3,510,790 research outputs found
Weak Field Expansion of Gravity: Graphs, Matrices and Topology
We present some approaches to the perturbative analysis of the classical and
quantum gravity. First we introduce a graphical representation for a global
SO(n) tensor (\pl)^d h_\ab, which generally appears in the weak field
expansion around the flat space: g_\mn=\del_\mn+h_\mn. Making use of this
representation, we explain 1) Generating function of graphs (Feynman diagram
approach), 2) Adjacency matrix (Matrix approach), 3) Graphical classification
in terms of "topology indices" (Topology approach), 4) The Young tableau
(Symmetric group approach). We systematically construct the global SO(n)
invariants. How to show the independence and completeness of those invariants
is the main theme. We explain it taking simple examples of \pl\pl h-, {and}
(\pl\pl h)^2- invariants in the text. The results are applied to the analysis
of the independence of general invariants and (the leading order of) the Weyl
anomalies of scalar-gravity theories in "diverse" dimensions (2,4,6,8,10
dimensions).Comment: 41pages, 26 figures, Latex, epsf.st
Semi-Invariant Terms for Gauged Non-Linear Sigma-Models
We determine all the terms that are gauge-invariant up to a total spacetime
derivative ("semi-invariant terms") for gauged non-linear sigma models.
Assuming that the isotropy subgroup of the gauge group is compact or
semi-simple, we show that (non-trivial) such terms exist only in odd dimensions
and are equivalent to the familiar Chern-Simons terms for the subgroup .
Various applications are mentioned, including one to the gauging of the
Wess-Zumino-Witten terms in even spacetime dimensions. Our approach is based on
the analysis of the descent equation associated with semi-invariant terms.Comment: section 6 expande
Cosmokinetics: A joint analysis of Standard Candles, Rulers and Cosmic Clocks
We study the accelerated expansion of the universe by using the kinematic
approach. In this context, we parameterize the deceleration parameter, q(z), in
a model independent way. Assuming three simple parameterizations we reconstruct
q(z). We do the joint analysis with combination of latest cosmological data
consisting of standard candles (Supernovae Union2 sample), standard ruler
(CMB/BAO), cosmic clocks (age of passively evolving galaxies) and Hubble (H(z))
data. Our results support the accelerated expansion of the universe.Comment: PDFLatex, 15 pages, 12 pdf figures, revised version to appear in JCA
Exact asymptotic behavior of magnetic stripe domain arrays
The classical problem of magnetic stripe domain behavior in films and plates
with uniaxial magnetic anisotropy is treated. Exact analytical results are
derived for the stripe domain widths as function of applied perpendicular
field, , in the regime where the domain period becomes large. The stripe
period diverges as , where is the critical (infinite
period) field, an exact result confirming a previous conjecture. The
magnetization approaches saturation as , a behavior which
compares excellently with experimental data obtained for a m thick
ferrite garnet film. The exact analytical solution provides a new basis for
precise characterization of uniaxial magnetic films and plates, illustrated by
a simple way to measure the domain wall energy. The mathematical approach is
applicable for similar analysis of a wide class of systems with competing
interactions where a stripe domain phase is formed.Comment: 4 pages, 4 figure
Gain-scheduled H∞ control via parameter-dependent Lyapunov functions
Synthesising a gain-scheduled output feedback H∞ controller via parameter-dependent Lyapunov functions for linear parameter-varying (LPV) plant models involves solving an infinite number of linear matrix inequalities (LMIs). In practice, for affine LPV models, a finite number of LMIs can be achieved using convexifying techniques. This paper proposes an alternative approach to achieve a finite number of LMIs. By simple manipulations on the bounded real lemma inequality, a symmetric matrix polytope inequality can be formed. Hence, the LMIs need only to be evaluated at all vertices of such a symmetric matrix polytope. In addition, a construction technique of the intermediate controller variables is also proposed as an affine matrix-valued function in the polytopic coordinates of the scheduled parameters. Computational results on a numerical example using the approach were compared with those from a multi-convexity approach in order to demonstrate the impacts of the approach on parameter-dependent Lyapunov-based stability and performance analysis. Furthermore, numerical simulation results show the effectiveness of these proposed techniques
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