Return to Revisions

Complex powers of line bundles are classes in H^{1,1}, or equivalently sheaves of twisted differential operators (TDO) (let's work in the complex topology). This maps to H^2 with C coefficients, or modding out by Z-cohomology, to H^2 with C^x coefficients (sorry don't know how to tex here..) The latter classifies C^x gerbes, ie gerbes with a flat connection (usual gerbes can be described by H^2(X,O^x)). Note that honest line bundles give the trivial gerbe. In fact the category of modules over a TDO only depends on the TDO up to tensoring with line bundles --- ie it only depends on the underlying gerbe, and can be described as ordinary D-modules on the gerbe. Or if you prefer, regular holonomic modules over a TDO are the same as perverse sheaves on the underlying gerbe. This is explained eg in the encyclopedic Chapter 7 of Beilinson-Drinfeld's Quantization of Hitchin Hamiltonians document, or I think also in a paper of Kashiwara eg in the 3-volume Asterisque on singularities and rep theory (and maybe even his recent D-modules book). B&D talk in terms of crystalline O^x gerbes rather than C^x gerbes but the story is the same.