719 research outputs found
On Lorentz invariance and supersymmetry of four particle scattering amplitudes in orbifold sigma model
The supersymmetric orbifold sigma model is expected to describe the
IR limit of the Matrix string theory. In the framework of the model the type
IIA string interaction is governed by a vertex which was recently proposed by
R.Dijkgraaf, E.Verlinde and H.Verlinde. By using this interaction vertex we
derive all four particle scattering amplitudes directly from the orbifold model
in the large limit.Comment: Latex, 23 page
General Rotating Black Holes in String Theory: Greybody Factors and Event Horizons
We derive the wave equation for a minimally coupled scalar field in the
background of a general rotating five-dimensional black hole. It is written in
a form that involves two types of thermodynamic variables, defined at the inner
and outer event horizon, respectively. We model the microscopic structure as an
effective string theory, with the thermodynamic properties of the left and
right moving excitations related to those of the horizons. Previously known
solutions to the wave equation are generalized to the rotating case, and their
regime of validity is sharpened. We calculate the greybody factors and
interpret the resulting Hawking emission spectrum microscopically in several
limits. We find a U-duality invariant expression for the effective string
length that does not assume a hierarchy between the charges. It accounts for
the universal low-energy absorption cross-section in the general non-extremal
case.Comment: 33 pages, latex; minor typos corrected; version to appear in PR
Supergravity and The Large N Limit of Theories With Sixteen Supercharges
We consider field theories with sixteen supersymmetries, which includes U(N)
Yang-Mills theories in various dimensions, and argue that their large N limit
is related to certain supergravity solutions. We study this by considering a
system of D-branes in string theory and then taking a limit where the brane
worldvolume theory decouples from gravity. At the same time we study the
corresponding D-brane supergravity solution and argue that we can trust it in
certain regions where the curvature (and the effective string coupling, where
appropriate) are small. The supergravity solutions typically have several
weakly coupled regions and interpolate between different limits of
string-M-theory.Comment: 24 pages, latex. v2: reference added, v3: typos correcte
Direct Integration of the Topological String
We present a new method to solve the holomorphic anomaly equations governing
the free energies of type B topological strings. The method is based on direct
integration with respect to the non-holomorphic dependence of the amplitudes,
and relies on the interplay between non-holomorphicity and modularity
properties of the topological string amplitudes. We develop a formalism valid
for any Calabi-Yau manifold and we study in detail two examples, providing
closed expressions for the amplitudes at low genus, as well as a discussion of
the boundary conditions that fix the holomorphic ambiguity. The first example
is the non-compact Calabi-Yau underlying Seiberg-Witten theory and its
gravitational corrections. The second example is the Enriques Calabi-Yau, which
we solve in full generality up to genus six. We discuss various aspects of this
model: we obtain a new method to generate holomorphic automorphic forms on the
Enriques moduli space, we write down a new product formula for the fiber
amplitudes at all genus, and we analyze in detail the field theory limit. This
allows us to uncover the modularity properties of SU(2), N=2 super Yang-Mills
theory with four massless hypermultiplets.Comment: 75 pages, 3 figure
When to perform urodynamics before mid-urethral sling surgery for female stress urinary incontinence?
INTRODUCTION AND HYPOTHESIS: Development of a model that can predict in which group of women pre-operative urodynamics can be safely omitted. METHODS: Three hundred and eighty-one uncomplicated women who underwent pre-operative urodynamics were evaluated. A multivariate logistic regression model was developed based on medical history and physical examination predicting a high probability group of women with detrusor overactivity or a low (<20 cm H2O) mean urethral closure pressure and, therefore, are likely to benefit from urodynamics. RESULTS: Women are likely to benefit from pre-operative urodynamics if they (1) are 53 years of age or older or (2) have a history of prior incontinence surgery and are at least 29 years of age or (3) have nocturia complaints and are at least 36 years of age. CONCLUSION: If urogynaecologists omitted pre-operative urodynamics in women in the low probability group, in our population, pre-operative urodynamics would be reduced by 29
Superfield theory and supermatrix model
We study the noncommutative superspace of arbitrary dimensions in a
systematic way. Superfield theories on a noncommutative superspace can be
formulated in two folds, through the star product formalism and in terms of the
supermatrices. We elaborate the duality between them by constructing the
isomorphism explicitly and relating the superspace integrations of the star
product Lagrangian or the superpotential to the traces of the supermatrices. We
show there exists an interesting fine tuned commutative limit where the duality
can be still maintained. Namely on the commutative superspace too, there exists
a supermatrix model description for the superfield theory. We interpret the
result in the context of the wave particle duality. The dual particles for the
superfields in even and odd spacetime dimensions are D-instantons and D0-branes
respectively to be consistent with the T-duality.Comment: 1+16 pages, no figure; expanded version, references added; Convention
for Clifford algebra improve
Superpotentials from flux compactifications of M-theory
In flux compactifications of M-theory a superpotential is generated whose
explicit form depends on the structure group of the 7-dimensional internal
manifold. In this note, we discuss superpotentials for the structure groups:
G_2, SU(3) or SU(2). For the G_2 case all internal fluxes have to vanish. For
SU(3) structures, the non-zero flux components entering the superpotential
describe an effective 1-dimensional model and a Chern-Simons model if there are
SU(2) structures.Comment: 10 page
Magnetically charged solutions via an analog of the electric-magnetic duality in (2+1)-dimensional gravity theories
We find an analog of the electric-magnetic duality, which is a
transformation between magnetic and electric sectors of the static and
rotationally symmetric solutions in a class of (2+1)-dimensional
Einstein-Maxwell-Dilaton gravity theories. The theories in our consideration
include, in particular, one parameter class of theories continuously connecting
the Banados-Teitelboim-Zanelli (BTZ) gravity and the low energy string
effective theory. When there is no charge, we have or
symmetry, depending on a parameter that specifies each theory. Via the
transformation, we obtain exact magnetically charged solutions from the known
electrically charged solutions. We explain the relationship between the
transformation and symmetry, and comment on the -duality of the
string theory.Comment: 10 pages, RevTe
Matrix Black Holes
Four and five dimensional extremal black holes with nonzero entropy have
simple presentations in M-theory as gravitational waves bound to configurations
of intersecting M-branes. We discuss realizations of these objects in matrix
models of M-theory, investigate the properties of zero-brane probes, and
propose a measure of their internal density. A scenario for black hole dynamics
is presented.Comment: 26 pages, harvmac; a few more references and additional comment
Comments on Black Holes in Matrix Theory
The recent suggestion that the entropy of Schwarzschild black holes can be
computed in matrix theory using near-extremal D-brane thermodynamics is
examined. It is found that the regime in which this approach is valid actually
describes black strings stretched across the longitudinal direction, near the
transition where black strings become unstable to the formation of black holes.
It is argued that the appropriate dynamics on the other (black hole) side of
the transition is that of the zero modes of the corresponding super Yang-Mills
theory. A suggestive mean field theory argument is given for the entropy of
black holes in all dimensions. Consequences of the analysis for matrix theory
and the holographic principle are discussed.Comment: 15 pages, harvmac, minor errors correcte
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