An invariant of Legendrian and transverse links from open book decompositions of contact 3-manifolds

TL;DR

This paper generalizes a Legendrian link invariant to rational homology spheres using open book decompositions and link Floer homology, providing tools for distinguishing Legendrian links and analyzing non-loose links.

Contribution

It introduces a new Legendrian invariant for links in rational homology spheres via open book decompositions and link Floer homology, extending previous invariants.

Findings

Defines a chain complex cCFL^-(D) with a special cycle for Legendrian links

Proves invariance of the invariant under Legendrian isotopy via chain maps

Establishes a connected sum formula and applications to non-loose Legendrian links

Abstract

We introduce a generalization of the Lisca-Ozsv\'ath-Stipsicz-Szab\'o Legendrian invariant $\mathfrak L$ to links in every rational homology sphere, using the collapsed version of link Floer homology. We represent a Legendrian link $L$ in a contact 3-manifold $(M,\xi)$ with a diagram $D$, given by an open book decomposition of $(M,\xi)$ adapted to $L$, and we construct a chain complex $cCFL^-(D)$ with a special cycle in it denoted by $\mathfrak L(D)$. Then, given two diagrams $D_1$ and $D_2$ which represent Legendrian isotopic links, we prove that there is a map between the corresponding chain complexes, that induces an isomorphism in homology and sends $\mathfrak L(D_1)$ into $\mathfrak L(D_2)$. Moreover, a connected sum formula is also proved and we use it to give some applications about non-loose Legendrian links; that are links such that the restriction of $\xi$ on their complement is tight.