Realization Spaces of Uniform Phased Matroids

Abstract

A phased matroid is a matroid with additional structure which plays the same role for complex vector arrangements that oriented matroids play for real vector arrangements. The realization space of an oriented (resp., phased) matroid is the space of vector arrangements in $\mathbb R^n$ (resp., $\mathbb C^n$) that correspond to oriented (resp., phased) matroid, modulo a change of coordinates. According to Mn\"ev's Universality Theorem, the realization spaces of uniform oriented matroids with rank greater than or equal to $3$ can be as complicated as any open semi-algebraic variety. In contrast, uniform phased matroids which are not essentially oriented have remarkably simple realization spaces if they are uniform. We also present a criterion for realizability of uniform phased matroids that are not essentially oriented.