1,579 research outputs found
Duality, Marginal Perturbations and Gauging
We study duality transformations for two-dimensional sigma models with
abelian chiral isometries and prove that generic such transformations are
equivalent to integrated marginal perturbations by bilinears in the chiral
currents, thus confirming a recent conjecture by Hassan and Sen formulated in
the context of Wess-Zumino-Witten models. Specific duality transformations
instead give rise to coset models plus free bosons.Comment: 15 page
Black-Hole-Wave Duality in String Theory
Extreme 4-dimensional dilaton black holes embedded into 10-dimensional
geometry are shown to be dual to the gravitational waves in string theory. The
corresponding gravitational waves are the generalization of pp-fronted waves,
called supersymmetric string waves. They are given by Brinkmann metric and the
two-form field, without a dilaton. The non-diagonal part of the metric of the
dual partner of the wave together with the two-form field correspond to the
vector field in 4-dimensional geometry of the charged extreme black holes.Comment: 12 pages, LaTeX, preprint UG-3/94, SU-ITP-94-11, QMW-PH-94-1
T-duality of anomalous Chern-Simons couplings
It is known that the anomalous D-brane Chern-Simons couplings are not
consistent with the standard rules of T-duality. Using compatibility of these
couplings with the linear T-duality transformations, the B-field gauge
transformations and with the general coordinate transformations as guiding
principles we find new couplings at order for , , and .Comment: 19 pages, Latex file, no figure, the version appears in NP
Abelian duality in WZW models
We analyse abelian T-duality for WZW models of simply-connected groups. We
demonstrate that the dual theory is a certain orbifold of the original theory,
and check that it is conformally invariant. We determine the spectrum of the
dual theory, and show that it agrees with the spectrum of the original theory.Comment: 15 pages, late
Branes, Times and Dualities
Dualities link M-theory, the 10+1 dimensional strong coupling limit of the
IIA string, to other 11-dimensional theories in signatures 9+2 and 6+5, and to
type II string theories in all 10-dimensional signatures. We study the
Freund-Rubin-type compactifications and brane-type solutions of these theories,
and find that branes with various world-volume signatures are possible. For
example, the 9+2 dimensional M* theory has membrane-type solutions with
world-volumes of signature (3,0) and (1,2), and a solitonic solution with
world-volume signature (5,1).Comment: 36 pages, 4 Postscript figures, uses harvmac macr
Duality Versus Supersymmetry and Compactification
We study the interplay between T-duality, compactification and supersymmetry.
We prove that when the original configuration has unbroken space-time
supersymmetries, the dual configuration also does if a special condition is
met: the Killing spinors of the original configuration have to be independent
on the coordinate which corresponds to the isometry direction of the bosonic
fields used for duality. Examples of ``losers" (T-duals are not supersymmetric)
and ``winners" (T-duals are supersymmetric) are given.Comment: LaTeX file, 19 pages, U. of Groningen Report UG-8/94, Stanford U.
Report SU-ITP-94-19, QMW College Report QMW-PH-94-1
A Closed, Expanding Universe in String Theory
We present a conformal field theory -- obtained from a gauged WZW model --
that describes a closed, inhomogeneous expanding and recollapsing universe in
dimensions. A possible violation of cosmic censorship is avoided because
the universe recollapses just when a naked singularity was about to form. The
model has been chosen to have (or in the supersymmetric
case), just like four dimensional Minkowski space.Comment: 10 p
Type 0 T-Duality and the Tachyon Coupling
We consider the T-duality relations between Type 0A and 0B theories, and show
that this constraints the possible couplings of the tachyon to the RR-fields.
Due to the `doubling' of the RR sector in Type 0 theories, we are able to
introduce a democratic formulation for the Type 0 effective actions, in which
there is no Chern-Simons term in the effective action. Finally we discuss how
to embed Type II solutions into Type 0 theories.Comment: some misprints corrected and a reference adde
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Augmented design for a fully automated alignment system at the Magdalena Ridge Observatory Interferometer
Michelson Interferometry with the Keck I Telescope
We report the first use of Michelson interferometry on the Keck I telescope
for diffraction-limited imaging in the near infrared JHK and L bands. By using
an aperture mask located close to the f/25 secondary, the 10 m Keck primary
mirror was transformed into a separate-element, multiple aperture
interferometer. This has allowed diffraction-limited imaging of a large number
of bright astrophysical targets, including the geometrically complex dust
envelopes around a number of evolved stars. The successful restoration of these
images, with dynamic ranges in excess of 200:1, highlights the significant
capabilities of sparse aperture imaging as compared with more conventional
filled-pupil speckle imaging for the class of bright targets considered here.
In particular the enhancement of the signal-to-noise ratio of the Fourier data,
precipitated by the reduction in atmospheric noise, allows high fidelity
imaging of complex sources with small numbers of short-exposure images relative
to speckle. Multi-epoch measurements confirm the reliability of this imaging
technique and our whole dataset provides a powerful demonstration of the
capabilities of aperture masking methods when utilized with the current
generation of large-aperture telescopes. The relationship between these new
results and recent advances in interferometry and adaptive optics is briefly
discussed.Comment: Accepted into Publications of the Astronomical Society of the
Pacific. To appear in vol. 112. Paper contains 10 pages, 8 figure
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