On Hopf algebras whose coradical is a cocentral abelian cleft extension

Abstract

This paper is a first step toward the full description of a family of Hopf algebras whose coradical is isomorphic to a semisimple Hopf algebra K_{n}, n an odd positive integer, obtained by a cocentral abelian cleft extension. We describe the simple Yetter-Drinfeld modules, compute the fusion rules and determine the finite-dimensional Nichols algebras for some of them. In particular, we give the description of the finite-dimensional Nichols algebras over simple modules over K_{3}. This includes a family of 12-dimensional Nichols algebras $B_\xi$ depending on 3rd roots of unity. Here, $B_{1}$ is isomorphic to the well-known Fomin-Kirillov algebra, and $B_{\xi} \simeq B_{\xi^{2}} $ as graded algebras but $B_1$ is not isomorphic to $B_{\xi} $ as algebra for $\xi\neq 1$. As a byproduct we obtain new Hopf algebras of dimension 216.