Minimal triangulations of circle bundles

Abstract

A triangulation of a circle bundle $ E \xrightarrow[\text{}]{\pi} B$ is a triangulation of the total space $E$ and the base $B$ such that the projection $\pi$ is a simplicial map. In the paper we address the following questions: Which circle bundles can be triangulated over a given triangulation of the base? What are the minimal triangulations of a bundle? A complete solution for semisimplicial triangulations was given by N. Mn\"{e}v. Our results deal with classical triangulations, that is, simplicial complexes. We give an exact answer for an infinite family of triangulated spheres (including the boundary of the $3$-simplex, the boundary of the octahedron, the suspension over an $n$-gon, the icosahedron). For the general case we present a sufficient criterion for existence of a triangulation. Some minimality results follow straightforwadly.