Cyclic homology of Hopf Galois extensions and Hopf algebras

Abstract

Let H be a Hopf algebra. By definition a modular crossed H-module is a vector space M on which H acts and coacts in a compatible way. To every modular crossed H-module M we associate a cyclic object Z(H,M). The cyclic homology of Z(H,M) extends the usual cyclic homology of the algebra structure of H, and the relative cyclic homology of an H-Galois extension. For a Hopf subalgebra K we compute, under some assumptions, the cyclic homology of an induced modular crossed module. As a direct application of this computation, we describe the relative cyclic homology of strongly graded algebras. In particular, we calculate the (usual) cyclic homology of group algebras and quantum tori. Finally, when H is the enveloping algebra of a Lie algebra, we construct a spectral sequence that converges to the cyclic homology of H with coefficients in an arbitrary modular crossed module. We also show that the cyclic homology of almost symmetric algebras is isomorphic to the cyclic homology of H with coefficients in a certain modular crossed-module.