425 research outputs found
CT-duality as a local property of the world-sheet
In the present article, we study the local features of the world-sheet in the
case when probe bosonic string moves in antisymmetric background field. We
generalize the geometry of surfaces embedded in space-time to the case when the
torsion is present. We define the mean extrinsic curvature for spaces with
Minkowski signature and introduce the concept of mean torsion. Its orthogonal
projection defines the dual mean extrinsic curvature. In this language, the
field equation is just the equality of mean extrinsic curvature and extrinsic
mean torsion, which we call CT-duality. To the world-sheet described by this
relation we will refer as CT-dual surface.Comment: Latex, 15 pages, 2 Figure
A class of non-singular gravi-dilaton backgrounds
We present a class of static, spherically symmetric, non-singular solutions
of the tree-level string effective action, truncated to first order in
. In the string frame the solutions approach asymptotically (at and ) two different anti-de Sitter configurations, thus
interpolating between two maximally symmetric states of different constant
curvature. The radial-dependent dilaton defines a string coupling which is
everywhere finite, with a peak value that can be chosen arbitrarily small so as
to neglect quantum-loop corrections. This example stresses the possible
importance of finite-size corrections, typical of string theory, in
avoiding space-time singularities.Comment: 9 pages, LATEX, four figure included using EPSFIG. Essay written for
the 1997 Awards of the Gravity Research Foundation, and selected for
"Honorable Mention". To appear in Mod. Phys. Lett.
One-Loop Effective Action for Spherical Scalar Field Collapse
We calculate the complete one-loop effective action for a spherical scalar
field collapse in the large radius approximation. This action gives the
complete trace anomaly, which beside the matter loop contributions, receives a
contribution from the graviton loops. Our result opens a possibility for a
systematic study of the back-reaction effects for a real black hole.Comment: 14 pages, slightly expanded version to appear in Class. Quant. Gra
The Bekenstein Formula and String Theory (N-brane Theory)
A review of recent progress in string theory concerning the Bekenstein
formula for black hole entropy is given. Topics discussed include p-branes,
D-branes and supersymmetry; the correspondence principle; the D- and M-brane
approach to black hole entropy; the D-brane analogue of Hawking radiation, and
information loss; D-branes as probes of black holes; and the Matrix theory
approach to charged and neutral black holes. Some introductory material is
included.Comment: 53 pages, LaTeX. v3: Typos fixed, minor updates, references added,
brief Note Added on AdS/CF
Topological Dilatonic Supergravity Theories
We present a central extension of the super-Poincar\'e algebra in two
dimensions. Besides the usual Poincar\'e generators and the
supersymmetry generators we have Grassmann generators, a bosonic
internal symmetry generator and a central charge. We then build up the
topological gauge theory associated to this algebra. We can solve the classical
field equations for the fields which do not belong to the supergravity
multiplet and to a Lagrange multiplier multiplet. The resulting topological
supergravity theory turns out to be non-local in the fermionic sector.Comment: 11 pages, plain TeX, IFUSP-P/112
2+1 Black Hole with a Dynamical Conical Singularity
We find black hole solutions to Euclidean 2+1 gravity coupled to a
relativistic particle which have a dynamical conical singularity at the
horizon. These solutions mimic the tree level contribution to the partition
function of gravity coupled to a quantum field theory. They are found to
violate the standard area law for black hole entropy, their entropy being
proportional to the total opening angle. Since each solution depends on the
number of windings of the particle path around the horizon, the significance of
their summation in the path integral is considered.Comment: 11 pages, LaTeX, no figures. Revised version to appear in Class.
Quant. Grav. The main changes are an expanded introduction and a better
presentation of the body of the paper. Three paragraphs have also been added
to the conclusio
Classical integrability of chiral and classical curves
In this letter, classical chiral is studied in the lightcone gauge
. The once integrated equation of motion for the current is shown to
be of the Lax form, which demonstrates an infinite number of conserved
quantities. Specializing to gauge group SU(2), we show that solutions to the
classical equations of motion can be identified with a very large class of
curves. We demonstrate this correspondence explicitly for two solutions. The
classical fermionic fields associated with these currents are then obtained.Comment: Final version to appear in Mod. Phys. Lett. A. A reference and two
footnotes added. 6 pages revte
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