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

Brane Cosmology from Heterotic String Theory

We consider brane cosmologies within the context of five-dimensional actions with O(a') higher curvature corrections. The actions are compatible with bulk string amplitude calculations from heterotic string theory. We find wrapped solutions that satisfy the field equations in an approximate but acceptable manner given their complexity, where the internal four-dimensional scale factor is naturally inflating, having an exponential De-Sitter form. The temporal dependence of the metric components is non-trivial so that this metric cannot be factored as in a conformally flat case. The effective Planck mass is finite and the brane solutions localize four-dimensional gravity, while the four-dimensional gravitational constant varies with time. The Hubble constant can be freely specified through the initial value of the scalar field, to conform with recent data.Comment: 15 pages, 3 figures, LaTeX, Accepted for Publication in IJT

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

Electroweak Baryogenesis in the Presence of an Isosinglet Quark

We consider the possibility of electroweak baryogenesis in a simple extension of the standard model with an extra singlet complex scalar and a vector-like down quark. We show that in the present model the first-order electroweak phase transition can be strong enough to avoid the baryon asymmetry washout by sphalerons and that the CP-violating effects can be sufficient to explain the observed baryon-to-entropy ratio nB/s ~ 10^(-10). Other appealing features of the model include the generation of a CKM phase from spontaneous CP breaking at a high energy scale and a possible solution of the strong CP problem through the natural suppression of the parameter theta.Comment: LaTeX, 19 pages, 2 EPS figures, uses epsf, amsmath, amsfonts, amssym

Supergravity Inflation on the Brane

We study N=1 Supergravity inflation in the context of the braneworld scenario. Particular attention is paid to the problem of the onset of inflation at sub-Planckian field values and the ensued inflationary observables. We find that the so-called $\eta$-problem encountered in supergravity inspired inflationary models can be solved in the context of the braneworld scenario, for some range of the parameters involved. Furthermore, we obtain an upper bound on the scale of the fifth dimension, M_5 \lsim 10^{-3} M_P, in case the inflationary potential is quadratic in the inflaton field, $\phi$. If the inflationary potential is cubic in $\phi$, consistency with observational data requires that $M_5 \simeq 9.2 \times 10^{-4} M_P$.Comment: 6 pages, 1 figure, to appear in Phys. Rev.

Role of Modified Chaplygin Gas as a Dark Energy Model in Collapsing Spherically Symmetric Cloud

In this work, gravitational collapse of a spherical cloud, consists of both dark matter and dark energy in the form of modified Chaplygin gas is studied. It is found that dark energy alone in the form of modified Chaplygin gas forms black hole. Also when both components of the fluid are present then the collapse favors the formation of black hole in cases the dark energy dominates over dark matter. The conclusion is totally opposite to the usually known results.Comment: 7 Latex Pages, RexTex style, No figure

Halo Properties in Cosmological Simulations of Self-Interacting Cold Dark Matter

We present a comparison of halo properties in cosmological simulations of collisionless cold dark matter (CDM) and self-interacting dark matter (SIDM) for a range of dark matter cross sections. We find, in agreement with various authors, that CDM yields cuspy halos that are too centrally concentrated as compared to observations. Conversely, SIDM simulations using a Monte Carlo N-body technique produce halos with significantly reduced central densities and flatter cores with increasing cross section. We introduce a concentration parameter based on enclosed mass that we expect will be straightforward to determine observationally, unlike that of Navarro, Frenk & White, and provide predictions for SIDM and CDM. SIDM also produces more spherical halos than CDM, providing possibly the strongest observational test of SIDM. We discuss our findings in relation to various relevant observations as well as SIDM simulations of other groups. Taking proper account of simulation limitations, we find that a dark matter cross section per unit mass of sigma_DM ~= 10^{-23}-10^{-24} cm^2/GeV is consistent with all current observational constraints.Comment: 14 pages, submitted to Ap

Instabilities in neutrino-plasma density waves

One examines the interaction and possible resonances between supernova neutrinos and electron plasma waves. The neutrino phase space distribution and its boundary regions are analyzed in detail. It is shown that the boundary regions are too wide to produce non-linear resonant effects. The growth or damping rates induced by neutrinos are always proportional to the neutrino flux and $G_{{\rm F}}^{2}$.Comment: 9 pages, a few words modified to match PRD publicatio

Necrotizing Fasciitis and Middle Ear Infection

A fasceíte necrosante (FN) é uma doença rara em pediatria. Na maior parte dos casos surge como complicação de varicela, sendo a pele habitualmente a porta de entrada e o Streptococcus pyogenes o agente mais frequente. Os autores descrevem um caso clínico de uma criança de 8 anos, previamente saudável que, no contexto de uma otite média aguda medicada com um anti-inflamatório não esteróide (AINE), desenvolve uma infecção invasiva a Streptococcus 13 hemoliticus do grupo A