Decomposable polytopes with few vertices

Abstract

A polytope $P$ is decomposable if it can be written as the Minkowski sum of two polytopes that are not homothetic to it. It is well known that decomposable $d$-dimensional polytopes with $2d$ or fewer vertices are the simplicial prisms. More recent work shows that, with two exceptions in low dimensions, decomposable $d$-dimensional polytopes with exactly $2d+1$ vertices are either pentasms or capped prisms. All these examples have a line segment for a summand. In this paper, we extend this conclusion to decomposable $d$-polytopes with exactly $2d+2$ or $2d+3$ vertices. In both cases, all such polytopes, with three exceptions, have a line segment for a summand. The exceptional cases are specified in detail.