Integrating infinite-dimensional Lie algebras by a Tannaka reconstruction (Part II)

Let g be a Lie algebra over a field F of characteristic zero, let C be a certain tensor category of representations of g, and C a certain category of duals. In [M 4] we associated to C and C by a Tannaka reconstruction a monoid M with a coordinate ring F [M ] of matrix coefficients, as well as a Lie algebra Lie(M). We interpreted the Tannaka monoid M algebraic geometrically as a weak algebraic monoid with Lie algebra Lie(M). The monoid M acts by morphisms of varieties on every object V of C. The Lie algebra Lie(M) acts on V by the differentiated action. In particular, we showed in [M 4]: If the Lie algebra g is generated by by one-parameter elements, then it identifies in a natural way with a subalgebra of Lie(M), and there exists a subgroup of the unit group of M , which is dense in M . In the present paper we introduce the coordinate ring of regular functions on this dense subgroup of M , as well as the algebra of linear regular functions on the universal enveloping algebra U(g) of g, and investigate their relation. We investigate and describe various coordinate rings of matrix coefficients associated to categories of integrable representations of g. We specialize to integrable representations of Kac-Moody algebras and free Lie algebras. Some results on coordinate rings of Kac-Moody groups obtained by V. G. Kac and D. Peterson, some coordinate rings of the associated groups of linear algebraic integrable Lie algebras defined by V. G. Kac, and some results on coordinate rings of free Kac-Moody groups obtained by Y. Billig and A. Pianzola fit into this context. We determine the Tannaka monoid associated to the full subcategory of integrable representations in the category O of a Kac-Moody algebra and to its category of full duals. Its Zariski-open dense unit group is the formal Kac-Moody group. We give various descriptions of its coordinate ring of matrix coefficients. We show that its Lie algebra is the formal Kac-Moody algebra. Mathematics Subject Classification 2000: 17B67, 22E65.