Reeb orbits that force topological entropy

Abstract

We develop a forcing theory of topological entropy for Reeb flows in dimension $3$. A transverse link $L$ in a closed contact $3$-manifold $(Y,\xi)$ is said to force topological entropy if $(Y,\xi)$ admits a Reeb flow with vanishing topological entropy, and every Reeb flow on $(Y,\xi)$ realizing $L$ as a set of periodic Reeb orbits has positive topological entropy. Our main results establish topological conditions on a transverse link $L$ which imply that $L$ forces topological entropy. These conditions are formulated in terms of two Floer theoretical invariants: the cylindrical contact homology on the complement of transverse links introduced by Momin, and the strip Legendrian contact homology on the complement of transverse links. We then use these results to show that on every closed contact $3$-manifold that admits a Reeb flow with vanishing topological entropy, there exists transverse knots that force topological entropy.