We give a new proof of an unpublished result of Dale Peterson, proved by Lam and Shimozono, which identifies explicitly the structure constants, with respect to the quantum Schubert basis, for the T-equivariant quantum cohomology
$QH^{\bullet }_T(G/P)$ of any flag variety
$G/P$ with the structure constants, with respect to the affine Schubert basis, for the T-equivariant Pontryagin homology
$H^T_{\bullet }(\mathcal {G}r)$ of the affine Grassmannian
$\mathcal {G}r$ of G, where G is any simple simply-connected complex algebraic group.
Our approach is to construct an
$H_T^{\bullet }(pt)$-algebra homomorphism by Gromov-Witten theory and show that it is equal to Peterson’s map. More precisely, the map is defined via Savelyev’s generalized Seidel representations, which can be interpreted as certain Gromov-Witten invariants with input
$H^T_{\bullet }(\mathcal {G}r)\otimes QH_T^{\bullet }(G/P)$. We determine these invariants completely, in a way similar to how Fulton and Woodward did in their proof of the quantum Chevalley formula.