Semigroups of holomorphic functions; rectifiability and Lipschitz properties of the orbits

Abstract

Let $(\ddot{I}{•}_t)$ be a semigroup of holomorphic functions in the unit disk. We prove that all its orbits are rectifiable and that its forward orbits are Lipschitz curves. Moreover, we find a necessary and sufficient condition in terms of hyperbolic geometry so that a backward orbit is a Lipschitz curve. We further explore the Lipschitz condition for forward orbits lying on the unit circle and then for semigroups of holomorphic functions in general simply connected domains.

31 pages, 2 figures, to appear in Canadian Journal of Mathematics