8,041 research outputs found
Quantum Mechanics of the Doubled Torus
We investigate the quantum mechanics of the doubled torus system, introduced
by Hull [1] to describe T-folds in a more geometric way. Classically, this
system consists of a world-sheet Lagrangian together with some constraints,
which reduce the number of degrees of freedom to the correct physical number.
We consider this system from the point of view of constrained Hamiltonian
dynamics. In this case the constraints are second class, and we can quantize on
the constrained surface using Dirac brackets. We perform the quantization for a
simple T-fold background and compare to results for the conventional
non-doubled torus system. Finally, we formulate a consistent supersymmetric
version of the doubled torus system, including supersymmetric constraints.Comment: 31 pages, 1 figure; v2: references added, minor corrections to final
sectio
New Gauged N=8, D=4 Supergravities
New gaugings of four dimensional N=8 supergravity are constructed, including
one which has a Minkowski space vacuum that preserves N=2 supersymmetry and in
which the gauge group is broken to . Previous gaugings used the
form of the ungauged action which is invariant under a rigid symmetry
and promoted a 28-dimensional subgroup ( or the
non-semi-simple contraction ) to a local gauge group. Here, a
dual form of the ungauged action is used which is invariant under
instead of and new theories are obtained by gauging 28-dimensional
subgroups of . The gauge groups are non-semi-simple and are different
real forms of the groups, denoted , and the new
theories have a rigid SU(2) symmetry. The five dimensional gauged N=8
supergravities are dimensionally reduced to D=4. The gauge
theories reduce, after a duality transformation, to the
gauging while the gauge theory reduces to the gauge
theory. The new theories are related to the old ones via an analytic
continuation. The non-semi-simple gaugings can be dualised to forms with
different gauge groups.Comment: 33 pages. Reference adde
Consistent reductions of IIB*/M* theory and de Sitter supergravity
We construct consistent non-linear Kaluza Klein reduction ansatze for a
subset of fields arising from the reduction of IIB* and M* theory on dS_5 x H^5
and dS_4 x AdS_7, respectively. These reductions yield four and
five-dimensional de Sitter supergravities, albeit with wrong sign kinetic
terms. We also demonstrate that the ansatze may be used to lift multi-centered
de Sitter black hole solutions to ten and eleven dimensions. The lifted dS_5
black holes correspond to rotating E4-branes of IIB* theory.Comment: 27 pages, late
Generalised Geometry for M-Theory
Generalised geometry studies structures on a d-dimensional manifold with a
metric and 2-form gauge field on which there is a natural action of the group
SO(d,d). This is generalised to d-dimensional manifolds with a metric and
3-form gauge field on which there is a natural action of the group .
This provides a framework for the discussion of M-theory solutions with flux. A
different generalisation is to d-dimensional manifolds with a metric, 2-form
gauge field and a set of p-forms for either odd or even on which there is a
natural action of the group . This is useful for type IIA or IIB
string solutions with flux. Further generalisations give extended tangent
bundles and extended spin bundles relevant for non-geometric backgrounds.
Special structures that arise for supersymmetric backgrounds are discussed.Comment: 31 page
T-duality in the weakly curved background
We consider the closed string propagating in the weakly curved background
which consists of constant metric and Kalb-Ramond field with infinitesimally
small coordinate dependent part. We propose the procedure for constructing the
T-dual theory, performing T-duality transformations along coordinates on which
the Kalb-Ramond field depends. The obtained theory is defined in the
non-geometric double space, described by the Lagrange multiplier and
its -dual . We apply the proposed T-duality procedure to the
T-dual theory and obtain the initial one. We discuss the standard relations
between T-dual theories that the equations of motion and momenta modes of one
theory are the Bianchi identities and the winding modes of the other
D=6, N=2, F(4)-Supergravity with supersymmetric de Sitter Background
We show that there exists a supersymmetric de Sitter background for the D=6,
N=2, F(4) supergravity preserving the compact R-symmetry and gauging with
respect to the conventional Anti de Sitter version of the theory. We construct
the gauged matter coupled F(4) de Sitter supergravity explicitly and show that
it contains ghosts in the vector sector.Comment: 19 pages, Late
Spiral cracks in drying precipitates
We investigate the formation of spiral crack patterns during the desiccation
of thin layers of precipitates in contact with a substrate. This
symmetry-breaking fracturing mode is found to arise naturally not from torsion
forces, but from a propagating stress front induced by the fold-up of the
fragments. We model their formation mechanism using a coarse-grain model for
fragmentation and successfully reproduce the spiral cracks. Fittings of
experimental and simulation data show that the spirals are logarithmic,
corresponding to constant deviation from a circular crack path. Theoretical
aspects of the logarithmic spirals are discussed. In particular we show that
this occurs generally when the crack speed is proportional to the propagating
speed of stress front.Comment: 4 pages, 5 figures, RevTe
Supersymmetric Balance of Forces and Condensation of BPS States
Until now all known static multi black hole solutions described BPS states
with charges of the same sign. Such solutions could not be related to flat
directions in the space of BPS states. The total number of such states could
not spontaneously increase because of the charge conservation. We show that
there exist static BPS configurations which remain in equilibrium even if they
consist of states with opposite electric (or magnetic) charges from vector
multiplets. This is possible because of the exact cancellation between the
Coulomb and scalar forces. In particular, in the theories with N=4 or N=2
supersymmetry there exist stable massless multi center configurations with
vanishing total charge. Since such configurations have vanishing energy and
charge independently of their number, they can be associated with flat
directions in the space of all possible BPS states. For N=2 case this provides
a realization of the idea that BPS condensates could relate to each other
different vacua of the string theory.Comment: 19 pages, LaTe
Basal Lamina at the Epithelial-Connective Tissue Junction in the Rat Forestomach, Esophagus, Tongue and Palate: Scanning Electron Microscopic Study
The squamous epithelium lining the rat foregut was removed by incubating fresh, unfixed specimens in 2N sodium bromide. The surface morphology of the exposed subepithelial basal lamina was examined by scanning electron microscopy. Areas examined included hard and soft palates, oropharynx, tongue, esophagus, and forestomach. The basal lamina was continuous over all surfaces. Basal lamina corrugations were not present at all sites. The saucer-like defects of lymphocyte migration that are present in the basal lamina beneath the squamous epithelium of the skin were not observed in rat foregut. The epithelial-connective tissue interface of the rat esophagus does not have the coiled and branched papiIlae seen in esophagi of adult humans. The three dimensional shapes of the connective tissue cores of the various Iingual papillae are welI-demonstrated by this technique and are distinct. The basal lamina of the hard and soft palates are also distinct
Nongeometry, Duality Twists, and the Worldsheet
In this paper, we use orbifold methods to construct nongeometric backgrounds,
and argue that they correspond to the spacetimes discussed in \cite{dh,wwf}.
More precisely, we make explicit through several examples the connection
between interpolating orbifolds and spacetime duality twists. We argue that
generic nongeometric backgrounds arising from duality twists will not have
simple orbifold constructions and then proceed to construct several examples
which do have a consistent worldsheet description.Comment: v2-references added; v3-minor correction (eqn. 4.17
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