1,282 research outputs found
Complexified sigma model and duality
We show that the equations of motion associated with a complexified
sigma-model action do not admit manifest dual SO(n,n) symmetry. In the process
we discover new type of numbers which we called `complexoids' in order to
emphasize their close relation with both complex numbers and matroids. It turns
out that the complexoids allow to consider the analogue of the complexified
sigma-model action but with (1+1)-worldsheet metric, instead of
Euclidean-worldsheet metric. Our observations can be useful for further
developments of complexified quantum mechanics.Comment: 15 pages, Latex, improved versio
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
Supersymmetry and Stationary Solutions in Dilaton-Axion Gravity
New stationary solutions of -dimensional dilaton-axion gravity are
presented, which correspond to the charged Taub-NUT and Israel-Wilson-Perjes
(IWP) solutions of Einstein-Maxwell theory. The charged axion-dilaton Taub-NUT
solutions are shown to have a number of interesting properties: i) manifest
symmetry, ii) an infinite throat in an extremal limit, iii) the
throat limit coincides with an exact CFT construction.
The IWP solutions are shown to admit supersymmetric Killing spinors, when
embedded in supergravity. This poses a problem for the interpretation
of supersymmetric rotating solutions as physical ground states. In the context
of -dimensional geometry, we show that dimensionally lifted versions of the
IWP solutions are dual to certain gravitational waves in string theory.Comment: 23 pages (latex), SU-ITP-94-12, UMHEP-407, QMW-PH-94-1
On the equivalence between topologically and non-topologically massive abelian gauge theories
We analyse the equivalence between topologically massive gauge theory (TMGT)
and different formulations of non-topologically massive gauge theories (NTMGTs)
in the canonical approach. The different NTMGTs studied are St\"uckelberg
formulation of (A) a first order formulation involving one and two form fields,
(B) Proca theory, and (C) massive Kalb-Ramond theory. We first quantise these
reducible gauge systems by using the phase space extension procedure and using
it, identify the phase space variables of NTMGTs which are equivalent to the
canonical variables of TMGT and show that under this the Hamiltonian also get
mapped. Interestingly it is found that the different NTMGTs are equivalent to
different formulations of TMGTs which differ only by a total divergence term.
We also provide covariant mappings between the fields in TMGT to NTMGTs at the
level of correlation function.Comment: One reference added and a typos corrected. 15 pages, To appear in
Mod. Phys. Lett.
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
N=2 Boundary conditions for non-linear sigma models and Landau-Ginzburg models
We study N=2 nonlinear two dimensional sigma models with boundaries and their
massive generalizations (the Landau-Ginzburg models). These models are defined
over either Kahler or bihermitian target space manifolds. We determine the most
general local N=2 superconformal boundary conditions (D-branes) for these sigma
models. In the Kahler case we reproduce the known results in a systematic
fashion including interesting results concerning the coisotropic A-type branes.
We further analyse the N=2 superconformal boundary conditions for sigma models
defined over a bihermitian manifold with torsion. We interpret the boundary
conditions in terms of different types of submanifolds of the target space. We
point out how the open sigma models correspond to new types of target space
geometry. For the massive Landau-Ginzburg models (both Kahler and bihermitian)
we discuss an important class of supersymmetric boundary conditions which
admits a nice geometrical interpretation.Comment: 48 pages, latex, references and minor comments added, the version to
appear in JHE
Gravitational instantons and black plane solutions in 4-d string theory
We consider gauged Wess-Zumino models based on the non compact group
. It is shown that by vector gauging the maximal compact subgroup
the resulting backgrounds obey the gravity-dilaton one loop string
vacuum equations of motion in four dimensional euclidean space. The torsionless
solution is then interpreted as a pseudo-instanton of the Liouville
theory coupled to gravity. The presence of a traslational isometry in the model
allows to get another string vacuum backgrounds by using target duality that we
identify with those corresponding to the axial gauging. We also compute the
exact backgrounds. Depending on the value of , they may be interpreted as
instantons connecting a highly singular big bang like universe with a static
singular or regular black plane geometry.Comment: 29 page
Differential geometry with a projection: Application to double field theory
In recent development of double field theory, as for the description of the
massless sector of closed strings, the spacetime dimension is formally doubled,
i.e. from D to D+D, and the T-duality is realized manifestly as a global O(D,D)
rotation. In this paper, we conceive a differential geometry characterized by a
O(D,D) symmetric projection, as the underlying mathematical structure of double
field theory. We introduce a differential operator compatible with the
projection, which, contracted with the projection, can be covariantized and may
replace the ordinary derivatives in the generalized Lie derivative that
generates the gauge symmetry of double field theory. We construct various gauge
covariant tensors which include a scalar and a tensor carrying two O(D,D)
vector indices.Comment: 1+22 pages, No figure; a previous result on 4-index tensor removed,
presentation improve
Nonsingular 2-D Black Holes and Classical String Backgrounds
We study a string-inspired classical 2-D effective field theory with {\it
nonsingular} black holes as well as Witten's black hole among its static
solutions. By a dimensional reduction, the static solutions are related to the
coset model, or more precisely its
approximation known as the 3-D charged black
string. The 2-D effective action possesses a propagating degree of freedom, and
the dynamics are highly nontrivial. A collapsing shell is shown to bounce into
another universe without creating a curvature singularity on its path, and the
potential instability of the Cauchy horizon is found to be irrelevent in that
some of the infalling observers never approach the Cauchy horizon. Finally a
nonperturbative coset metric, found and advocated by R.
Dijkgraaf et.al., is shown to be nonsingular and to coincide with one of the
charged spacetimes found above. Implications of all these geometries are
discussed in connection with black hole evaporation.Comment: 30 pages with 2 figures, harvmac, CALT-68-1852 (Discussions on the
gravitational collapse of thin shells in a charged spacetime are clarified.
Two extra references.
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