Late time cosmic acceleration from vacuum Brans-Dicke theory in 5D

We show that the scalar-vacuum Brans-Dicke equations in 5D are equivalent to Brans-Dicke theory in 4D with a self interacting potential and an effective matter field. The cosmological implication, in the context of FRW models, is that the observed accelerated expansion of the universe comes naturally from the condition that the scalar field is not a ghost, i.e., $\omega > - 3/2$. We find an effective matter-dominated 4D universe which shows accelerated expansion if $- 3/2 < \omega < - 1$. We study the question of whether accelerated expansion can be made compatible with large values of $\omega$, within the framework of a 5D scalar-vacuum Brans-Dicke theory with variable, instead of constant, parameter $\omega$. In this framework, and based on a general class of solutions of the field equations, we demonstrate that accelerated expansion is incompatible with large values of $\omega$.Comment: In V2 the summary section is expanded. To be published in Classical and Quantum Gravity

Métodos de análise de dados longitudinais para o melhoramento genético da pinha.

O objetivo deste trabalho foi comparar formas de análise de medidas repetidas para o melhoramento da produção de frutos de pinha (Annona squamosa). Vinte progênies de meias?irmãs foram avaliadas por três anos (2003, 2004 e 2005) em delineamento de blocos ao acaso, com cinco repetições, com cada parcela constituída de quatro plantas. A característica avaliada foi o número de frutos por indivíduo. Os modelos de simetria composta, de simetria composta com variâncias heterogêneas, autorregressivo com variâncias heterogêneas, e antedependência estruturada, foram analisados com o programa ASReml. A estimação dos componentes de variância e a predição dos valores genéticos foram feitas com o procedimento REML/BLUP. A comparação dos modelos foi realizada pelo teste de razão de verossimilhança e pelo critério de Akaike. O modelo antedependência estruturada, para os fatores progênie e parcela, e o modelo multivariado, para o fator resíduo, são as melhores abordagens para a análise dos dados, pois propiciam eficiência e parcimônia em relação ao modelo multivariado completo. Com o modelo antedependência estruturada, é possível a identificação de famílias superiores, em cada colheita, e também de famílias com maior número total de frutos

Towards a Precision Cosmology from Starburst Galaxies at z>2

This work investigates the use of a well-known empirical correlation between the velocity dispersion, metallicity, and luminosity in H beta of nearby HII galaxies to measure the distances to HII-like starburst galaxies at high redshifts. This correlation is applied to a sample of 15 starburst galaxies with redshifts between z=2.17 and z=3.39 to constrain Omega_m, using data available from the literature. A best-fit value of Omega_m = 0.21 +0.30 -0.12 in a Lambda-dominated universe and of Omega_m = 0.11 +0.37 -0.19 in an open universe is obtained. A detailed analysis of systematic errors, their causes, and their effects on the values derived for the distance moduli and Omega_m is carried out. A discussion of how future work will improve constraints on Omega_m by reducing the errors is also presented.Comment: 7 pages, 3 figures, accepted for publication in MNRA

The orbit structure of Dynkin curves

Let G be a simple algebraic group over an algebraically closed field k; assume that Char k is zero or good for G. Let \cB be the variety of Borel subgroups of G and let e in Lie G be nilpotent. There is a natural action of the centralizer C_G(e) of e in G on the Springer fibre \cB_e = {B' in \cB | e in Lie B'} associated to e. In this paper we consider the case, where e lies in the subregular nilpotent orbit; in this case \cB_e is a Dynkin curve. We give a complete description of the C_G(e)-orbits in \cB_e. In particular, we classify the irreducible components of \cB_e on which C_G(e) acts with finitely many orbits. In an application we obtain a classification of all subregular orbital varieties admitting a finite number of B-orbits for B a fixed Borel subgroup of G.Comment: 12 pages, to appear in Math

Transition from decelerated to accelerated cosmic expansion in braneworld universes

Braneworld theory provides a natural setting to treat, at a classical level, the cosmological effects of vacuum energy. Non-static extra dimensions can generally lead to a variable vacuum energy, which in turn may explain the present accelerated cosmic expansion. We concentrate our attention in models where the vacuum energy decreases as an inverse power law of the scale factor. These models agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameter. The redshift at which the vacuum energy can start to dominate depends on the mass density of ordinary matter. For Omega = 0.3, the transition from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/- 0.20, which is compatible with SNe data. We set a lower bound on the deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for Omega = 0.3. The future evolution of the universe crucially depends on the time when vacuum starts to dominate over ordinary matter. If it dominates only recently, at an epoch z < 0.64, then the universe is accelerating today and will continue that way forever. If vacuum dominates earlier, at z > 0.64, then the deceleration comes back and the universe recollapses at some point in the distant future. In the first case, quintessence and Cardassian expansion can be formally interpreted as the low energy limit of our model, although they are entirely different in philosophy. In the second case there is no correspondence between these models and ours.Comment: In V2 typos are corrected and one reference is added for section 1. To appear in General Relativity and Gravitatio

Phase Space Analysis of Quintessence Cosmologies with a Double Exponential Potential

We use phase space methods to investigate closed, flat, and open Friedmann-Robertson-Walker cosmologies with a scalar potential given by the sum of two exponential terms. The form of the potential is motivated by the dimensional reduction of M-theory with non-trivial four-form flux on a maximally symmetric internal space. To describe the asymptotic features of run-away solutions we introduce the concept of a `quasi fixed point.' We give the complete classification of solutions according to their late-time behavior (accelerating, decelerating, crunch) and the number of periods of accelerated expansion.Comment: 46 pages, 5 figures; v2: minor changes, references added; v3: title changed, refined classification of solutions, 3 references added, version which appeared in JCA

Quintom dark energy in DGP braneworld cosmology

In this paper we consider a $Z_2$ symmetrical 3-brane embedded in a 5-dimensional spacetime. We study the effective Einstein equation and acceleration condition in presence of the quintom dark energy fluid as the bulk matter field. It is shown that the time-dependent bulk quintom field induces a time-dependent cosmological constant on the brane. In the framework of the DGP model, the effective Einstein equation is obtained in two different cases: i) where the quintom field is considered as the bulk matter field and the brane is empty and, ii) where the quintom dark energy is confined on the brane and the bulk is empty. We show that in both cases one could obtain a self-inflationary solution at late time in positive branch $\epsilon=1$, and an asymptotically static universe in negative branch $\epsilon=-1$.Comment: 12 pages, 8 figure

Restframe I-band Hubble diagram for type Ia supernovae up to redshift z ~0.5

We present a novel technique for fitting restframe I-band light curves on a data set of 42 Type Ia supernovae (SNe Ia). Using the result of the fit, we construct a Hubble diagram with 26 SNe from the subset at 0.01< z<0.1. Adding two SNe at z~0.5 yields results consistent with a flat Lambda-dominated``concordance universe'' ($\Omega_M,\Omega_\Lambda$)=(0.25,0.75). For one of these, SN 2000fr, new near infrared data are presented. The high redshift supernova NIR data are also used to test for systematic effects in the use of SNe Ia as distance estimators. A flat, Lambda=0, universe where the faintness of supernovae at z~0.5 is due to grey dust homogeneously distributed in the intergalactic medium is disfavoured based on the high-z Hubble diagram using this small data-set. However, the uncertainties are large and no firm conclusion may be drawn. We explore the possibility of setting limits on intergalactic dust based on B-I and B-V colour measurements, and conclude that about 20 well measured SNe are needed to give statistically significant results. We also show that the high redshift restframe I-band data points are better fit by light curve templates that show a prominent second peak, suggesting that they are not intrinsically underluminous.Comment: Accepted for publication in A&A (01/04/2005

The Influence of Free Quintessence on Gravitational Frequency Shift and Deflection of Light with 4D momentum

Based on the 4D momentum, the influence of quintessence on the gravitational frequency shift and the deflection of light are examined in modified Schwarzschild space. We find that the frequency of photon depends on the state parameter of quintessence $w_q$: the frequency increases for $-1<w_q<-1/3$ and decreases for $-1/3<w_q<0$. Meanwhile, we adopt an integral power number $a$ ($a = 3\omega_q + 2$) to solve the orbital equation of photon. The photon's potentials become higher with the decrease of $\omega_q$. The behavior of bending light depends on the state parameter $\omega_q$ sensitively. In particular, for the case of $\omega_q = -1$, there is no influence on the deflection of light by quintessence. Else, according to the H-masers of GP-A redshift experiment and the long-baseline interferometry, the constraints on the quintessence field in Solar system are presented here.Comment: 12 pages, 2 figures, 4 tables. European Physical Journal C in pres

Cosmology With Non-Minimally Coupled K-Field

We consider non-minimally coupled (with gravity) scalar field with non-canonical kinetic energy. The form of the kinetic term is of Dirac-Born-Infeld (DBI) form.We study the early evolution of the universe when it is sourced only by the k-field, as well as late time evolution when both the matter and k-field are present. For the k-field, we have considered constant potential as well as potential inspired from Boundary String Field Theory (B-SFT). We show that it is possible to have inflationary solution in early time as well as late time accelerating phase. The solutions also exhibit attractor property in a sense that it does not depend on the initial conditions for a certain values of the parameters.Comment: 10 pages, Revtex style, 14 eps figures, to appear in General Relativity and Gravitatio