Singularity avoidance in quantum FRW cosmologies in the presence of barotropic perfect fluids

Recently, an effective formulation of gravity which lies in between the Wheeler-DeWitt approach and classical cosmology was discussed. It was shown that the Big Bang singularity of FRW cosmologies is avoided in a quite natural way. Here, we aim to prove that this formulation is able to avoid the Big Rip singularity too, in contradistinction with Schutz's formalism as applied to quantum cosmological perfect fluids. Actually, in using this last formalism, some authors have argued that such singularity would persist even after quantization, however, what we carried out, with our formulation as a guide, proved not to be the case. Also, it will be argued that it is the implicit regularization of the classical Hamiltonian performed in loop quantum cosmology, which is needed in loop cosmology in order to build a well-defined quantum (discrete) theory, which avoids the Big Rip singularity in that theory, this mechanism being different from other, ordinarily invoked quantum effects. © 2009 IOP Publishing Ltd.