Asymptotic self-similarity breaking at late times in cosmology

We study the late-time evolution of a class of exact anisotropic cosmologic al solutions of Einstein's equations, namely spatially homogeneous cosmolog ies of Bianchi type VII0 with a perfect fluid source. We show that, in cont rast to models of Bianchi type VIIh which are asymptotically self-similar a t late times, Bianchi VII0 models undergo a complicated type of selfsimilar ity breaking. This symmetry breaking affects the late-time isotropization t hat occurs in these models in a significant way: if the equation of state p arameter gamma satisfies gamma less than or equal to 4/3 the models isotrop ize as regards the shear but not as regards the Weyl curvature. Indeed, the se models exhibit a new dynamical feature that we refer to as Weyl curvatur e dominance: the Weyl curvature dominates the dynamics at late times. By vi ewing the evolution from a dynamical systems perspective we show that, desp ite the special nature of the class of models under consideration, this beh aviour has implications for more general models.