175 research outputs found
Exact Primordial Black Strings in Four Dimensions
A solution of effective string theory in four dimensions is presented which
admits interpretation of a rotating black cosmic string. It is constructed by
tensoring the three dimensional black hole, extended with the Kalb-Ramond
axion, with a flat direction. The physical interpretation of the solution is
discussed, with special attention on the axion, which is found to play a role
very similar to a Higgs field. Finally, it is pointed out that the solution
represents an exact WZWN model on the string world sheet, to all
orders in the inverse string tension .Comment: 11 pages plain TeX, Univ. of Alberta preprint Alberta-THY-14-199
Black Rings, Supertubes, and a Stringy Resolution of Black Hole Non-Uniqueness
In order to address the issues raised by the recent discovery of
non-uniqueness of black holes in five dimensions, we construct a solution of
string theory at low energies describing a five-dimensional spinning black ring
with three charges that can be interpreted as D1-brane, D5-brane, and momentum
charges. The solution possesses closed timelike curves (CTCs) and other
pathologies, whose origin we clarify. These pathologies can be avoided by
setting any one of the charges, e.g. the momentum, to zero. We argue that the
D1-D5-charged black ring, lifted to six dimensions, describes the thermal
excitation of a supersymmetric D1-D5 supertube, which is in the same U-duality
class as the D0-F1 supertube. We explain how the stringy microscopic
description of the D1-D5 system distinguishes between a spherical black hole
and a black ring with the same asymptotic charges, and therefore provides a
(partial) resolution of the non-uniqueness of black holes in five dimensions.Comment: 33 pages, 1 figur
Observations of quasi-periodic solar X-ray emission as a result of MHD oscillations in a system of multiple flare loops
We investigate the solar flare of 20 October 2002. The flare was accompanied
by quasi-periodic pulsations (QPP) of both thermal and nonthermal hard X-ray
emissions (HXR) observed by RHESSI in the 3-50 keV energy range. Analysis of
the HXR time profiles in different energy channels made with the Lomb
periodogram indicates two statistically significant time periods of about 16
and 36 seconds. The 36-second QPP were observed only in the nonthermal HXR
emission in the impulsive phase of the flare. The 16-second QPP were more
pronounced in the thermal HXR emission and were observed both in the impulsive
and in the decay phases of the flare. Imaging analysis of the flare region, the
determined time periods of the QPP and the estimated physical parameters of
magnetic loops in the flare region allow us to interpret the observations as
follows. 1) In the impulsive phase energy was released and electrons were
accelerated by successive acts with the average time period of about 36 seconds
in different parts of two spatially separated, but interacting loop systems of
the flare region. 2) The 36-second periodicity of energy release could be
caused by the action of fast MHD oscillations in the loops connecting these
flaring sites. 3) During the first explosive acts of energy release the MHD
oscillations (most probably the sausage mode) with time period of 16 seconds
were excited in one system of the flare loops. 4) These oscillations were
maintained by the subsequent explosive acts of energy release in the impulsive
phase and were completely damped in the decay phase of the flare.Comment: 14 pages, 4 figure
Waardevolle perspectieven voor vlees
Dit rapport doet verslag van een onderzoek waarin is gekeken hoe vlees in de keten op een andere manier tot waarde kan worden gebracht zodat dit lonend is voor de partijen in de keten. Hierbij geldt: de beloning komt zo veel mogelijk toe aan degene die de toegevoegde waarde levert. Dit initiatief richt zich daarbij op het ontwikkelen en beoordelen van alternatieve businessmodellen met een ander 'waarde(n)perspectief' voor pluimvee- en varkensvlees(producten)
Topology, Entropy and Witten Index of Dilaton Black Holes
We have found that for extreme dilaton black holes an inner boundary must be
introduced in addition to the outer boundary to give an integer value to the
Euler number. The resulting manifolds have (if one identifies imaginary time)
topology and Euler number in contrast to
the non-extreme case with . The entropy of extreme dilaton black
holes is already known to be zero. We include a review of some recent ideas due
to Hawking on the Reissner-Nordstr\"om case. By regarding all extreme black
holes as having an inner boundary, we conclude that the entropy of {\sl all}
extreme black holes, including black holes, vanishes. We discuss the
relevance of this to the vanishing of quantum corrections and the idea that the
functional integral for extreme holes gives a Witten Index. We have studied
also the topology of ``moduli space'' of multi black holes. The quantum
mechanics on black hole moduli spaces is expected to be supersymmetric despite
the fact that they are not HyperK\"ahler since the corresponding geometry has
torsion unlike the BPS monopole case. Finally, we describe the possibility of
extreme black hole fission for states with an energy gap. The energy released,
as a proportion of the initial rest mass, during the decay of an
electro-magnetic black hole is 300 times greater than that released by the
fission of an nucleus.Comment: 51 pages, 4 figures, LaTeX. Considerably extended version. New
sections include discussion of the Witten index, topology of the moduli
space, black hole sigma model, and black hole fission with huge energy
releas
Supersymmetry and Integrability in Planar Mechanical Systems
We present an N=2-supersymmetric mechanical system whose bosonic sector, with
two degrees of freedom, stems from the reduction of an SU(2) Yang-Mills theory
with the assumption of spatially homogeneous field configurations and a
particular ansatz imposed on the gauge potentials in the dimensional reduction
procedure. The Painleve test is adopted to discuss integrability and we focus
on the role of supersymmetry and parity invariance in two space dimensions for
the attainment of integrable or chaotic models. Our conclusion is that the
relationships among the parameters imposed by supersymmetry seem to drastically
reduce the number of possibilities for integrable interaction potentials of the
mechanical system under consideration.Comment: 20 pages, 3 figure
Active Galaxies in the UV
In this article we present different aspects of AGN studies demonstrating the
importance of the UV spectral range. Most important diagnostic lines for
studying the general physical conditions as well as the metalicities in the
central broad line region in AGN are emitted in the UV. The UV/FUV continuum in
AGN excites not only the emission lines in the immediate surrounding but it is
responsible for the ionization of the intergalactic medium in the early stages
of the universe. Variability studies of the emission line profiles of AGN in
the UV give us information on the structure and kinematics of the immediate
surrounding of the central supermassive black hole as well as on its mass
itself.Comment: 29 pages, 13 figures, Ap&SS in pres
On Some New Black String Solutions in Three Dimensions
We derive several new solutions in three-dimensional stringy gravity. The
solutions are obtained with the help of string duality transformations. They
represent stationary configurations with horizons, and are surrounded by
(quasi) topologically massive Abelian gauge hair, in addition to the dilaton
and the Kalb-Ramond axion. Our analysis suggests that there exists a more
general family, where our solutions are special limits. Finally, we use the
generating technique recently proposed by Garfinkle to construct a traveling
wave on the extremal variant of one of our solutions.Comment: revtex, 38 pages including 3 figure
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