On the parametrised Whitehead torsion of families of nearby Lagrangian submanifolds

Abstract

Motivated by the strong nearby Lagrangian conjecture, we constrain the parametrised Whitehead torsion of a family of closed exact Lagrangian submanifolds in a cotangent bundle. We prove the parametrised Whitehead torsion admits a factorisation through simpler maps, in particular implying it is trivial on $\pi_0$, $\pi_1$, and that its image is divisible by the Euler characteristic. We provide concrete implications for the Lagrangian monodromy question in the case of a high dimensional torus. This generalises earlier work of Abouzaid and Kragh \cite{AbKr} on the $\pi_0$ version, using different methods. Our main tool is the theory of twisted generating functions, building on \cite{ACGK}.