1,315 research outputs found
Quantum Geometry and Thermal Radiation from Black Holes
A quantum mechanical description of black hole states proposed recently
within non-perturbative quantum gravity is used to study the emission and
absorption spectra of quantum black holes. We assume that the probability
distribution of states of the quantum black hole is given by the ``area''
canonical ensemble, in which the horizon area is used instead of energy, and
use Fermi's golden rule to find the line intensities. For a non-rotating black
hole, we study the absorption and emission of s-waves considering a special set
of emission lines. To find the line intensities we use an analogy between a
microscopic state of the black hole and a state of the gas of atoms.Comment: 19 pages, 4 figures, modified version to appear in Class. Quant. Gra
On the Nature of Black Holes in Loop Quantum Gravity
A genuine notion of black holes can only be obtained in the fundamental
framework of quantum gravity resolving the curvature singularities and giving
an account of the statistical mechanical, microscopic degrees of freedom able
to explain the black hole thermodynamical properties. As for all quantum
systems, a quantum realization of black holes requires an operator algebra of
the fundamental observables of the theory which is introduced in this study
based on aspects of loop quantum gravity. From the eigenvalue spectra of the
quantum operators for the black hole area, charge and angular momentum, it is
demonstrated that a strict bound on the extensive parameters, different from
the relation arising in classical general relativity, holds, implying that the
extremal black hole state can neither be measured nor can its existence be
proven. This is, as turns out, a result of the specific form of the chosen
angular momentum operator and the corresponding eigenvalue spectrum, or rather
the quantum measurement process of angular momentum. Quantum mechanical
considerations and the lowest, non-zero eigenvalue of the loop quantum gravity
black hole mass spectrum indicate, on the one hand, a physical Planck scale
cutoff of the Hawking temperature law and, on the other hand, give upper and
lower bounds on the numerical value of the Immirzi parameter. This analysis
provides an approximative description of the behavior and the nature of quantum
black holes
Counting surface states in the loop quantum gravity
We adopt the point of view that (Riemannian) classical and (loop-based)
quantum descriptions of geometry are macro- and micro-descriptions in the usual
statistical mechanical sense. This gives rise to the notion of geometrical
entropy, which is defined as the logarithm of the number of different quantum
states which correspond to one and the same classical geometry configuration
(macro-state). We apply this idea to gravitational degrees of freedom induced
on an arbitrarily chosen in space 2-dimensional surface. Considering an
`ensemble' of particularly simple quantum states, we show that the geometrical
entropy corresponding to a macro-state specified by a total area of
the surface is proportional to the area , with being
approximately equal to . The result holds both for case of open
and closed surfaces. We discuss briefly physical motivations for our choice of
the ensemble of quantum states.Comment: This paper is a substantially modified version of the paper `The
Bekenstein bound and non-perturbative quantum gravity'. Although the main
result (i.e. the result of calculation of the number of quantum states that
correspond to one and the same area of 2-d surface) remains unchanged, it is
presented now from a different point of view. The new version contains a
discussion both of the case of open and closed surfaces, and a discussion of
a possibility to generalize the result obtained considering arbitrary surface
quantum states. LaTeX, 21 pages, 6 figures adde
In-plane fluxon in layered superconductors with arbitrary number of layers
I derive an approximate analytic solution for the in-plane vortex (fluxon) in
layered superconductors and stacked Josephson junctions (SJJ's) with arbitrary
number of layers. The validity of the solution is verified by numerical
simulation. It is shown that in SJJ's with large number of thin layers,
phase/current and magnetic field of the fluxon are decoupled from each other.
The variation of phase/current is confined within the Josephson penetration
depth, , along the layers, while magnetic field decays at the
effective London penetration depth, . For comparison
with real high- superconducting samples, large scale numerical simulations
with up to 600 SJJ's and with in-plane length up to 4000 %, are
presented. It is shown, that the most striking feature of the fluxon is a
Josephson core, manifesting itself as a sharp peak in magnetic induction at the
fluxon center.Comment: 4 pages, 4 figures. Was presented in part at the First Euroconference
on Vortex Matter in Superconductors (Crete, September 1999
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