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

Abstract

We introduce a generalization of the Lisca-Ozsváth-Stipsicz-Szabó 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 $cCF{L}^{-}(D)$ 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.