1,276 research outputs found
Decay Modes of Intersecting Fluxbranes
Just as the single fluxbrane is quantum mechanically unstable to the
nucleation of a locally charged spherical brane, so intersecting fluxbranes are
unstable to various decay modes. Each individual element of the intersection
can decay via the nucleation of a spherical brane, but uncharged spheres can
also be nucleated in the region of intersection. For special values of the
fluxes, however, intersecting fluxbranes are supersymmetric, and so are
expected to be stable. We explicitly consider the instanton describing the
decay modes of the two--element intersection (an F5-brane in the string theory
context), and show that in dimensions greater than four the action for the
decay mode of the supersymmetric intersection diverges. This observation allows
us to show that stable intersecting fluxbranes should also exist in type 0A
string theory.Comment: 19 pages, 6 figures. References adde
An Exact String Theory Model of Closed Time-Like Curves and Cosmological Singularities
We study an exact model of string theory propagating in a space-time
containing regions with closed time-like curves (CTCs) separated from a finite
cosmological region bounded by a Big Bang and a Big Crunch. The model is an
non-trivial embedding of the Taub-NUT geometry into heterotic string theory
with a full conformal field theory (CFT) definition, discovered over a decade
ago as a heterotic coset model. Having a CFT definition makes this an excellent
laboratory for the study of the stringy fate of CTCs, the Taub cosmology, and
the Milne/Misner-type chronology horizon which separates them. In an effort to
uncover the role of stringy corrections to such geometries, we calculate the
complete set of alpha' corrections to the geometry. We observe that the key
features of Taub-NUT persist in the exact theory, together with the emergence
of a region of space with Euclidean signature bounded by time-like curvature
singularities. Although such remarks are premature, their persistence in the
exact geometry is suggestive that string theory theory is able to make physical
sense of the Milne/Misner singularities and the CTCs, despite their
pathological character in General Relativity. This may also support the
possibility that CTCs may be viable in some physical situations, and may be a
natural ingredient in pre-Big-Bang cosmological scenarios.Comment: 37 pages, 4 figures. V2: discussion of computation of metric refined,
references adde
Towards a supersymmetric non-abelian Born-Infeld theory
We define an iterative procedure to obtain a non-abelian generalization of
the Born-Infeld action. This construction is made possible by the use of the
severe restrictions imposed by kappa-symmetry. We have calculated all bosonic
terms in the action up to terms quartic in the Yang-Mills field strength and
all fermion bilinear terms up to terms cubic in the field strength. Already at
this order the fermionic terms do not satisfy the symmetric trace-prescription.Comment: 9 pp. Latex, to appear in the proceedings of the Strings 2000
conferenc
Non-Abelian Giant Gravitons
We argue that the giant graviton configurations known from the literature
have a complementary, microscopical description in terms of multiple
gravitational waves undergoing a dielectric (or magnetic moment) effect. We
present a non-Abelian effective action for these gravitational waves with
dielectric couplings and show that stable dielectric solutions exist. These
solutions agree in the large limit with the giant graviton configurations
in the literature.Comment: 8 pages. Contribution to the proceedings of the RTN workshop in
Leuven, Belgium, September 200
Supergravity Duals to the Noncommutative N=4 SYM theory in the Infinite Momentum Frame
In this work the construction of supergravity duals to the noncommutative
SYM theory in the infinite momentum frame but with constant
momentum density is attempted. In the absence of the content of
noncommutativity, it has been known for some time that the previous
correspondence should be replaced by the
(with denoting the generalized Kaigorodov spacetime) correspondence
with the pp-wave propagating on the BPS brane worldvolume. Interestingly
enough, putting together the two contents, i.e., the introduction of
noncommutativity and at the same time that of the pp-wave along the brane
worldvolume, leads to quite nontrivial consequences such as the emergence of
``time-space'' noncommutativity in addition to the ``space-space''
noncommutativity in the manifold on which the dual gauge theory is defined.
Taking the gravity decoupling limit, it has been realized that for small ,
the solutions all reduce to geometry confirming our
expectation that the IR dynamics of the dual gauge theory should be unaffected
by the noncommutativity while as , the solutions start to deviate
significantly from limit indicating that the UV dynamics of
the dual gauge theory would be heavily distorted by the effect of
noncommutativity.Comment: 21 pages, Latex, One expression changed, a reference added, to appear
in Phys. Rev.
Mapping articulatory and grammatical subcomponents of fluency deficits in post-stroke aphasia
Clinical decision support improves physician guideline adherence for laboratory monitoring of chronic kidney disease: a matched cohort study
Sample graph page of relevant test results. (PDF 289ĂÂ kb
Bacterial Contamination of Blood Components
Blood for transfusion is a potential source of infection by a variety of known and unknown transmissible agents. Over the last 20 years, astounding reductions in the risk of viral infection via allogeneic blood have been achieved. As a result of this success, bacterial contamination of blood products has emerged as the greatest residual source of transfusion-transmitted disease. This paper summarizes the current status of detection, prevention, and elimination of bacteria in blood products for transfusion
On Charged Black Holes in Anti-de Sitter Space
We study the region inside the event horizon of charged black holes in five
dimensional asymptotically anti-de Sitter space, using as a probe two-sided
correlators which are dominated by spacelike geodesics penetrating the horizon.
The spacetimes we investigate include the Reissner-Nordstrom black hole and
perturbations thereof. The perturbed spacetimes can be found exactly, enabling
us to perform a local scan of the region between the inner and outer horizons.
Surprisingly, the two-sided correlators we calculate seem to be geometrically
protected from the instability of the inner horizon.Comment: 1+37 pages, 20 ps and eps figures, LaTeX. References added and
changes made to section
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