2,591 research outputs found
Non-Gaussian statistics, maxwellian derivation and stellar polytropes
In this letter we discuss the Non-gaussian statistics considering two
aspects. In the first, we show that the Maxwell's first derivation of the
stationary distribution function for a dilute gas can be extended in the
context of Kaniadakis statistics. The second one, by investigating the stellar
system, we study the Kaniadakis analytical relation between the entropic
parameter and stellar polytrope index . We compare also the
Kaniadakis relation with proposed in the Tsallis
framework.Comment: 10 pages, 1 figur
The electromagnetic coupling and the dark side of the Universe
We examine the properties of dark energy and dark matter through the study of
the variation of the electromagnetic coupling. For concreteness, we consider
the unification model of dark energy and dark matter, the generalized Chaplygin
gas model (GCG), characterized by the equation of state
, where is the pressure, is the energy
density and and are positive constants. The coupling of
electromagnetism with the GCG's scalar field can give rise to such a variation.
We compare our results with experimental data, and find that the degeneracy on
parameters and , , is
considerable.Comment: Revtex 4, 5 pages and 5 figure
String Theory and Cosmology
We discuss the main cosmological implications of considering string-loop
effects and a potential for the dilaton in the lowest order string effective
action. Our framework is based on the effective model arising from regarding
homogeneous and isotropic dilaton, metric and Yang-Mills field configurations.
The issues of inflation, entropy crisis and the Polonyi problem as well as the
problem of the cosmological constant are discussed.Comment: 7 pages, plain Tex, no figure
Generalized nonuniform dichotomies and local stable manifolds
We establish the existence of local stable manifolds for semiflows generated
by nonlinear perturbations of nonautonomous ordinary linear differential
equations in Banach spaces, assuming the existence of a general type of
nonuniform dichotomy for the evolution operator that contains the nonuniform
exponential and polynomial dichotomies as a very particular case. The family of
dichotomies considered allow situations for which the classical Lyapunov
exponents are zero. Additionally, we give new examples of application of our
stable manifold theorem and study the behavior of the dynamics under
perturbations.Comment: 18 pages. New version with minor corrections and an additional
theorem and an additional exampl
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