Flat Friedmann cosmologies with stiff fluid in Einstein–Cartan theory

Abstract

Flat Friedmann cosmologies with stiff fluid are considered in the framework of the Einstein–Cartan theory. The version of this theory which simultaneously takes into consideration two sources of torsion, namely, a perfect fluid with the vacuum equation of state and a nonminimally coupled scalar field, is studied. It is demonstrated that, for bouncing models, phantom cosmologies with and without a Big Rip singularity are possible. Singular expanding models are presented where the early stages are dominated by a scalar-torsion field which behaves as an ultrastiff fluid, while the late stages are dominated by a perfect fluid which causes a de Sitter asymptotic. Some cosmological consequences of two sources of torsion are discussed.