Geometry of generating functions and Lagrangian spectral invariants

Abstract

Partially motivated by the study of topological Hamiltonian dynamics, we prove various $C^0$-aspects of the Lagrangian spectral invariants and the basic phase functions $f_H$, that is, a natural graph selector constructed by Lagrangian Floer homology of $H$ (relative to the zero section $o_N$). In particular, we prove that $$ \gamma^{lag}(\phi_H^1(o_N)): = \rho^{lag}(H;1) - \rho^{lag}(H;[pt]^\#) \to 0 $$ as $\phi_H^1 \to id$, \emph{provided} $H$'s satisfy $\supp X_H \subset D^R(T^*N) \setminus o_B$ for some $R > 0$ and a closed subset $B \subset N$ with nonempty interior. We also study the relationship between $f_H$ and $\rho^{lag}(H;1)$ and prove a structure theorem of the micro-support of the singular locus $\Sing(\sigma_H)$ of the function $f_H$. Based on this structure theorem and a classification theorem of generic Lagrangian singularity in $\dim N = 2$ obtained by Arnold's school, we define the notion of cliff-wall surgery when $\dim N = 2$: the surgery replaces a multi-valued Lagrangian graph $\phi_H^1(o_N)$ by a piecewise-smooth Lagrangian cycle that is canonically constructed out of the single valued branch $\Sigma_H: = \Graph df_H \subset \phi_H^1(o_N)$ defined on an open dense subset of $N \setminus \Sing(\sigma_H)$ of codimension 1.