1,185 research outputs found
"Optical conductance fluctuations: diagrammatic analysis in Landauer approach and non-universal effects"
The optical conductance of a multiple scattering medium is the total
transmitted light of a diffuse incoming beam. This quantity, very analogous to
the electronic conductance, exhibits universal conductance fluctuations. We
perform a detailed diagrammatic analysis of these fluctuations. With a
Kadanoff-Baym technique all the leading diagrams are systematically generated.
A cancellation of the short distance divergencies occurs, that yields a well
behaved theory. The analytical form of the fluctuations is calculated and
applied to optical systems. Absorption and internal reflections reduce the
fluctuations significantly.Comment: 25 pages Revtex 3.0, 18 seperate postscript figure
Self-Dual Conformal Supergravity and the Hamiltonian Formulation
In terms of Dirac matrices the self-dual and anti-self-dual decomposition of
a conformal supergravity is given and a self-dual conformal supergravity theory
is developed as a connection dynamic theory in which the basic dynamic variabes
include the self-dual spin connection i.e. the Ashtekar connection rather than
the triad. The Hamiltonian formulation and the constraints are obtained by
using the Dirac-Bergmann algorithm.
PACS numbers: 04.20.Cv, 04.20.Fy,04.65.+
On a possible new R^2 theory of supergravity
We consider a new MacDowell-Mansouri R^2-type of supergravity theory, an
extension of conformal supergravity, based on the superalgebra Osp(1|8).
Invariance under local symmetries with negative Weyl weight is achieved by
imposing chirality-duality and double-duality constraints on curvatures, along
with the usual constraint of vanishing supertorsion. An analysis of the
remaining gauge symmetries shows that those with vanishing Weyl weight are
invariances of the action at the linearized level. For the symmetries with
positive Weyl weight we find that invariance of the action would require
further modifications of the transformation rules. This conclusion is supported
by a kinematical analysis of the closure of the gauge algebra.Comment: 52 pages, Late
One-loop surface tensions of (supersymmetric) kink domain walls from dimensional regularization
We consider domain walls obtained by embedding the 1+1-dimensional
-kink in higher dimensions. We show that a suitably adapted dimensional
regularization method avoids the intricacies found in other regularization
schemes in both supersymmetric and non-supersymmetric theories. This method
allows us to calculate the one-loop quantum mass of kinks and surface tensions
of kink domain walls in a very simple manner, yielding a compact d-dimensional
formula which reproduces many of the previous results in the literature. Among
the new results is the nontrivial one-loop correction to the surface tension of
a 2+1 dimensional N=1 supersymmetric kink domain wall with chiral domain-wall
fermions.Comment: 23 pages, LATeX; v2: 25 pages, 2 references added, extended
discussion of renormalization schemes which dispels apparent contradiction
with previous result
On the Dirac Eigenvalues as Observables of the on-shell N=2 D=4 Euclidean Supergravity
We generalize previous works on the Dirac eigenvalues as dynamical variables
of the Euclidean gravity and N=1 D=4 supergravity to on-shell N=2 D=4 Euclidean
supergravity. The covariant phase space of the theory is defined as as the
space of the solutions of the equations of motion modulo the on-shell gauge
transformations. In this space we define the Poisson brackets and compute their
value for the Dirac eigenvalues.Comment: 10 pages, LATeX fil
Comparing Aimed Movements in the Real World and in Virtual Reality
The study of aimed movements has a long history, starting at least as far back as 1899 when Woodworth proposed a two-component model in which aimed movements are broken into an initial ballistic phase and an additional control phase. In this paper, we use Woodworthâs model for experimentally comparing aimed movements in the real world with those in a virtual environment. Trajectories from real world movements have been collected and compared to trajectories of movements taken from a virtual environment. From this, we show that significant temporal differences arise in both the ballistic and control phases, but the difference is much larger in the control phase; usersâ improvement is relatively greater in the virtual world than in the real world. They progress more in ballistic phase in the real world, but more in correction phase in the virtual world. These results allow us to better understand the pointing tasks in virtual environments
Parity violating spin-two gauge theories
Nonlinear covariant parity-violating deformations of free spin-two gauge
theory are studied in n>2 spacetime dimensions, using a linearized frame and
spin-connection formalism, for a set of massless spin-two fields. It is shown
that the only such deformations yielding field equations with a second order
quasilinear form are the novel algebra-valued types in n=3 and n=5 dimensions
already found in some recent related work concentrating on lowest order
deformations. The complete form of the deformation to all orders in n=5
dimensions is worked out here and some features of the resulting new
algebra-valued spin-two gauge theory are discussed. In particular, the internal
algebra underlying this theory on 5-dimensional Minkowski space is shown to
cause the energy for the spin-two fields to be of indefinite sign. Finally, a
Kaluza-Klein reduction to n=4 dimensions is derived, giving a parity-violating
nonlinear gauge theory of a coupled set of spin-two, spin-one, and spin-zero
massless fields.Comment: 17 page
Comparing Aimed Movements in the Real World and in Virtual Reality
The study of aimed movements has a long history, starting at least as far back as 1899 when Woodworth proposed a two-component model in which aimed movements are broken into an initial ballistic phase and an additional control phase. In this paper, we use Woodworthâs model for experimentally comparing aimed movements in the real world with those in a virtual environment. Trajectories from real world movements have been collected and compared to trajectories of movements taken from a virtual environment. From this, we show that significant temporal differences arise in both the ballistic and control phases, but the difference is much larger in the control phase; usersâ improvement is relatively greater in the virtual world than in the real world. They progress more in ballistic phase in the real world, but more in correction phase in the virtual world. These results allow us to better understand the pointing tasks in virtual environments
Green function Retrieval and Time-reversal in a Disordered World
We apply the theory of multiple wave scattering to two contemporary, related
topics: imaging with diffuse correlations and stability of time-reversal of
diffuse waves, using equipartition, coherent backscattering and frequency
speckles as fundamental concepts.Comment: 1 figur
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