Universal deformation formulas and braided module algebras

Abstract

We study formal deformations of a crossed product S ( V ) # f G , of a polynomial algebra with a group, induced from a universal deformation formula introduced by Witherspoon. These deformations arise from braided actions of Hopf algebras generated by automorphisms and skew derivations. We show that they are non-trivial in the characteristic free context, even if G is infinite, by showing that their infinitesimals are not coboundaries. For this we construct a new complex which computes the Hochschild cohomology of S ( V ) # f G .