Isotropic singularities and isotropization in a class of Bianchi type-VI h cosmologies

The evolution of a class of exact spatially homogeneous cosmological models of Bianchi type VI_h is discussed. It is known that solutions of type VI_h cannot approach isotropy asymptotically at large times. Indeed the present class of solutions become asymptotic to an anisotropic vacuum plane wave solution. Nevertheless, for these solutions the initial anisotropy can decay, leading to a stage of finite duration in which the model is close to isotropy. Depending on the choice of parameters in the solution, this quasi-isotropic stage can commence at the initial singularity, in which case the singularity is of the type known as isotropic or Friedmann-like. The existence of this quasi-isotropic stage implies that these models can be compatible in principle with the observed universe.