# Representation ring of Levi subgroups versus cohomology ring of flag varieties II

## TL;DR

This paper investigates a homomorphism connecting representation rings of Levi subgroups to cohomology rings of flag varieties for symplectic and orthogonal groups, proving injectivity in the limit for fixed parameters.

## Contribution

It extends the study of the representation ring to cohomology ring homomorphism for symplectic and orthogonal groups, establishing injectivity as the group size grows.

## Key findings

- Injectivity of the homomorphism for symplectic groups as n tends to infinity.
- Similar injectivity results for odd orthogonal groups.
- Provides a new link between representation theory and topology of flag varieties.

## Abstract

For any reductive group G and a parabolic subgroup P with its Levi subgroup L, the first author in [Ku2] introduced a ring homomorphism $ \xi^P_\lambda: Rep^\mathbb{C}_{\lambda-poly}(L) \to H^*(G/P, \mathbb{C})$, where $ Rep^\mathbb{C}_{\lambda-poly}(L)$ is a certain subring of the complexified representation ring of L (depending upon the choice of an irreducible representation $V(\lambda)$ of G with highest weight $\lambda$). In this paper we study this homomorphism for G=Sp(2n) and its maximal parabolic subgroups $P_{n-k}$ for any $1\leq k\leq n$ (with the choice of $V(\lambda) $ to be the defining representation $V(\omega_1) $ in $\mathbb{C}^{2n}$). Thus, we obtain a $\mathbb{C}$-algebra homomorphism $ \xi_{n,k}: Rep^\mathbb{C}_{\omega_1-poly}(Sp(2k)) \to H^*(IG(n-k, 2n), \mathbb{C})$. Our main result asserts that $ \xi_{n,k}$ is injective when n tends to $\infty$ keeping k fixed. Similar results are obtained for the odd orthogonal groups.