Kostant's problem, Goldie rank and the Gelfand-Kirillov conjecture
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- Joseph, A. Invent Math (1980) 56: 191. doi:10.1007/BF01390044
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Let g be a complex semisimple Lie algebra andU(g) its enveloping algebra. GivenM a simpleU(g) module, letL(M, M) denote the subspace of ad g finite elements of Hom(M, M). Kostant has asked if the natural homomorphism ofU(g) intoL(M, M) is surjective. Here the question is analysed for simple modules with a highest weight vector. This has a negative answer if g admits roots of different length (, 6.5). Here general conditions are obtained under whichU(g)/AnnM andL(M, M) have the same ring of fractions—in particular this is shown to always hold if g has only typeAn factors. Combined with , this provides a method for determining the Goldie ranks for the primitive quotients ofU(g). Their precise form is given in typeAn (Cartan notation) for which the generalized Gelfand-Kirillov conjecture for primitive quotients is also established.