On the center of the small quantum group

Abstract

Using the quantum Fourier transform F, we describe the block decomposition and multiplicative structure of a subalgebra Z + F(Z) in the center of the small quantum group u_l at a root of unity. It contains the previously known subalgebra Z, which is isomorphic to the algebra of characters of finite dimensional modules over u_l. We prove that the intersection $Z \cap F(Z)$ coincides with the annihilator of the radical of Z. The whole center of u_l coincides with the obtained subalgebra Z + F(Z) in case of sl_2, and is bigger than that in general.