, were received. Vacancy characters of diffusion, configuration entropy, and potential energy of atomic bonds were considered at derivation. The ascending diffusion testifies to stability infringement of homogeneous solid solution - stratification. Influence of radiation is connected with increase in concentration of vacancies which changes the energy of atomic bonds and, simultaneously, accelerates diffusion processes. The condition of alloy stability with regard to stratification at radiating influence was obtaine
Bound, virtual and resonance -matrix poles from the Schr\"odinger equation
A general method, which we call the potential -matrix pole method, is
developed for obtaining the -matrix pole parameters for bound, virtual and
resonant states based on numerical solutions of the Schr\"odinger equation.
This method is well-known for bound states. In this work we generalize it for
resonant and virtual states, although the corresponding solutions increase
exponentially when . Concrete calculations are performed for the
ground and the first excited states of , the resonance
states (, ), low-lying states of and
, and the subthreshold resonances in the proton-proton system. We
also demonstrate that in the case the broad resonances their energy and width
can be found from the fitting of the experimental phase shifts using the
analytical expression for the elastic scattering -matrix. We compare the
-matrix pole and the -matrix for broad resonance in
Comment: 14 pages, 5 figures (figures 3 and 4 consist of two figures each) and
4 table
Extremal dyonic black holes in D=4 Gauss-Bonnet gravity
We investigate extremal dyon black holes in the Einstein-Maxwell-dilaton
(EMD) theory with higher curvature corrections in the form of the Gauss-Bonnet
density coupled to the dilaton. In the same theory without the Gauss-Bonnet
term the extremal dyon solutions exist only for discrete values of the dilaton
coupling constant . We show that the Gauss-Bonnet term acts as a dyon hair
tonic enlarging the allowed values of to continuous domains in the plane
the second parameter being the magnetic charge. In the limit of the
vanishing curvature coupling (a large magnetic charge) the dyon solutions
obtained tend to the Reissner-Nordstr\"om solution but not to the extremal
dyons of the EMD theory. Both solutions have the same values of the horizon
radius as a function of charges. The entropy of new dyonic black holes
interpolates between the Bekenstein-Hawking value in the limit of the large
magnetic charge (equivalent to the vanishing Gauss-Bonnet coupling) and twice
this value for the vanishing magnetic charge. Although an expression for the
entropy can be obtained analytically using purely local near-horizon solutions,
its interpretation as the black hole entropy is legitimate only once the global
black hole solution is known to exist, and we obtain numerically the
corresponding conditions on the parameters. Thus, a purely local analysis is
insufficient to fully understand the entropy of the curvature corrected black
holes. We also find dyon solutions which are not asymptotically flat, but
approach the linear dilaton background at infinity. They describe magnetic
black holes on the electric linear dilaton background.Comment: 19 pages, 3 figures, revtex
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