Braids, conformal module and entropy

Abstract

In the work we discuss two invariants of conjugacy classes of braids. The first invariant is the conformal module which occurred in connection with the interest in the 13th Hilbert Problem. The second is a popular dynamical invariant, the entropy. It occurred in connection with Thurston's theory of surface homeomorphisms. We prove that these invariants are related: They are inverse proportional. This allows us on one hand to use known results on entropy for applications to the concept of conformal module, and on the other hand, to apply methods from quasi-conformal mappings to problems related to the entropy. In particular, we give a short conceptional proof of a theorem which appeared in connection with research on the Thirteen's Hilbert Problem. Mainly, we give applications of the concept of conformal module to the problem of the existence of homotopies (or isotopies, respectively) of continuous objects to the respective holomorphic objects, i.e. to Gromov's Oka Principle. We study objects involving braids and, more generally, continuous mappings from Riemann surfaces to complex manifolds, and focus on the case, when there are obstructions to Gromov's Oka Principle.