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On the non-attractive character of gravity in f(R) theories

By F. D. Albareti, José Alberto Ruiz Cembranos, Álvaro de la Cruz Dombriz and Antonio Dobado González

Abstract

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.\u

Topics: Física
Publisher: Iop Publishing Ltd
Year: 2020
DOI identifier: 10.1088/1475-7516
OAI identifier: oai:www.ucm.es:22935
Provided by: EPrints Complutense
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