1997/12/02 by Sergey Arkhipov, Arkhipov, Sergey
Mathematics · #Advanced Algebra and Geometry #Advanced Topics in Algebra #Algebraic structures and combinatorial models #FOS: Mathematics #Quantum Algebra (math.QA) #math.QA #q-alg
paper · pdf · doi:10.48550/arxiv.q-alg/9712010
22 pages, LaTeX 2e
arxiv created 1997/12/02 · openalex publication_date 1997/12/02 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The paper is devoted to the proof of the following conjecture due to B. Feigin. Let \frak u_ℓ be the small quantum group a the primitive ℓ-th root of unity. Then it is known that the usual Ext algebra of the trivial \frak u_ℓ-module is isomorphic to the algebra of regular functions on the nilpotent variety \cal N in the corresponding simple Lie algebra \frak g (see [GK]). Consider semiinfinite cohomology of the trivial \frak u_ℓ-module introduced in [Ar1], [Ar2]. It was shown in [Ar2] that the Ext algebra of the trivial \frak u_ℓ-module acts naturally on semiinfinite cohomology. Moreover semiinfinite cohomology space of the trivial \frak_ℓ-module is equipped with a natural \frak g-module structure. B. Feigin conjectured that the described \frak g-module and F(\cal N)-module structures coincide with the ones on the space of local cohomology of the structure sheaf on \cal N with support in the standard positive nilpotent subalgebra \frak n+⊂\cal N⊂ \frak g. We give a detailed proof of the conjecture. Moreover we generalize the statement and describe semiinfinite cohomology of contragradient Weyl modules in terms of local cohomology of certain coherent sheaves on the nilpotent cone and on its desingularization T^*(G/B). To do this we construct a certain specialization of the quantum BGG resolution of the simple module L(λ) defined for generic values of the quantizing parameter into the root of unity called the quasi-BGG complex. The complex conists of direct sums of quasi-Verma modules and provides conjecturally a resolution of the Weyl module W(λ).