Equivariant multiplicities of simply-laced type flag minors

Abstract:

Let $\mathfrak {g}$ be a finite simply-laced type simple Lie algebra. Baumann-Kamnitzer-Knutson recently defined an algebra morphism $\overline {D}$ on the coordinate ring $\mathbb {C}[N]$ related to Brion’s equivariant multiplicities via the geometric Satake correspondence. This map is known to take distinguished values on the elements of the MV basis corresponding to smooth MV cycles, as well as on the elements of the dual canonical basis corresponding to Kleshchev-Ram’s strongly homogeneous modules over quiver Hecke algebras. In this paper we show that when $\mathfrak {g}$ is of type $A_n$ or $D_4$, the map $\overline {D}$ takes similar distinguished values on the set of all flag minors of $\mathbb {C}[N]$, raising the question of the smoothness of the corresponding MV cycles. We also exhibit certain relations between the values of $\overline {D}$ on flag minors belonging to the same standard seed, and we show that in any $ADE$ type these relations are preserved under cluster mutations from one standard seed to another. The proofs of these results partly rely on Kang-Kashiwara-Kim-Oh’s monoidal categorification of the cluster structure of $\mathbb {C}[N]$ via representations of quiver Hecke algebras.