Asymptotics of the L2 norm of derivatives of OPUC

Abstract

We show that for many families of OPUC, one has k'′nk2/n → 1, , a condition we call normal behavior. We prove that this implies | n| → 0 and that it holds if P∞ n=0| n| < ∞. We also prove it is true for many sparse sequences. On the other hand, it is often destroyed by the insertion of a mass point.