Kasner and mixmaster behavior in universes with equation of state w≥1 -: art. no. 063514

We consider cosmological models with a scalar field with equation of state wgreater than or equal to1 that contract towards a big crunch singularity, as in recent cyclic and ekpyrotic scenarios. We show that chaotic mixmaster oscillations due to anisotropy and curvature are suppressed, and the contraction is described by a homogeneous and isotropic Friedmann equation if w>1. We generalize the results to theories where the scalar field couples top forms and show that there exists a finite value of w, depending on the p-forms, such that chaotic oscillations are suppressed. We show that Z(2) orbifold compactification also contributes to suppressing chaotic behavior. In particular, chaos is avoided in contracting heterotic M-theory models if w>1 at the crunch.