Minimal semisimple Hessenberg schemes

Abstract

We study a collection of Hessenberg varieties in the type A flag variety associated to a nonzero semisimple matrix whose conjugacy class has minimal dimension. We prove each such minimal semisimple Hessenberg variety is a union Richardson varieties and compute this set of Richardson varieties explicitly. Our methods leverage the notion of matrix Hessenberg schemes to answer questions about the geometry of minimal semisimple Hessenberg varieties using commutative algebra and known results on Schubert determinantal ideals. In particular, we show that all type A minimal semisimple matrix Hessenberg schemes are reduced.