Toward cohomology rings of intersections of Peterson varieties and Richardson varieties

TL;DR

This paper investigates the (equivariant) cohomology rings of intersections between Peterson varieties and other subvarieties like Schubert and Richardson varieties, providing explicit calculations and presentations in type A.

Contribution

It extends the understanding of cohomology rings of Peterson varieties to their intersections with Schubert and Richardson varieties, offering explicit formulas and a technical framework.

Findings

Cohomology rings of Peterson-Schubert intersections identified with smaller Peterson varieties.

Explicit calculations of cohomology rings for Peterson-opposite Schubert intersections in type A.

Explicit presentations of cohomology rings for Peterson-Richardson intersections in type A.

Abstract

Peterson varieties are subvarieties of flag varieties and their (equivariant) cohomology rings are given by Fukukawa-Harada-Masuda in type A and soon later the author with Harada and Masuda gives an explicit presentation of the (equivariant) cohomology rings of Peterson varieties for arbitrary Lie types. In this note we study the (equivariant) cohomology ring of the intersections of Peterson variety with Schubert, opposite Schubert, and Richardson varieties in more general. By the work of Goldin-Mihalcea-Singh, the intersections of Peterson variety with Schubert varieties are naturally identified with smaller Peterson varieties, so the problem reduces to the problem for opposite Schubert intersections. In this note we provide a technical statement for (equivariant) cohomology ring of a subvariety with some conditions of Peterson variety. By using the statement, we calculate the (equivariant) cohomology rings for some intersections of Peterson varieties with opposite Schubert varieties in type A. We also explicitly present the (equivariant) cohomology rings for some intersections of Peterson varieties with Richardson varieties in type A.