Quasifinite representations of classical Lie subalgebras of W∞, p

Abstract

We show that there are exactly two anti-involutions σ± of the algebra of differential operators on the circle that are a multiple of p(t∂t) preserving the principal gradation (p∈C[x]p∈C[x] non-constant). We classify the irreducible quasifinite highest weight representations of the central extension Dˆ±pD̂p± of the Lie subalgebra fixed by −σ±. The most important cases are the subalgebras Dˆ±xD̂x± of W∞ that are obtained when p(x) = x. In these cases, we realize the irreducible quasifinite highest weight modules in terms of highest weight representation of the central extension of the Lie algebra of infinite matrices with finitely many nonzero diagonals over the algebra C[u]/(um+1)C[u]/(um+1) and its classical Lie subalgebras of C and D types.