6,530 research outputs found
Adjoint operators, gauge invariant perturbations, and covariant symplectic structure for black holes in string theory
Expressions for the general and complete perturbations in terms of Debye
potentials of static charged black holes in string theory, valid for curvature
below the Planck scale, are derived starting from a decoupled set of equations
and using Wald's method of adjoint operators. Our results cover both extremal
and nonextremal black holes and are valid for arbitrary values of the dilaton
coupling parameter. The decoupled set is obtained using the Newman-Penrose
formulation of the Einstein-Maxwell-dilaton theory and involves naturally field
quantities invariant under both ordinary gauge transformations of the
electromagnetic potential perturbations and infinitesimal rotations of the
perturbed tetrad. Furthermore, using the recent pointed out relationship
between adjoint operators and conserved currents, a local continuity law for
the field perturbations in terms of the potentials is also obtained. It is
shown that such continuity equation implies the existence of conserved
quantities and of a covariant symplectic structure on the phase space. Future
extensions of the present results are discussed.Comment: LaTeX, 36 pages, submitted to J. Math. Phys. (2002
Perturbations in the Kerr-Newman Dilatonic Black Hole Background: I. Maxwell waves
In this paper we analyze the perturbations of the Kerr-Newman dilatonic black
hole background. For this purpose we perform a double expansion in both the
background electric charge and the wave parameters of the relevant quantities
in the Newman-Penrose formalism. We then display the gravitational, dilatonic
and electromagnetic equations, which reproduce the static solution (at zero
order in the wave parameter) and the corresponding wave equations in the Kerr
background (at first order in the wave parameter and zero order in the electric
charge). At higher orders in the electric charge one encounters corrections to
the propagations of waves induced by the presence of a non-vanishing dilaton.
An explicit computation is carried out for the electromagnetic waves up to the
asymptotic form of the Maxwell field perturbations produced by the interaction
with dilatonic waves. A simple physical model is proposed which could make
these perturbations relevant to the detection of radiation coming from the
region of space near a black hole.Comment: RevTeX, 36 pages in preprint style, 1 figure posted as a separate PS
file, submitted to Phys. Rev.
Microfield Dynamics of Black Holes
The microcanonical treatment of black holes as opposed to the canonical
formulation is reviewed and some major differences are displayed. In particular
the decay rates are compared in the two different pictures.Comment: 22 pages, 4 figures, Revtex, Minor change in forma
Can black holes and naked singularities be detected in accelerators?
We study the conditions for the existence of black holes that can be produced
in colliders at TeV-scale if the space-time is higher dimensional. On employing
the microcanonical picture, we find that their life-times strongly depend on
the details of the model. If the extra dimensions are compact (ADD model),
microcanonical deviations from thermality are in general significant near the
fundamental TeV mass and tiny black holes decay more slowly than predicted by
the canonical expression, but still fast enough to disappear almost
instantaneously. However, with one warped extra dimension (RS model),
microcanonical corrections are much larger and tiny black holes appear to be
(meta)stable. Further, if the total charge is not zero, we argue that naked
singularities do not occur provided the electromagnetic field is strictly
confined on an infinitely thin brane. However, they might be produced in
colliders if the effective thickness of the brane is of the order of the
fundamental length scale (~1/TeV).Comment: 6 pages, RevTeX 3, 1 figure and 1 table, important changes and
addition
Business Incubators: Creation of a Fit in Armenia
In this paper, we evaluate the extent to which business incubation services meet tenant’s needs. Additionally, we pose the question of whether the current business incubators actually cover the needs of a particular industry. Our empirical setting is a developing country in the Caucasian Region (Armenia) and we chose to research solely the IT industry. We employed a two stage procedure: first, we conducted interviews with pivotal people familiar with business incubation in Armenia; second, an electronic questionnaire survey was sent to the entire Armenian IT population. The results suggest a moderate need of IT companies for the typical business incubation services. Further, we show that incubated companies are generally satisfied with the services they enjoy albeit this satisfaction level decreases as the needs increase. Non-incubated companies, on the other hand, perceive incubation services to be valuable for their development and this value increases when their needs increase. Our study implies that a more extensive service provision is necessary to fully cover the needs of the Armenian IT industry for business incubation services
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