1,684 research outputs found
On Killing vectors in initial value problems for asymptotically flat space-times
The existence of symmetries in asymptotically flat space-times are studied
from the point of view of initial value problems. General necessary and
sufficient (implicit) conditions are given for the existence of Killing vector
fields in the asymptotic characteristic and in the hyperboloidal initial value
problem (both of them are formulated on the conformally compactified space-time
manifold)
Local twistors and the conformal field equations
This note establishes the connection between Friedrich's conformal field
equations and the conformally invariant formalism of local twistors.Comment: LaTeX2e Minor corrections of misprints et
A Scheme to Numerically Evolve Data for the Conformal Einstein Equation
This is the second paper in a series describing a numerical implementation of
the conformal Einstein equation. This paper deals with the technical details of
the numerical code used to perform numerical time evolutions from a "minimal"
set of data.
We outline the numerical construction of a complete set of data for our
equations from a minimal set of data. The second and the fourth order
discretisations, which are used for the construction of the complete data set
and for the numerical integration of the time evolution equations, are
described and their efficiencies are compared. By using the fourth order scheme
we reduce our computer resource requirements --- with respect to memory as well
as computation time --- by at least two orders of magnitude as compared to the
second order scheme.Comment: 20 pages, 12 figure
General Relativistic Scalar Field Models in the Large
For a class of scalar fields including the massless Klein-Gordon field the
general relativistic hyperboloidal initial value problems are equivalent in a
certain sense. By using this equivalence and conformal techniques it is proven
that the hyperboloidal initial value problem for those scalar fields has an
unique solution which is weakly asymptotically flat. For data sufficiently
close to data for flat spacetime there exist a smooth future null infinity and
a regular future timelike infinity.Comment: 22 pages, latex, AGG 1
A Method for Calculating the Structure of (Singular) Spacetimes in the Large
A formalism and its numerical implementation is presented which allows to
calculate quantities determining the spacetime structure in the large directly.
This is achieved by conformal techniques by which future null infinity
(\Scri{}^+) and future timelike infinity () are mapped to grid points on
the numerical grid. The determination of the causal structure of singularities,
the localization of event horizons, the extraction of radiation, and the
avoidance of unphysical reflections at the outer boundary of the grid, are
demonstrated with calculations of spherically symmetric models with a scalar
field as matter and radiation model.Comment: 29 pages, AGG2
Measurement of heavy-hole spin dephasing in (InGa)As quantum dots
We measure the spin dephasing of holes localized in self-assembled (InGa)As
quantum dots by spin noise spectroscopy. The localized holes show a distinct
hyperfine interaction with the nuclear spin bath despite the p-type symmetry of
the valence band states. The experiments reveal a short spin relaxation time
{\tau}_{fast}^{hh} of 27 ns and a second, long spin relaxation time
{\tau}_{slow}^{hh} which exceeds the latter by more than one order of
magnitude. The two times are attributed to heavy hole spins aligned
perpendicular and parallel to the stochastic nuclear magnetic field. Intensity
dependent measurements and numerical simulations reveal that the long
relaxation time is still obscured by light absorption, despite low laser
intensity and large detuning. Off-resonant light absorption causes a
suppression of the spin noise signal due to the creation of a second hole
entailing a vanishing hole spin polarization.Comment: accepted to be published in AP
Numerical treatment of the hyperboloidal initial value problem for the vacuum Einstein equations. III. On the determination of radiation
We discuss the issue of radiation extraction in asymptotically flat
space-times within the framework of conformal methods for numerical relativity.
Our aim is to show that there exists a well defined and accurate extraction
procedure which mimics the physical measurement process. It operates entirely
intrisically within \scri^+ so that there is no further approximation
necessary apart from the basic assumption that the arena be an asymptotically
flat space-time. We define the notion of a detector at infinity by idealising
local observers in Minkowski space. A detailed discussion is presented for
Maxwell fields and the generalisation to linearised and full gravity is
performed by way of the similar structure of the asymptotic fields.Comment: LaTeX2e,13 pages,2 figure
Fidelity for Multimode Thermal Squeezed States
In the theory of quantum transmission of information the concept of fidelity
plays a fundamental role. An important class of channels, which can be
experimentally realized in quantum optics, is that of Gaussian quantum
channels. In this work we present a general formula for fidelity in the case of
two arbitrary Gaussian states. From this formula one can get a previous result
(H. Scutaru, J. Phys. A: Mat. Gen {\bf 31}, 3659 (1998)), for the case of a
single mode; or, one can apply it to obtain a closed compact expression for
multimode thermal states.Comment: 5 pages, RevTex, submitted to Phys. Rev.
Theory for Spin-Polarized Oscillations in Nonlinear Magneto-Optics due to Quantum Well States
Using an electronic tight-binding theory we calculate the nonlinear
magneto-optical response from an x-Cu/1Fe/Cu(001) film as a function of
frequency and Cu overlayer thickness (x=3 ... 25). We find very strong
spin-polarized quantum well oscillations in the nonlinear magneto-optical Kerr
effect (NOLIMOKE). These are enhanced by the large density of Fe states
close to the Fermi level acting as intermediate states for frequency doubling.
In good agreement with experiment we find two oscillation periods of 6-7 and 11
monolayers the latter being more pronounced.Comment: 12 pages, Revtex, 3 postscript figure
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