Minimum depth of double cross product extensions

Abstract

In this paper we explore minimum odd and minimum even depth sub- algebra pairs in the context of double cross products of finite dimensional Hopf algebras. We start by defining factorization algebras and outline how subring depth in this context relates with the module depth of the regular left module representation of the given subalgebra. Next we study minimum odd depth for double cross product Hopf subalgebras and determine their value in terms of their related module depth, we conclude that minimum odd depth of Drinfel’d double Hopf subalgebras is 3. Finaly we produce a necessary and sufficient condition for depth 2 in double cross product Hopf subalgebra extensions. This sufficient condition is then used to prove results regarding minimum depth 2 in Drinfel’d double Hopf subalgebras, particu- larly in the case of finite Group Hopf algebras. Lastly we provide formulas for the centralizer of a normal Hopf subalgebra in a double cross product scenario.