Published online by Cambridge University Press: 04 August 2020
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
${cCFL^-(D)}$ 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.