4,322 research outputs found
Multiplet Structures of BPS Solitons
There exist simple single-charge and multi-charge BPS p-brane solutions in
the D-dimensional maximal supergravities. From these, one can fill out orbits
in the charge vector space by acting with the global symmetry groups. We give a
classification of these orbits, and the associated cosets that parameterise
them.Comment: Latex, 34 pages, comments and reference adde
BRST Quantisation of the N=2 String in a Real Spacetime Structure
We study the string with a real structure on the spacetime,
using BRST methods. Several new features emerge. In the diagonal basis, the
operator , which is associated with the
moduli for the gauge field on the world-sheet, is local and it relates
the physical operators in the NS and R sectors. However, the picture-changing
operators are non-invertible in this case, and physical operators in different
pictures cannot be identified. The three-point interactions of all physical
operators leads to three different types of amplitudes, which can be
effectively described by the interactions of a scalar NS operator and a bosonic
spinorial R operator. In the off-diagonal bases for the fermionic currents, the
picture-changing operators are invertible, and hence physical operators in
different pictures can be identified. However, now there is no local operator
that relates the physical operators in
different sectors. The physical spectrum is thus described by one scalar NS
operator and one spinorial R operator. The NS and R operators give rise to
different types of three-point amplitudes, and thus cannot be identified.Comment: 17 pages, latex, no figures. Significant revisions, with extended
discussion of cohomology in different bases for fermionic current
On Black Hole Stability in Critical Gravities
We consider extended cosmological gravities with Ricci tensor and scalar
squared terms in diverse dimensions. These theories admit solutions of Einstein
metrics, including the Schwarzschild-Tangherlini AdS black holes, whose mass
and entropy vanish at the critical point. We perform linearized analysis around
the black holes and show that in general the spectrum consists of the usual
spin-2 massless and ghost massive modes. We demonstrate that there is no
exponentially-growing tachyon mode in the black holes. At the critical point,
the massless spin-2 modes have zero energy whilst the massive spin-2 modes are
replaced by the log modes. There always exist certain linear combination of
massless and log modes that has negative energy. Thus the stability of the
black holes requires that the log modes to be truncated out by the boundary
condition.Comment: 16 pages, minor corrections, further comments and references adde
Intersecting M-branes and bound states
In this paper, we construct multi-scalar, multi-center -brane solutions in
toroidally compactified M-theory. We use these solutions to show that all
supersymmetric -branes can be viewed as bound states of certain basic
building blocks, namely -branes that preserve of the supersymmetry. We
also explore the M-theory interpretation of -branes in lower dimensions. We
show that all the supersymmetric -branes can be viewed as intersections of
M-branes or boosted M-branes in .Comment: Latex, 14 pages, no figures. References adde
Vertical versus Diagonal Dimensional Reduction for p-branes
In addition to the double-dimensional reduction procedure that employs
world-volume Killing symmetries of -brane supergravity solutions and acts
diagonally on a plot of versus spacetime dimension , there exists a
second procedure of ``vertical'' reduction. This reduces the transverse-space
dimension via an integral that superposes solutions to the underlying Laplace
equation. We show that vertical reduction is also closely related to the
recently-introduced notion of intersecting -branes. We illustrate this with
examples, and also construct a new solution describing four intersecting
membranes, which preserves of the supersymmetry. Given the two reduction
schemes plus duality transformations at special points of the scalar modulus
space, one may relate most of the -brane solutions of relevance to
superstring theory. We argue that the maximum classifying duality symmetry for
this purpose is the Weyl group of the corresponding Cremmer-Julia supergravity
symmetry . We also discuss a separate class of duality-invariant
-branes with .Comment: Latex, 21 pages, no figures. References adde
Gauged Kaluza-Klein AdS Pseudo-supergravity
We obtain the pseudo-supergravity extension of the D-dimensional Kaluza-Klein
theory, which is the circle reduction of pure gravity in D+1 dimensions. The
fermionic partners are pseudo-gravitino and pseudo-dilatino. The full
Lagrangian is invariant under the pseudo-supersymmetric transformation, up to
quadratic order in fermion fields. We find that the theory possesses a U(1)
global symmetry that can be gauged so that all the fermions are charged under
the Kaluza-Klein vector. The gauging process generates a scalar potential that
has a maximum, leading to the AdS vacuum. Whist the highest dimension for
gauged AdS supergravity is seven, our gauged AdS pseudo-supergravities can
exist in arbitrary dimensions.Comment: Latex, 13 pages, typos corrected, version in PL
Calabi-Yau (p+1)-folds from p-folds
We establish the general formalism for constructing metrics of Calabi-Yau
(p+1)-folds in terms of that of a p-fold by adding a complex-line bundle. We
present a few explicit low-lying examples. We further consider holomorphic
linearization and obtain the six-dimensional analogue of the Gibbons-Hawking
instanton. Whilst the Kahler potential for the Gibbons-Hawking instanton is
given by the harmonic function of a three-dimensional flat space, for the
generalized solution it is related to the harmonic functions of certain
three-dimensional non-flat spaces that are direct products of R and
two-dimensional Kahler spaces.Comment: 21 pages, no figure
A flexible mandatory access control policy for XML databases
A flexible mandatory access control policy (MAC) for XML
databases is presented in this paper. The label type and label
access policy can be defined according to the requirements of
applications. In order to preserve the integrity of data in XML
databases, a constraint between a read access rule and a write
access rule in label access policy is introduced. Rules for label
assignment and propagation are proposed to alleviate the
workload of label assignment. Also, a solution for resolving
conflicts of label assignments is proposed. At last, operations for
implementation of the MAC policy in a XML database are
illustrated
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