Lecture notes on trisections and cohomology

Abstract

In these notes, we describe several geometric interpretations of $H^2(X)$ when $X$ is a trisected 4-manifold. The main insight is that, by analogy with Hodge theory and sheaf cohomology in algebraic geometry, classes in $H^2(X)$ can be usefully interpeted as $"(1,1)"$-classes. These notes formed the first half of an aborted seminar on symplectic trisections at the Max Planck Institute for Mathematics during Spring 2020.