Puzzle geometry and rigidity: The Fibonacci cycle is hyperbolic

Abstract

We describe a new and robust method to prove rigidity results in complex dynamics. The new ingredient is the geometry of the critical puzzle pieces: under control of geometry and ``complex bounds'', two generalized polynomial-like maps which admits a topological conjugacy, quasiconformal outside the filled-in Julia set are, indeed, quasiconformally conjugated. The proof uses a new abstract removability-type result for quasiconformal maps, following ideas of Heinonen & Koskela and Kallunki & Koskela, optimized to complex dynamics. As the first application to this new method, we prove that, for even criticalities distinct of two, the period two cycle of the Fibonacci renormalization operator is hyperbolic with one-dimensional unstable manifold. To derive the exponential contraction in the hybrid classes, we use the non existence of invariant line fields in the Fibonacci tower, the topological convergence (both results by van Strien & Nowicki) and a new argument, distinct of the C. McMullen and M. Lyubich previous methods in the classic renormalization operator theory. We also describe other future applications.