2010/02/20 by Olmo, Gonzalo J., Sanchis-Alepuz, Helios, Tripathi, Swapnil
#FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc)
paper · doi:10.48550/arxiv.1002.3920
We show that extended theories of gravity with Lagrangian f(R,RμνRμν) in the Palatini formulation possess a phenomenology much richer than the simpler f(R) or f(RμνRμν) theories. In fact, we find that the scalars R and Q=RμνRμν can be written as algebraic functions of the energy density and pressure of the energy momentum tensor. In the simpler cases of f(R) or f(RμνRμν) theories, R and Q are just functions of the trace T of the energy-momentum tensor. As a result, in radiation dominated universes f(R) and f(RμνRμν) theories exhibit the same dynamics as general relativity with an effective cosmological constant. This is not the case of f(R,RμνRμν) models, in which R=R(ρ,P) and Q=Q(ρ,P) and, therefore, modified dynamics exists even for traceless sources.