6,124 research outputs found
Complete Semiclassical Treatment of the Quantum Black Hole Problem
Two types of semiclassical calculations have been used to study quantum
effects in black hole backgrounds, the WKB and the mean field approaches. In
this work we systematically reconstruct the logical implications of both
methods on quantum black hole physics and provide the link between these two
approaches. Our conclusions completely support our previous findings based
solely on the WKB method: quantum black holes are effectively p-brane
excitations and, consequently, no information loss paradox exists in this
problem.Comment: 14 pages, REVTE
Conjectures on Non-Local Effects in String Black Holes
We consider modifications to general relativity by the non-local (classical
and quantum) string effects for the case of a D-dimensional Scwarzschild black
hole. The classical non-local effects do not alter the spacetime topology (the
horizon remains unshifted, at least perturbatively). We suggest a simple
analytic continuation of the perturbative result into the non-perturbative
domain, which eliminates the black hole singularity at the origin and yields an
ultraviolet-finite theory of quantum gravity. We investigate the quantum non-
local effects (including massive modes) and argue that the inclusion of these
back reactions resolves the problem of the thermal spectrum in the semi-
classical approach of field quantization in a black hole background, through
the bootstrap condition. The density of states for both the quantum and thermal
interpretation of the WKB formula are finally shown to differ quant- itatively
when including the non-local effects.Comment: 16 pages, REVTE
Black Extended Objects, Naked Singularities and P-Branes
We treat the horizons of charged, dilaton black extended objects as quantum
mechanical objects. We show that the S matrix for such an object can be written
in terms of a p-brane-like action. The requirements of unitarity of the S
matrix and positivity of the p-brane tension equivalent severely restrict the
number of space-time dimensions and the allowed values of the dilaton parameter
a. Generally, black objects transform at the extremal limit into p-branes.Comment: 9 pages, REVTE
Bosonic D-branes at finite temperature with an external field
Bosonic boundary states at finite temperature are constructed as solutions of
boundary conditions at for bosonic open strings with a constant gauge
field coupled to the boundary. The construction is done in the
framework of thermo field dynamics where a thermal Bogoliubov transformation
maps states and operators to finite temperature. Boundary states are given in
terms of states from the direct product space between the Fock space of the
closed string and another identical copy of it. By analogy with zero
temperature, the boundary states heve the interpretation of -brane at
finite temperature. The boundary conditions admit two different solutions. The
entropy of the closed string in a -brane state is computed and analysed. It
is interpreted as the entropy of the -brane at finite temperature.Comment: 21 pages, Latex, revised version with minor corrections and
references added, to be published in Phys. Rev.
Dilatonic Black Holes, Naked Singularities and Strings
We extend a previous calculation which treated Schwarschild black hole
horizons as quantum mechanical objects to the case of a charged, dilaton black
hole. We show that for a unique value of the dilaton parameter `a', which is
determined by the condition of unitarity of the S matrix, black holes transform
at the extremal limit into strings.Comment: 8 pages, REVTE
Effect of magnetic field on the phase transition in a dusty plasma
The formation of self-consistent crystalline structure is a well-known
phenomenon in complex plasmas. In most experiments the pressure and rf power
are the main controlling parameters in determining the phase of the system. We
have studied the effect of externally applied magnetic field on the
configuration of plasma crystals, suspended in the sheath of a radio-frequency
discharge using the Magnetized Dusty Plasma Experiment (MDPX) device.
Experiments are performed at a fixed pressure and rf power where a crystalline
structure is formed within a confining ring. The magnetic field is then
increased from 0 to 1.28 T. We report on the breakdown of the crystalline
structure with increasing magnetic field. The magnetic field affects the
dynamics of the plasma particles and first leads to a rotation of the crystal.
At higher magnetic field, there is a radial variation (shear) in the angular
velocity of the moving particles which we believe leads to the melting of the
crystal. This melting is confirmed by evaluating the variation of the pair
correlation function as a function of magnetic field.Comment: 9 pages, 5 figure
- …