Exact solutions of Brans-Dicke cosmology with decaying vacuum density

We investigate cosmological solutions of Brans-Dicke theory with both the vacuum energy density and the gravitational constant decaying linearly with the Hubble parameter. A particular class of them, with constant deceleration factor, sheds light on the cosmological constant problems, leading to a presently small vacuum term, and to a constant ratio between the vacuum and matter energy densities. By fixing the only free parameter of these solutions, we obtain cosmological parameters in accordance with observations of both the relative matter density and the universe age. In addition, we have three other solutions, with Brans-Dicke parameter w = -1 and negative cosmological term, two of them with a future singularity of big-rip type. Although interesting from the theoretical point of view, two of them are not in agreement with the observed universe. The third one leads, in the limit of large times, to a constant relative matter density, being also a possible solution to the cosmic coincidence problem.Comment: Minor changes, references added. Version accepted for publication in Classical and Quantum Gravit

Exact solutions of Brans-Dicke cosmology and the cosmic coincidence problem

We present some cosmological solutions of Brans-Dicke theory, characterized by a decaying vacuum energy density and by a constant relative matter density. With these features, they shed light on the cosmological constant problems, leading to a presently small vacuum term, and to a constant ratio between the vacuum and matter energy densities. By fixing the only free parameter of our solutions, we obtain cosmological parameters in accordance with observations of the relative matter density, the universe age and redshift-distance relations.Comment: To appear in Brazilian Journal of Physics (proceedings of the conference 100 Years of Relativity, Sao Paulo, August 2005

Who benefits from labor market regulations? Chile 1960-1998

Economists have examined the impact of labor market regulations on the level of employment. But there are many reasons to suspect that the impact of regulations differs across types of workers. In this paper the authors take advantage of the unusually large variance in labor policy in Chile to examine how different labor market regulations affect the distribution of employment and the employment rates across age, gender, and skill levels. To this effect, they use a sample of repeated cross-section household surveys spanning the period 1960-98 and measures of the evolution of job security provisions and minimum wages across time. The results suggest large distribution effects. The authors find that employment security provisions and minimum wages reduce the share of youth and unskilled employment as well as their employment rates. They also find large effects on the distribution of employment between women and men.Labor Policies,Labor Management and Relations,Environmental Economics&Policies,Public Health Promotion,Health Monitoring&Evaluation,Environmental Economics&Policies,Health Monitoring&Evaluation,Labor Management and Relations,Labor Standards,Youth and Governance

Aggregate agricultural supply response in developing countries : a survey of selected issues

The authors review several studies of the aggregate agricultural supply response. Using both economic and econometric reasons, they argue that time series estimation typically generates a downward-biased estimate of the response to a credible reform. Even though time series estimates can provide an accurate picture of past behavoiral relations, they do not provide an adequate basis for forecasting the impact of policy reform. This is especially true in developing countries, where policy reforms involve large changes and have included agricultural price reform, industrial trade liberalization, financial sector reform, and macroeconomic stabilization. Under those circumstances, parameters values obtained under the former policy regime have little relevance in the new regime. The authors also argue that investment in public goods should be viewed as complementary to, not competitive with, price policy. They claim that to select the policy with the biggest impact on output makes no sense. They provide what they consider to be better criteria for choosing the best from alternative policies.Environmental Economics&Policies,Payment Systems&Infrastructure,Economic Theory&Research,Markets and Market Access,Labor Policies,Economic Theory&Research,Environmental Economics&Policies,Access to Markets,Markets and Market Access,Inequality

What determines the quality of institutions?

In trying to explain institutional quality, different authors have come to conflicting conclusions. In tackling the problem themselves, the authors show three things. First, openness is positively and pretty robustly associated with institutional quality. To minimize selection bias, the authors use data sets with the greatest cross-country coverage, though they also test the significance of the variables for smaller sample sizes. The results confirm that both natural and policy measures of openness are important. Concentration of trade in natural resource exports continues to be associated with poor institutional quality after openness in trade is accounted for. Second,"social"variables, such as income inequality or ethnic diversity, are not associated with institutional quality. The significance of the inequality variable disappears when continent dummy variables are included for Africa and Latin America. Third, features of specific institutions, such as freedom of the press and checks and balances in the political system, are positively associated with overall perceptions of institutional quality. These findings hold strongly across different data sets and samples even after the authors control for the variables commonly used in the literature.Decentralization,Environmental Economics&Policies,Public Institution Analysis&Assessment,Economic Theory&Research,Poverty Monitoring&Analysis,Governance Indicators,Economic Policy, Institutions and Governance,Public Institution Analysis&Assessment,Economic Theory&Research,Poverty Monitoring&Analysis

Probing the Radio Loud/Quiet AGN dichotomy with quasar clustering

We investigate the clustering properties of 45441 radio-quiet quasars (RQQs) and 3493 radio-loud quasars (RLQs) drawn from a joint use of the Sloan Digital Sky Survey (SDSS) and Faint Images of the Radio Sky at 20 cm (FIRST) surveys in the range $0.3<z<2.3$. This large spectroscopic quasar sample allow us to investigate the clustering signal dependence on radio-loudness and black hole (BH) virial mass. We find that RLQs are clustered more strongly than RQQs in all the redshift bins considered. We find a real-space correlation length of $r_{0}=6.59_{-0.24}^{+0.33}\,h^{-1}\,\textrm{Mpc}$ and $r_{0}=10.95_{-1.58}^{+1.22}\,h^{-1}\,\textrm{Mpc}$ {\normalsize{}for} RQQs and RLQs, respectively, for the full redshift range. This implies that RLQs are found in more massive host haloes than RQQs in our samples, with mean host halo masses of $\sim4.9\times10^{13}\,h^{-1}\,M_{\odot}$ and $\sim1.9\times10^{12}\,h^{-1}\,M_{\odot}$, respectively. Comparison with clustering studies of different radio source samples indicates that this mass scale of $\gtrsim1\times10^{13}\,h^{-1}\,M_{\odot}$ is characteristic for the bright radio-population, which corresponds to the typical mass of galaxy groups and galaxy clusters. The similarity we find in correlation lengths and host halo masses for RLQs, radio galaxies and flat-spectrum radio quasars agrees with orientation-driven unification models. Additionally, the clustering signal shows a dependence on black hole (BH) mass, with the quasars powered by the most massive BHs clustering more strongly than quasars having less massive BHs. We suggest that the current virial BH mass estimates may be a valid BH proxies for studying quasar clustering. We compare our results to a previous theoretical model that assumes that quasar activityComment: 15 pages, 13 figures, A&A in pres

Time Series Analysis of Export Demand Equations: A Cross-Country Analysis

The paper estimates export demand elasticities for a large number of developing and industrial countries, using time-series techniques that account for the nonstationarity in the data. The average long-run price and income elasticities are found to be approximately -1 and 1.5, respectively. Thus, exports do react to both the trade partners' income and to relative prices. Africa faces the lowest income elasticities for its exports, while Asia has both the highest income and price elasticities. The price and income elasticity estimates have good statistical properties. Copyright 1999, International Monetary Fund