Bounds on the $f$-Vectors of Tight Spans

Abstract

The tight span $T_d$ of a metric $d$ on a finite set is the subcomplex of bounded faces of an unbounded polyhedron defined by~$d$. If $d$ is generic then $T_d$ is known to be dual to a regular triangulation of a second hypersimplex. A tight upper and a partial lower bound for the face numbers of $T_d$ (or the dual regular triangulation) are presented.