Trisections of Nonorientable 4-Manifolds

Abstract

We study trisections of smooth compact nonorientable 4-manifolds and introduce trisections of nonorientable 4-manifolds with boundary. In particular, we prove a nonorientable analogue of a classical theorem of Laudenbach–Poénaru and analogues for some well-known theorems from 3-manifold topology. As a consequence, trisection diagrams and Kirby diagrams of closed nonorientable 4-manifolds exist. We discuss how the theory of trisections may be adapted to the setting of nonorientable 4-manifolds with many examples.