Lie algebra cohomology of the positive part of twisted affine Lie algebras

Abstract: The explicit Verlinde formula for the dimension of conformal blocks, attached to a marked projective curve $\Sigma$, a simple Lie algebra $\mathfrak{g}$ over $\mathbb{C}$ and integrable highest weight modules of a fixed central charge of the corresponding affine Lie algebra $\hat{L}(\mathfrak{g})$ attached to the marked points, requires (among several other important ingredients) a Lie algebra cohomology vanishing result due to C. Teleman for the positive part $\hat{L}^+(\mathfrak{g})$ with coefficients in the tensor product of an integrable highest weight module with copies of finite dimensional evaluation modules. The aim of this paper is to extend this result of Teleman to a twisted setting where $\mathfrak{g}$ is endowed with a special automorphism $\sigma$ and the curve $\Sigma$ is endowed with the action of $\sigma$. In this general setting, the affine Lie algebra gets replaced by twisted affine Lie algebras. The crucial ingredient (as in Teleman) is to prove a certain Nakano Identity.