Ideals of Rings of Differential Operators on Algebraic Curves (With an Appendix by George Wilson)

Let X be a complex smooth affine irreducible curve, and let D = D(X) be the ring of global differential operators on X. In this paper, we give a geometric classification of left ideals in $D$ and study the natural action of the Picard group of D on the space J(D) of isomorphism classes of such ideals. We recall that, up to isomorphism in the Grothendieck group K_0(D), the ideals of D are classified by the Picard group of X: there is a natural fibration \gamma: J(D) \to Pic(X), whose fibres are the stable isomorphism classes of ideals of D (see \cite{BW}). In this paper, we refine this classification by describing the fibres of \gamma in terms of finite-dimensional algebraic varieties C_n(X, I), which we call the (generalized) Calogero-Moser spaces. We define these varieties as representation varieties of deformed preprojective algebras over a certain extension of the ring of regular functions on $X$. As in the classical case (see \cite{Wi}), we prove that C_n(X, I) are smooth affine irreducible varieties of dimension 2n. Our results generalize the description of left ideals of the first Weyl algebra A_1© in \cite{BW1, BW2}; however, our methods are quite different.