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

Land Titling and Power Building in the Three Regimes of Ethiopia: The Last Empire, the First Republic, and the Second Republic

Land is not a mere physical resource in Ethiopia; rather it has a strong tie with social values and political power. Apparently, scholars in this particular area have largely focued on the residual effects of land dispossessions and the harsh incursions into the communal sanctities. Moreover, they paid an enormous attention to the effects of land grabbing on the economic, social and human rights of individuals. However, this article argues that less attention has been given to the role of land titlting in buiding the power of political elites in Ethiopia. In order to explore this, the article attempted to anlyze the three regimes in Ethiopia- the Emperial, Derg, and  EPRDF- and their land entitlment strategies as a means of power making and legitimization of the establishments. The artilce, thus, concludes that there have been a strong connection between land and power in the three regimes of Ethiopia and it maintains that land tilting strategies have been extensively used for the political interests and power grabbing objectives of the regimes. Keywords: Ethiopia, Land Policy, Land titling, Land Tenure, Power building DOI: 10.7176/JCSD/55-02 Publication date: January 31st 202

Inflationary f(R) cosmologies

This paper discusses a simple procedure to reconstruct f (R)-gravity models from exact cosmological solutions of the Einstein field equations with a noninteracting classical scalar field-and-radiation background. From the kind of inflationary scenario we want, we show how the potential functions can be obtained. We then show how an f (R) gravitational Lagrangian density that mimics the same cosmological expansion as the scalar field-driven inflation of General Relativity can be reconstructed. As a demonstration, we calculate the slow-roll parameters (the spectral index n s and the tensor-to-scalar ratio r) and compare them to the Planck data.Comment: 13 pages, 10 figure

Simultaneous expansion and rotation of shear-free universes in modified gravity

We show in a fully covariant way that, there exist a class of $f(R)$ models for which a shear-free, almost FLRW universe can expand and rotate at the same time .Comment: 4 pages, no figures. Contribution submitted to the proceedings of the Spanish Relativity Meeting ERE2011, September 2011, Madrid, Spai