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  • Equivariant homology and K-...
    Bezrukavnikov, Roman; Finkelberg, Michael; Mirković, Ivan

    Compositio mathematica, 05/2005, Letnik: 141, Številka: 3
    Journal Article

    For an almost simple complex algebraic group G with affine Grassmannian $\text{Gr}_G=G(\mathbb{C}(({\rm t})))/G(\mathbb{C}{\rm t})$, we consider the equivariant homology $H^{G(\mathbb{C}{\rm t})}(\text{Gr}_G)$ and K-theory $K^{G(\mathbb{C}{\rm t})}(\text{Gr}_G)$. They both have a commutative ring structure with respect to convolution. We identify the spectrum of homology ring with the universal group-algebra centralizer of the Langlands dual group $\check G$, and we relate the spectrum of K-homology ring to the universal group-group centralizer of G and of $\check G$. If we add the loop-rotation equivariance, we obtain a noncommutative deformation of the (K-)homology ring, and thus a Poisson structure on its spectrum. We relate this structure to the standard one on the universal centralizer. The commutative subring of $G(\mathbb{C}{\rm t})$-equivariant homology of the point gives rise to a polarization which is related to Kostant's Toda lattice integrable system. We also compute the equivariant K-ring of the affine Grassmannian Steinberg variety. The equivariant K-homology of GrG is equipped with a canonical basis formed by the classes of simple equivariant perverse coherent sheaves. Their convolution is again perverse and is related to the Feigin–Loktev fusion product of $G(\mathbb{C}{\rm t})$-modules.