Breaking the cosmological background degeneracy by two-fluid perturbations in f(R) gravity

One of the exact solutions of f(R) theories of gravity in the presence of different forms of matter exactly mimics the LCDM solution of general relativity at the background level. In this work we study the evolution of scalar cosmological perturbations in the covariant and gauge-invariant formalism and show that although the background in such a model is indistinguishable from the standard LCDM cosmology, this degeneracy is broken at the level of first-order perturbations. This is done by predicting different rates of structure formation in LCDM and the f(R) model both in the complete and quasi\hs static regimes.Comment: 17 pages, 19 figure

Working Paper 120 - Community Based Health Insurance Schemes in Africa: The Case of Rwanda

Community-based health insurance schemes (Mutuelles) in Rwanda are one of the largest experiments in community based risk-sharing mechanisms in Sub-Saharan Africa for health related problems. This study examines the impact of the program on demand for modern health care, mitigation of out-of-pocket catastrophic health expenditure and social inclusiveness based on a nationally representative household survey using traditional regression approach and matching estimator popular in the evaluation literature. Our findings suggest that Mutuelles have been successful in increasing utilization of modern health care services and reducing catastrophic health related expenditure. According to our preferred method, higher utilization of health care services was found among the insured non-poor than insured poor households, with comparable effect in reducing health-related expenditure shocks.

Working Paper 121 - Financing Goal 1 of the MDGs in Africa: Some Evidence from Cross-Country Data

This study explores the role of development assistance to finance the required growth to reduce extreme poverty by half in 2015 in Africa. The study utilizes the financing gap and “optimal” aid allocation models to explore the implications of efficient aid utilization and global-aid allocation on total aid required to meet goal 1 of the MDGs. The findings suggest that efficiency in the utilization of development assistance by recipients, or optimal disbursement of aid by donors would take the Africa region a long way in reaching the target without additional assistance. This evidence provides empirical support to the recent debate on aid-effectiveness in particular and reforming aid architecture in general.

Working Paper 122 - Welfare Analysis Using Data from the International Comparison Program for Africa

This paper uses data from the International Comparison Program 2005 to recover income and price elasticity estimates for the African continent using the Extended Linear Expenditure System for 13 broadly defined commodities. The results can be used for aggregate welfare comparison in such global models as GTAP (Global Trade Analysis Project) and exercises to infer welfare impact of relative price shocks at the continental level. In a heuristic way also, it is possible to derive a “utility-consistent” global poverty line from the demand function that could be compared with the popular international poverty lines. Results generally indicate that changes in the price of food items could lead to greater welfare loss compared to changes in the price of energy or other commodities. Income elasticity estimates generally fell within bounds usually found from household surveys. At the continental level, the estimated utility-consistent subsistence expenditure is close to 1.12 dollar a day per person, which is quite close to the 1.08 dollar a day global (international) poverty line used in 2005 to measure absolute poverty.

Private Trees as Household Assets and Determinants of Tree-Growing Behavior in Rural Ethiopia

This study looked into tree-growing behavior of rural households in Ethiopia. With data collected at household and parcel levels from the four major regions of Ethiopia, we analyzed the decision to grow trees and the number of trees grown, using such econometric strategies as a zero-inflated negative binomial model, Heckman’s two-step procedure, and panel data techniques. Our findings show the importance of analysis at the parcel level in addition to the more common household-level. Moreover, the empirical analysis indicates that the determinants of the decision to grow trees are not necessarily the same as those involved in deciding the number of trees grown. Land certification, as an indicator of tenure security, increases the likelihood that households will grow trees, but is not a significant determinant of the number of trees grown. Other variables, such as risk aversion, land size, adult male labor, and education of household head, also influence the number of trees grown. In general, the results suggest the need to use education and/or awareness of the role and importance of trees and point out the importance of household endowments and behavior, such as land, labor, and risk aversion, for tree growing. Finally, we observed that, while tree planting is practiced in all four regions covered, there are variations across regions.trees as assets, tree growing, Ethiopia

Shear-free Anisotropic Cosmological Models in f(R) Gravity

We study a class of shear-free, homogeneous but anisotropic cosmological models with imperfect matter sources in the context of f(R) gravity. We show that the anisotropic stresses are related to the electric part of the Weyl tensor in such a way that they balance each other. We also show that within the class of orthogonal f(R) models, small perturbations of shear are damped, and that the electric part of the Weyl tensor and the anisotropic stress tensor decay with the expansion as well as the heat flux of the curvature fluid. Specializing in locally rotationally symmetric spacetimes in orthonormal frames, we examine the late-time behaviour of the de Sitter universe in $f(R)$ gravity. For the Starobinsky model of f(R), we study the evolutionary behavior of the Universe by numerically integrating the Friedmann equation, where the initial conditions for the expansion, acceleration and jerk parameters are taken from observational data.Comment: 18 pages, 4 figures, comments and references added to match accepted version; to appear in General Relativity and Gravitatio