On the transverse invariant and braid dynamics

Abstract

Suppose $(B,\pi )$ is an open book supporting $(Y,\xi )$, where the binding $B$ is possibly disconnected, and $K$ is a braid about this open book. Then $B\cup K$ is naturally a transverse link in $(Y,\xi )$. We prove that the transverse link invariant in knot Floer homology, \[\widehat{t}(B\cup K)\in \widehat{HFK}(-Y,B\cup K),\] defined in [BVV13] is always nonzero. This generalizes the main results of Etnyre and Vela-Vick in [VV11, EVV10]. As an application, we show that if $K$ is braided about an open book with connected binding, and has fractional Dehn twist coefficient greater than one, then $\hat{t}(K)\ne 0$. This generalizes a result of Plamenevskaya [PLA15] for classical braids.

Version 2: Added comultiplication of transverse invariant for minus version of knot Floer homology. Revised proofs of main results do not rely on naturality of the transverse invariant under contact +1 surgery, nor any surgery exact triangles