Abstract
We prove the following higher-order Szegő theorem: If a measure on the unit circle has absolutely continuous part \(w(\theta )\) and Verblunsky coefficients \(\alpha \) with square-summable variation, then for any positive integer m,
is finite if and only if \(\alpha \in \ell ^{2m+2}\). This is the first known equivalence result of this kind in the regime of very slow decay, i.e., with \(\ell ^p\) conditions with arbitrarily large p. The usual difficulty of controlling higher-order sum rules is avoided by a new test sequence approach.
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Communicated by Vilmos Totik.
The author was partially supported by NSF Grant DMS-1301582.
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Lukic, M. On Higher-Order Szegő Theorems with a Single Critical Point of Arbitrary Order. Constr Approx 44, 283–296 (2016). https://doi.org/10.1007/s00365-015-9320-4
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DOI: https://doi.org/10.1007/s00365-015-9320-4