Boundedness, compactness, and invariant norms for Banach cocycles over   hyperbolic systems
  We consider group-valued cocycles over dynamical systems with hyperbolic behavior. The base system is either a hyperbolic diffeomorphism or a mixing subshift of finite type. The cocycle $A$ takes values in the group of invertible bounded linear operators on a Banach space and is H\"older continuous. We consider the periodic data of $A$, i.e. the set of its return values along the periodic orbits in the base. We show that if the periodic data of $A$ is uniformly quasiconformal or bounded or contained in a compact set, then so is the cocycle. Moreover, in the latter case the cocycle is isometric with respect to a H\"older continuous family of norms. We also obtain a general result on existence of a measurable family of norms invariant under a cocycle. 
Boris Kalinin and Victoria Sadovskaya
math.DS