Relative multisections of higher-dimensional manifolds with boundary
A multisection (as defined by Ben Aribi, Courte, Golla and Moussard) is a decomposition of a closed orientable manifold into model pieces. These model pieces are top-dimensional 1-handlebodies, whose subcollections intersect along 1-handlebodies of lower dimensions, and whose global intersection is a closed surface. This concept extends the notions of Heegaard splittings and trisections to higher dimensions. In this article, we adapt multisections to compact manifolds with boundary, generalizing sutured Heegaard splittings and relative trisections to every dimension. We define the associated diagrams, which encompass sutured Heegaard diagrams and relative trisection diagrams. A relative multisection induces a particular decomposition of the boundary of the manifold, which we call a relative fibration. We show that, in dimension n greater than 3, a connected manifold which relatively fibers is necessarily either a sphere, or a connected sum of copies of the product of the circle with the sphere of dimension n-1. We prove that a compact 5-manifold whose boundary relatively fibers admits a relative multisection. We also state a gluing theorem that allows to combine suitable relatively multisected manifolds with boundary into multisected closed manifolds.