11,594 research outputs found
Generalized Dirichlet Branes and Zero-modes
We investigate the effective dynamics of an arbitrary Dirichlet p-brane, in a
path-integral formalism, by incorporating the massless excitations of closed
string modes in open bosonic string theory. It is shown that the closed string
background fields in the bosonic sector of type II theories induce invariant
extrinsic curvature on the world-volume. In addition, the curvature can be seen
to be associated with a divergence at the boundary of string world-sheet. The
re-normalization of the collective coordinates, next to leading order in its
derivative expansion, is performed to handle the divergence and the effective
dynamics is encoded in Dirac-Born-Infeld action. Furthermore, the collective
dynamics is generalized to include appropriate fermionic partners in type I
super-string theory. The role of string modes is reviewed in terms of the
collective coordinates and the gauge theory on the world-volume is argued to be
non-local in presence of the U(1) invariant field strength.Comment: LaTex, 20 pages, v2: minor changes and added references v3:typos
corrected, some statements are clarified in the context of zero-mode
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
Wormholes in spacetime with torsion
Analytical wormhole solutions in theory are presented. It is discussed
whether the extremely short range repulsive forces, related to the spin angular
momentum of matter, could be the ``carrier'' of the exoticity that threads the
wormhole throat.Comment: 10 pages revte
Hardy's nonlocality for generalized n-particle GHZ states
In this paper we extend Hardy's nonlocality proof for two spin-1/2 particles
[PRL 71 (1993) 1665] to the case of n spin-1/2 particles configured in the
generalized GHZ state. We show that, for all n \geq 3, any entangled GHZ state
violates the Bell inequality associated with the Hardy experiment. This feature
is important since it has been shown [PRL 88 (2002) 210402] that, for all n
odd, there are entangled GHZ states that do not violate any standard n-particle
correlation Bell inequality.Comment: LaTeX file, 8 pages, 2 eps figures; journal versio
Smooth double barriers in quantum mechanics
Quantum mechanical tunneling across smooth double barrier potentials modeled
using Gaussian functions, is analyzed numerically and by using the WKB
approximation. The transmission probability, resonances as a function of
incident particle energy, and their dependence on the barrier parameters are
obtained for various cases. We also discuss the tunneling time, for which we
obtain generalizations of the known results for rectangular barriers.Comment: 23 pages, 8 figures, a slightly reduced version to appear in American
Journal of Physics, references correcte
Bulk phantom fields, increasing warp factors and fermion localisation
A bulk phantom scalar field (with negative kinetic energy) in a sine--Gordon
type potential is used to generate an exact thick brane solution with an
increasing warp factor. It is shown that the growing nature of the warp factor
allows the localisation of massive as well as massless spin-half fermions on
the brane even without any additional non--gravitational interactions. The
exact solutions for the localised massive fermionic modes are presented and
discussed. The inclusion of a fermion--scalar Yukawa coupling appears to change
the mass spectrum and wave functions of the localised fermion though it does
not play the crucial role it did in the case of a decreasing warp factor.Comment: 11 pages, 3 figures, RevTex
Static and dynamic traversable wormhole geometries satisfying the Ford-Roman constraints
It was shown by Ford and Roman in 1996 that quantum field theory severely
constrains wormhole geometries on a macroscopic scale. The first part of this
paper discusses a wide class of wormhole solutions that meet these constraints.
The type of shape function used is essentially generic. The constraints are
then discussed in conjunction with various redshift functions. Violations of
the weak energy condition and traversability criteria are also considered. The
second part of the paper analyzes analogous time-dependent (dynamic) wormholes
with the aid of differential forms. It is shown that a violation of the weak
energy condition is not likely to be avoidable even temporarily.Comment: 16 pages AMSTe
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