277 research outputs found
Spinning particles in Taub-NUT space
The geodesic motion of pseudo-classical spinning particles in Euclidean
Taub-NUT space is analysed. The constants of motion are expressed in terms of
Killing-Yano tensors. Some previous results from the literature are corrected.Comment: LaTeX, 8 page
All the Four Dimensional Static, Spherically Symmetric Solutions of Abelian Kaluza-Klein Theory
We present the explicit form for all the four dimensional, static,
spherically symmetric solutions in -d Abelian Kaluza-Klein theory by
performing a subset of transformations corresponding to four
boosts on the Schwarzschild solution, supplemented by
transformations. The solutions are parameterized by the mass , Taub-Nut
charge , electric and magnetic
charges. Non-extreme black holes (with zero Taub-NUT charge) have either the
Reissner-Nordstr\" om or Schwarzschild global space-time. Supersymmetric
extreme black holes have a null or naked singularity, while non-supersymmetric
extreme ones have a global space-time of extreme Reissner-Nordstr\" om black
holes.Comment: 8 pages, uses RevTex, improved version to appear in Phys. Rev. Let
STATIC FOUR-DIMENSIONAL ABELIAN BLACK HOLES IN KALUZA-KLEIN THEORY
Static, four-dimensional (4-d) black holes (BH's) in ()-d Kaluza-Klein
(KK) theory with Abelian isometry and diagonal internal metric have at most one
electric () and one magnetic () charges, which can either come from the
same -gauge field (corresponding to BH's in effective 5-d KK theory) or
from different ones (corresponding to BH's with isometry
of an effective 6-d KK theory). In the latter case, explicit non-extreme
solutions have the global space-time of Schwarzschild BH's, finite temperature,
and non-zero entropy. In the extreme (supersymmetric) limit the singularity
becomes null, the temperature saturates the upper bound
, and entropy is zero. A class of KK BH's with
constrained charge configurations, exhibiting a continuous electric-magnetic
duality, are generated by global transformations on the above classes
of the solutions.Comment: 11 pages, 2 Postscript figures. uses RevTeX and psfig.sty (for figs)
paper and figs also at ftp://dept.physics.upenn.edu/pub/Cvetic/UPR-645-
Virtual Black Holes
One would expect spacetime to have a foam-like structure on the Planck scale
with a very high topology. If spacetime is simply connected (which is assumed
in this paper), the non-trivial homology occurs in dimension two, and spacetime
can be regarded as being essentially the topological sum of and
bubbles. Comparison with the instantons for pair creation of black holes
shows that the bubbles can be interpreted as closed loops of
virtual black holes. It is shown that scattering in such topological
fluctuations leads to loss of quantum coherence, or in other words, to a
superscattering matrix that does not factorise into an matrix and its
adjoint. This loss of quantum coherence is very small at low energies for
everything except scalar fields, leading to the prediction that we may never
observe the Higgs particle. Another possible observational consequence may be
that the angle of QCD is zero without having to invoke the
problematical existence of a light axion. The picture of virtual black holes
given here also suggests that macroscopic black holes will evaporate down to
the Planck size and then disappear in the sea of virtual black holes.Comment: 24p, LaTeX, 3 postscript figures included with epsf sent in a
seperate uuencoded fil
Decay Modes of Intersecting Fluxbranes
Just as the single fluxbrane is quantum mechanically unstable to the
nucleation of a locally charged spherical brane, so intersecting fluxbranes are
unstable to various decay modes. Each individual element of the intersection
can decay via the nucleation of a spherical brane, but uncharged spheres can
also be nucleated in the region of intersection. For special values of the
fluxes, however, intersecting fluxbranes are supersymmetric, and so are
expected to be stable. We explicitly consider the instanton describing the
decay modes of the two--element intersection (an F5-brane in the string theory
context), and show that in dimensions greater than four the action for the
decay mode of the supersymmetric intersection diverges. This observation allows
us to show that stable intersecting fluxbranes should also exist in type 0A
string theory.Comment: 19 pages, 6 figures. References adde
Fluctuations of an evaporating black hole from back reaction of its Hawking radiation: Questioning a premise in earlier work
This paper delineates the first steps in a systematic quantitative study of
the spacetime fluctuations induced by quantum fields in an evaporating black
hole. We explain how the stochastic gravity formalism can be a useful tool for
that purpose within a low-energy effective field theory approach to quantum
gravity. As an explicit example we apply it to the study of the
spherically-symmetric sector of metric perturbations around an evaporating
black hole background geometry. For macroscopic black holes we find that those
fluctuations grow and eventually become important when considering sufficiently
long periods of time (of the order of the evaporation time), but well before
the Planckian regime is reached. In addition, the assumption of a simple
correlation between the fluctuations of the energy flux crossing the horizon
and far from it, which was made in earlier work on spherically-symmetric
induced fluctuations, is carefully analyzed and found to be invalid. Our
analysis suggests the existence of an infinite amplitude for the fluctuations
of the horizon as a three-dimensional hypersurface. We emphasize the need for
understanding and designing operational ways of probing quantum metric
fluctuations near the horizon and extracting physically meaningful information.Comment: 10 pages, REVTeX; minor changes, a few references added and a brief
discussion of their relevance included. To appear in the proceedings of the
10th Peyresq meeting. Dedicated to Rafael Sorkin on the occasion of his 60th
birthda
Paradox as invitation to act in problematic change situations
It has been argued that organizational life typically contains paradoxical situations such as efforts to manage change which nonetheless seem to reinforce inertia. Four logical options for coping with paradox have been explicated, three of which seek resolution and one of which âkeeps the paradox openâ. The purpose of this article is to explore the potential for managerial action where the paradox is held open through the use of theory on âserious playfulnessâ. Our argument is that paradoxes, as intrinsic features in organizational life, cannot always be resolved through cognitive processes. What may be possible, however, is that such paradoxes are transformed, or âmoved onâ through action and as a result the overall change effort need not be stalled by the existence of embedded paradoxes
Duality Transformations in Supersymmetric Yang-Mills Theories coupled to Supergravity,
We consider duality transformations in N=2, d=4 Yang--Mills theory coupled to
N=2 supergravity. A symplectic and coordinate covariant framework is
established, which allows one to discuss stringy `classical and quantum duality
symmetries' (monodromies), incorporating T and S dualities. In particular, we
shall be able to study theories (like N=2 heterotic strings) which are
formulated in symplectic basis where a `holomorphic prepotential' F does not
exist, and yet give general expressions for all relevant physical quantities.
Duality transformations and symmetries for the N=1 matter coupled Yang--Mills
supergravity system are also exhibited. The implications of duality symmetry on
all N>2 extended supergravities are briefly mentioned. We finally give the
general form of the central charge and the N=2 semiclassical spectrum of the
dyonic BPS saturated states (as it comes by truncation of the N=4 spectrum).Comment: 41 pages, harvmac, no figures. References added, and minor printing
error corrected
Force and Motion Generation of Molecular Motors: A Generic Description
We review the properties of biological motor proteins which move along linear
filaments that are polar and periodic. The physics of the operation of such
motors can be described by simple stochastic models which are coupled to a
chemical reaction. We analyze the essential features of force and motion
generation and discuss the general properties of single motors in the framework
of two-state models. Systems which contain large numbers of motors such as
muscles and flagella motivate the study of many interacting motors within the
framework of simple models. In this case, collective effects can lead to new
types of behaviors such as dynamic instabilities of the steady states and
oscillatory motion.Comment: 29 pages, 9 figure
Mathematics of Gravitational Lensing: Multiple Imaging and Magnification
The mathematical theory of gravitational lensing has revealed many generic
and global properties. Beginning with multiple imaging, we review
Morse-theoretic image counting formulas and lower bound results, and
complex-algebraic upper bounds in the case of single and multiple lens planes.
We discuss recent advances in the mathematics of stochastic lensing, discussing
a general formula for the global expected number of minimum lensed images as
well as asymptotic formulas for the probability densities of the microlensing
random time delay functions, random lensing maps, and random shear, and an
asymptotic expression for the global expected number of micro-minima. Multiple
imaging in optical geometry and a spacetime setting are treated. We review
global magnification relation results for model-dependent scenarios and cover
recent developments on universal local magnification relations for higher order
caustics.Comment: 25 pages, 4 figures. Invited review submitted for special issue of
General Relativity and Gravitatio
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