10,825 research outputs found
Black Hole Geometries in Noncommutative String Theory
We obtain a generalized Schwarzschild (GS-) and a generalized
Reissner-Nordstrom (GRN-) black hole geometries in (3+1)-dimensions, in a
noncommutative string theory. In particular, we consider an effective theory of
gravity on a curved -brane in presence of an electromagnetic (EM-) field.
Two different length scales, inherent in its noncommutative counter-part, are
exploited to obtain a theory of effective gravity coupled to an U(1)
noncommutative gauge theory to all orders in . It is shown that the
GRN-black hole geometry, in the Planckian regime, reduces to the GS-black hole.
However in the classical regime it may be seen to govern both
Reissner-Nordstrom and Schwarzschild geometries independently. The emerging
notion of 2D black holes evident in the frame-work are analyzed. It is argued
that the -string in the theory may be described by the near horizon 2D black
hole geometry, in the gravity decoupling limit. Finally, our analysis explains
the nature of the effective force derived from the nonlinear EM-field and
accounts for the Hawking radiation phenomenon in the formalism.Comment: 30 pages, 2 figure
The Generalised Raychaudhuri Equations : Examples
Specific examples of the generalized Raychaudhuri Equations for the evolution
of deformations along families of dimensional surfaces embedded in a
background dimensional spacetime are discussed. These include string
worldsheets embedded in four dimensional spacetimes and two dimensional
timelike hypersurfaces in a three dimensional curved background. The issue of
focussing of families of surfaces is introduced and analysed in some detail.Comment: 8 pages (Revtex, Twocolumn format). Corrected(see section on string
worldsheets), reorganised and shortened slightl
Path integrals and wavepacket evolution for damped mechanical systems
Damped mechanical systems with various forms of damping are quantized using
the path integral formalism. In particular, we obtain the path integral kernel
for the linearly damped harmonic oscillator and a particle in a uniform
gravitational field with linearly or quadratically damped motion. In each case,
we study the evolution of Gaussian wavepackets and discuss the characteristic
features that help us distinguish between different types of damping. For
quadratic damping, we show that the action and equation of motion of such a
system has a connection with the zero dimensional version of a currently
popular scalar field theory. Furthermore we demonstrate that the equation of
motion (for quadratic damping) can be identified as a geodesic equation in a
fictitious two-dimensional space.Comment: 15 pages, 6 figure
Interpretative Bias: Indicators of Cognitive Vulnerability to Depression
Objectives: The study aimed at testing the existence of interpretative bias in remitted depressives as compared to unipolar depressives and never-depressed individuals. Method: Cognitive Bias Questionnaire was administered on 10 individuals each with unipolar depression, remitted depression, and never-depressed participants. Participants were presented with vague and ambiguous vignettes of potentially problematic situation that individuals often encounter their daily lives. Each vignette is followed by four questions with four response options reflecting a depressed-distorted, depressed-nondistorted, nondepressed-distorted, or nondepressed- nondistorted option. Participants choose the response option that best represents how they would respond to the situation if it actually happened to them. Results: Unipolar depressives interpret their condition as high on depressive mood symptoms as well as distorted thoughts whereas remitted depressives interpret their condition as high on distorted thoughts alone. Conclusions: It may suggest that despite of reduction in level of symptomatic severity of depression, cognitive errors are still maintained during remission, can increase one’s vulnerability for relapse. It implies that management of depression should focus on reducing cognitive vulnerability to depression, rather than only targeting a reduction in the symptoms
Interaction of D-string with F-string: A Path-Integral Formalism
A path integral formalism is developed to study the interaction of an
arbitrary curved Dirichlet (D-) string with elementary excitations of the
fundumental (F-) string in bosonic string theory. Up to the next to leading
order in the derivative expansion, we construct the properly renormalized
vertex operator, which generalizes the one previously obtained for a D-particle
moving along a curved trajectory. Using this vertex, an attempt is further made
to quantize the D-string coordinates and to compute the quantum amplitude for
scattering between elementary excitations of the D- and F-strings. By studying
the dependence on the Liouville mode for the D-string, it is found that the
vertex in our approximation consists of an infinite tower of local vertex
operators which are conformally invariant on their respective mass-shell. This
analysis indicates that, unlike the D-particle case, an off-shell extension of
the interaction vertex would be necessary to compute the full amplitude and
that the realization of symmetry can be quite non-trivial when the dual
extended objects are simultaneously present. Possible future directions are
suggested.Comment: 23 pages, latex, no figure
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