The impact on cosmology of a primordial scaling field

A scalar field with an exponential potential has the particular property that it is attracted into a solution in which its energy scales as the dominant component (radiation or matter) of the Universe, contributing a fixed fraction of the total energy density. We briefly discuss the dynamics of such a scalar field and its impact on Big Bang nucleosynthesis, the growth of large scale structure and abundance of damped Lyman$-\alpha$ systems at high redshift. Given the simplicity of the model, its theoretical motivation, and its success in matching observations, we argue that it should be taken on par with other currently viable models of structure formation.Comment: 3 pages, uses prcrc.sty, 2 figures, to be published in proceedings of Dark Matter '9

Pension Reform in Brazil: Transitional Issues in a Model with Endogenous Labor Supply

Brazilian PAYG system has been under financial stress and needs to be reformed. I use a computational general equilibrium model, with 55 overlapping generations to simulate macroeconomic and welfare impacts of alternative social security reforms. Transition turns out to have quite different redistributional effects for the generations involved depending on which tax is used to finance it. Under a variety of possible transitional schemes, there is no tax path that is strictly preferred by every generation.Social Security, Welfare, General Equilibrium, Macroeconomics, Overlapping Generation

Ricci focusing, shearing, and the expansion rate in an almost homogeneous Universe

The Universe is inhomogeneous, and yet it seems to be incredibly well-characterised by a homogeneous relativistic model. One of the current challenges is to accurately characterise the properties of such a model. In this paper we explore how inhomogeneities may affect the overall optical properties of the Universe by quantifying how they can bias the redshift-distance relation in a number of toy models that mimic the real Universe. The models that we explore are statistically homogeneous on large scales. We find that the effect of inhomogeneities is of order of a few percent, which can be quite important in precise estimation of cosmological parameters. We discuss what lessons can be learned to help us tackle a more realistic inhomogeneous universe.Comment: 22 pages, 8 figure

Skinning the Cat: Education Distribution, Changes in the School Premium and Earnings Inequality

This paper applies the procedure in JUHN ET ALL (1993) to decompose changes in income inequality over time in terms of education-related causal factors: school premiums, educational distribution and residual changes. The main conclusion is that reductions in the school premiums have systematically had a negative impact on income inequality during the last twenty years. At the same time, education has become more unequally distributed for individuals below the median labor income level and more equally distributed for those above it. The combination of the two forces has reduced income dispersion for the top half of earners, and slightly increased it among the bottom half. This difference in trends of educational distribution lies behind an apparently stable profile of income inequality (considering the whole earnings distribution).

Constraining ultra large-scale cosmology with multiple tracers in optical and radio surveys

Multiple tracers of the cosmic density field, with different bias, number and luminosity evolution, can be used to measure the large-scale properties of the Universe. We show how an optimal combination of tracers can be used to detect general-relativistic effects in the observed density of sources. We forecast for the detectability of these effects, as well as measurements of primordial non-Gaussianity and large-scale lensing magnification with current and upcoming large-scale structure experiments. In particular we quantify the significance of these detections in the short term with experiments such as the Dark Energy Survey (DES), and in the long term with the Large Synoptic Survey Telescope (LSST) and the Square Kilometre Array (SKA). We review the main observational challenges that must be overcome to carry out these measurements.Comment: 19 pages, 10 figure

Eddington's theory of gravity and its progeny

We resurrect Eddington's proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times we find that there is a minimum length (and maximum density) at early times, clearly pointing to an alternative theory of the Big Bang. We thus argue that the modern formulation of Eddington's theory, Born-Infeld gravity, presents us with a novel, non-singular description of the Universe.Comment: 4 Pages, 2 Figures, Accepted to PRL (typos corrected