17,678 research outputs found
Large-angle non-Gaussianity in simulated high-resolution CMB maps
A detection or nondetection of primordial non-Gaussianity by using the cosmic
microwave background radiation (CMB) offers a way of discriminating
inflationary scenarios and testing alternative models of the early universe.
This has motivated the considerable effort that has recently gone into the
study of theoretical features of primordial non-Gaussianity and its detection
in CMB data. Among such attempts to detect non-Gaussianity, there is a
procedure that is based upon two indicators constructed from the skewness and
kurtosis of large-angle patches of CMB maps, which have been proposed and used
to study deviation from Gaussianity in the WMAP data. Simulated CMB maps
equipped with realistic primordial non-Gaussianity are essential tools to test
the viability of non-Gaussian indicators in practice, and also to understand
the effect of systematics, foregrounds and other contaminants. In this work we
extend and complement the results of our previous works by performing an
analysis of non-Gaussianity of the high-angular resolution simulated CMB
temperature maps endowed with non-Gaussianity of the local type, for which the
level of non-Gaussianity is characterized by the dimensionless parameter
Comment: 8 pages, 3 figure
Classification of Energy Momentum Tensors in Dimensional Space-times: a Review
Recent developments in string theory suggest that there might exist extra
spatial dimensions, which are not small nor compact. The framework of a great
number of brane cosmological models is that in which the matter fields are
confined on a brane-world embedded in five dimensions (the bulk). Motivated by
this we review the main results on the algebraic classification of second order
symmetric tensors in 5-dimensional space-times. All possible Segre types for a
symmetric two-tensor are found, and a set of canonical forms for each Segre
type is obtained. A limiting diagram for the Segre types of these symmetric
tensors in 5-D is built. Two theorems which collect together some basic results
on the algebraic structure of second order symmetric tensors in 5-D are
presented. We also show how one can obtain, by induction, the classification
and the canonical forms of a symmetric two-tensor on n-dimensional (n > 5)
spaces from its classification in 5-D spaces, present the Segre types in n-D
and the corresponding canonical forms. This classification of symmetric
two-tensors in any n-D spaces and their canonical forms are important in the
context of n-dimensional brane-worlds context and also in the framework of 11-D
supergravity and 10-D superstrings.Comment: LaTex2e, 18 pages. To appear in Braz.J.Phys (2004
Fold-Saddle Bifurcation in Non-Smooth Vector Fields on the Plane
This paper presents results concerning bifurcations of 2D piecewise-smooth
dynamical systems governed by vector fields. Generic three parameter families
of a class of Non-Smooth Vector Fields are studied and its bifurcation diagrams
are exhibited. Our main result describes the unfolding of the so called
Fold-Saddle singularity
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