Journal of Symplectic Geometry

Volume 19 (2021)

Number 3

Functorial LCH for immersed Lagrangian cobordisms

Pages: 635 – 722



Yu Pan (Massachusetts Institute of Technology, Cambridge, Mass., U.S.A.)

Dan Rutherford (Department of Mathematical Sciences, Ball State University, Muncie, Indiana, U.S.A.)


For $1$-dimensional Legendrian submanifolds of $1$-jet spaces, we extend the functorality of the Legendrian contact homology DG-algebra (DGA) from embedded exact Lagrangian cobordisms, as in [16], to a class of immersed exact Lagrangian cobordisms by considering their Legendrian lifts as conical Legendrian cobordisms. To a conical Legendrian cobordism $\Sigma$ from $\Lambda_{-}$ to $\Lambda_{+}$, we associate an immersed DGA map, which is a diagram\[\mathcal{A}(\Lambda_{+}) \overset{f}{\to} \mathcal{A}(\Sigma) \overset{i}{\hookleftarrow} \mathcal{A}(\Lambda_{-}) \quad \textrm{,}\]where $f$ is a DGA map and $i$ is an inclusion map. This construction gives a functor between suitably defined categories of Legendrians with immersed Lagrangian cobordisms and DGAs with immersed DGA maps. In an algebraic preliminary, we consider an analog of the mapping cylinder construction in the setting of DG-algebras and establish several of its properties. As an application we give examples of augmentations of Legendrian twist knots that can be induced by an immersed filling with a single double point but cannot be induced by any orientable embedded filling.

Received 6 August 2019

Accepted 9 November 2020

Published 21 July 2021