Orthogonally transitive G 2 cosmologies

The authors provide a new framework for analysing orthogonally transitive G 2 cosmologies, with a view to describing their asymptotic behaviour near the big bang and at late times. They assume a perfect fluid source with a linear equation of state and zero cosmological constant. The Einstein field equations are written as an autonomous system of first-order quasi-linear partial differential equations without constraints, in terms of dimensionless variables. The equilibrium points of this system are referred to as dynamical equilibrium states, and they show that the corresponding cosmological models are self-similar, but not necessarily spatially homogeneous.