655 research outputs found
ATM-CMG control system stability
Stability analyses and simulation data and results are presented for an initial Control Moment Gyroscope system proposed for the Apollo Telescope Mount cluster (later named Skylab) using momentum vector feedback. A compensation filtering technique is presented which significantly improved analytical and simulation performance of the system. This technique is quite similar to the complementary filtering technique and represents an early NASA application
Quantisation of Conformal Fields in Three-dimensional Anti-de Sitter Black Hole Spacetime
Utilizing the conformal-flatness nature of 3-dim. Anti-de Sitter (AdS_3)
black hole solution of Banados, Teitelboim and Zanelli, the quantisation of
conformally-coupled scalar and spinor fields in this background spacetime is
explicitly carried out. In particular, mode expansion forms and propagators of
the fields are obtained in closed forms. The vacuum in this conformally-coupled
field theories in AdS_3 black hole spacetime, which is conformally-flat, is the
conformal vacuum which is unique and has global meaning. This point
particularly suggests that now the particle production by AdS_3 black hole
spacetime should be absent. General argument establishing the absence of real
particle creation by AdS_3 black hole spacetime for this case of conformal
triviality is provided. Then next, using the explicit mode expansion forms for
conformally-coupled scalar and spinor fields, the bosonic and fermionic
superradiances are examined and found to be absent confirming the expectation.Comment: 51 pages, Revtex, version to appear in Int. J. Mod. Phys.
Back-reaction of a conformal field on a three-dimensional black hole
The first order corrections to the geometry of the (2+1)-dimensional black
hole due to back-reaction of a massless conformal scalar field are computed.
The renormalized stress energy tensor used as the source of Einstein equations
is computed with the Green function for the black-hole background with
transparent boundary conditions. This tensor has the same functional form as
the one found in the nonperturbative case which can be exactly solved. Thus, a
static, circularly symmetric and asymptotically anti-de Sitter black hole
solution of the semiclassical equations is found. The corrections to the
thermodynamic quantities are also computed.Comment: 12 pages, RevTeX, no figure
Non-Extreme and Ultra-Extreme Domain Walls and Their Global Space-Times
Non-extreme walls (bubbles with two insides) and ultra-extreme walls (bubbles
of false vacuum decay) are discussed. Their respective energy densities are
higher and lower than that of the corresponding extreme (supersymmetric),
planar domain wall. These singularity free space-times exhibit non-trivial
causal structure analogous to certain non-extreme black holes. We focus on
anti-de~Sitter--Minkowski walls and comment on Minkowski--Minkowski walls with
trivial extreme limit, as well as walls adjacent to de~Sitter space-times with
no extreme limit.Comment: Revised version, 4 pages of REVTEX, UPR-546-T/Rev. Two figures not
included. This version contains further elaboration of the space-time causal
structur
Entropy of scalar fields in 3+1 dimensional constant curvature black hole background
We consider the thermodynamics of minimally coupled massive scalar field in
3+1 dimensional constant curvature black hole background. The brick wall model
of 't Hooft is used. When Scharzschild like coordinates are used it is found
that apart from the usual radial brick wall cut-off parammeter an angular
cut-off parameter is required to regularize the solution. Free energy of the
scalar field is obtained through counting of states using the WKB
approximation. It is found that the free energy and the entropy are
logarithmically divergent in both the cut-off parameters.Comment: 9 pages, LaTe
Thermodynamics and Evaporation of the 2+1-D Black Hole
The properties of canonical and microcanonical ensembles of a black hole with
thermal radiation and the problem of black hole evaporation in 3-D are studied.
In 3-D Einstein-anti-de Sitter gravity we have two relevant mass scales,
, and , which are particularly relevant
for the evaporation problem. It is argued that in the `weak coupling' regime
, the end point of an evaporating black hole formed
with an initial mass , is likely to be a stable remnant in equilibrium
with thermal radiation. The relevance of these results for the information
problem and for the issue of back reaction is discussed. In the `strong
coupling' regime, a full fledged quantum gravity
treatment is required. Since the total energy of thermal states in anti-de
Sitter space with reflective boundary conditions at spatial infinity is bounded
and conserved, the canonical and microcanonical ensembles are well defined. For
a given temperature or energy black hole states are locally stable. In the weak
coupling regime black hole states are more probable then pure radiation states.Comment: 11 pages, TAUP 2141/94, Late
Scalar field quantization on the 2+1 dimensional black hole background
The quantization of a massless conformally coupled scalar field on the 2+1
dimensional Anti de Sitter black hole background is presented. The Green's
function is calculated, using the fact that the black hole is Anti de Sitter
space with points identified, and taking into account the fact that the black
hole spacetime is not globally hyperbolic. It is shown that the Green's
function calculated in this way is the Hartle-Hawking Green's function. The
Green's function is used to compute , which is
regular on the black hole horizon, and diverges at the singularity. A particle
detector response function outside the horizon is also calculated and shown to
be a fermi type distribution. The back-reaction from is calculated exactly and is shown to give rise to a curvature
singularity at and to shift the horizon outwards. For a horizon
develops, shielding the singularity. Some speculations about the endpoint of
evaporation are discussed.Comment: CTP 2243, 24 pages, RevTex. (The backreaction section is extended,
and some confusing notation has been changed
Anti-de Sitter Supersymmetry
We give a pedagogical introduction to certain aspects of supersymmetric field
theories in anti-de Sitter space. Among them are the presence of masslike terms
in massless wave equations, irreducible unitary representations and the
phenomenon of multiplet shortening.Comment: Lectures presented by B. de Wit at the Winter School of Theoretical
Physics, Polanica, Poland, February 1999. 23 pp., LateX file, requires
packages latexsym, amsfonts, cl2emult.cl
Antiperiodic solitons of the Goldstone model on S^1
Our purpose is to present all static solutions of the Goldstone model on a
circle in 1+1 dimensions with an antiperiodicity condition imposed on the
scalar fields. Jacobi elliptic and standard trigonometric functions are used to
express the solutions found and stability analysis of the latter is what
follows. Classically stable quasi-topological solitons are identified.Comment: 12 pages, 3 figures, 3 references added, some corrections made.
Accepted for publication in Nonlinearit
Brick Walls and AdS/CFT
We discuss the relationship between the bulk-boundary correspondence in
Rehren's algebraic holography (and in other 'fixed-background' approaches to
holography) and in mainstream 'Maldacena AdS/CFT'. Especially, we contrast the
understanding of black-hole entropy from the viewpoint of QFT in curved
spacetime -- in the framework of 't Hooft's 'brick wall' model -- with the
understanding based on Maldacena AdS/CFT. We show that the brick-wall
modification of a Klein Gordon field in the Hartle-Hawking-Israel state on
1+2-Schwarzschild AdS (BTZ) has a well-defined boundary limit with the same
temperature and entropy as the brick-wall-modified bulk theory. One of our main
purposes is to point out a close connection, for general AdS/CFT situations,
between the puzzle raised by Arnsdorf and Smolin regarding the relationship
between Rehren's algebraic holography and mainstream AdS/CFT and the puzzle
embodied in the 'correspondence principle' proposed by Mukohyama and Israel in
their work on the brick-wall approach to black hole entropy. Working on the
assumption that similar results will hold for bulk QFT other than the Klein
Gordon field and for Schwarzschild AdS in other dimensions, and recalling the
first author's proposed resolution to the Mukohyama-Israel puzzle based on his
'matter-gravity entanglement hypothesis', we argue that, in Maldacena AdS/CFT,
the algebra of the boundary CFT is isomorphic only to a proper subalgebra of
the bulk algebra, albeit (at non-zero temperature) the (GNS) Hilbert spaces of
bulk and boundary theories are still the 'same' -- the total bulk state being
pure, while the boundary state is mixed (thermal). We also argue from the
finiteness of its boundary (and hence, on our assumptions, also bulk) entropy
at finite temperature, that the Rehren dual of the Maldacena boundary CFT
cannot itself be a QFT and must, instead, presumably be something like a string
theory.Comment: 54 pages, 3 figures. Arguments strengthened in the light of B.S. Kay
`Instability of Enclosed Horizons' arXiv:1310.739
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