 10129 Milivoje Lukic
 Orthogonal Polynomials with Recursion Coefficients of Generalized Bounded Variation
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Aug 24, 10

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Abstract. We consider probability measures on the real line or unit circle with Jacobi or Verblunsky coefficients satisfying an $\ell^p$ condition and a generalized bounded variation condition. This latter condition requires that a sequence can be expressed as a sum of sequences $eta^{(l)}$, each of which has rotated bounded variation, i.e., $\sum_{n=0}^\infty  e^{i\phi_l} eta_{n+1}^{(l)}  eta_n^{(l)} $ is finite for some $\phi_l$. This includes discrete Schr\"odinger operators on a halfline or line with finite linear combinations of Wignervon Neumann type potentials.
For the real line, we prove that in the Lebesgue decomposition $d\mu=f dm + d\mu_s$ of such measures, the intersection of (2,2) with the support of $d\mu_s$ is contained in an explicit finite set S (thus, $d\mu$ has no singular continuous part), and f is continuous and nonvanishing on $(2,2) \setminus S$. The results for the unit circle are analogous, with (2,2) replaced by the unit circle.
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