%0 Journal Article
%A Albareti, F. D.
%A Ruiz Cembranos, José Alberto
%A Cruz Dombriz, Álvaro de la
%A Dobado González, Antonio
%T On the non-attractive character of gravity in f(R) theories
%D 2013
%@ 1475-7516
%U https://hdl.handle.net/20.500.14352/33349
%X Raychaudhuri equation is found provided that particular energy conditions are assumed and regardless the considered solution of the Einstein's equations. This fact is usually interpreted as a manifestation of the attractive character of gravity. Nevertheless, a positive contribution to Raychaudhuri equation from space-time geometry should occur since this is the case in an accelerated expanding Robertson-Walker model for congruences followed by fundamental observers. Modified gravity theories provide the possibility of a positive contribution although the standard energy conditions are assumed. We address this important issue in the context of f(R) theories, deriving explicit upper bounds for the contribution of space-time geometry to the Raychaudhuri equation. Then, we examine the parameter constraints for some paradigmatic f(R) models in order to ensure a positive contribution to this equation. Furthermore, we consider the implications of these upper bounds in the equivalent formulation of f(R) theories as a Brans-Dicke model.
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