The set of fiber-bunched cocycles with nonvanishing Lyapunov exponents over a partially hyperbolic map is open

Abstract

We prove that the set of fiber-bunched SL(2, R)-valued Hölder cocycles with nonvanishing Lyapunov exponents over a volume preserving, accessible and center-bunched partially hyperbolic diffeomorphism is open. Moreover, we present an example showing that this is no longer true if we do not assume accessibility in the base dynamics.