Efficient multisections of odd-dimensional tori

Abstract

Rubinstein--Tillmann generalized the notions of Heegaard splittings of 3-manifolds and trisections of 4-manifolds by defining {\it multisections} of PL $n$-manifolds, which are decompositions into $k=\lfloor n/2\rfloor +1$ $n$-dimensional 1-handlebodies with nice intersection properties. For each odd-dimensional torus $T^n$, we construct a multisection which is {\it efficient} in the sense that each 1-handlebody has genus $n$, which we prove is optimal; each multisection is {\it symmetric} with respect to both the permutation action of $S_n$ on the indices and the ${\mathbb{Z}}_k$ translation action along the main diagonal. We also construct such a trisection of $T^4$, lift all symmetric multisections of tori to certain cubulated manifolds, and obtain combinatorial identities as corollaries.

65 pages, 16 figures, 21 tables, to appear in Algebraic & Geometric Topology. It remains an open question whether every smooth manifold admits a smooth multisection