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Higher-Order Szego Theorems With Two Singular Points

Mathematical Physics 2007-05-23 v1 Classical Analysis and ODEs math.MP

Abstract

We consider probability measures, dμ=w(θ)\fdθ2π+dμ\sd\mu=w(\theta) \f{d\theta}{2\pi} +d\mu_\s, on the unit circle, \bbD\partial\bbD, with Verblunsky coefficients, {αj}j=0\{\alpha_j\}_{j=0}^\infty. We prove for θ1θ2\theta_1\neq\theta_2 in [0,2π)[0,2\pi) and (δβ)j=βj+1(\delta\beta)_j=\beta_{j+1} that [1cos(θθ1)][1cos(θθ2)]logw(θ)\fdθ2π> \int [1-\cos(\theta-\theta_1)][1-\cos(\theta-\theta_2)] \log w(\theta) \f{d\theta}{2\pi} >-\infty if and only if j=0{(δeiθ2)(δeiθ1)α}j2+\absαj4< \sum_{j=0}^\infty \bigl|\bigl\{(\delta -e^{-i\theta_2}) (\delta -e^{-i\theta_1}) \alpha\bigr\}_j\bigr|^2 +\abs{\alpha_j}^4 <\infty We also prove that (1cosθ)2logw(θ)\fdθ2π> \int (1-\cos\theta)^2 \log w(\theta) \f{d\theta}{2\pi} >-\infty if and only if j=0\absαj+22αj+1+αj2+\absαj6< \sum_{j=0}^\infty \abs{\alpha_{j+2}-2\alpha_{j+1} +\alpha_j}^2 + \abs{\alpha_j}^6 <\infty

Cite

@article{arxiv.math-ph/0409065,
  title  = {Higher-Order Szego Theorems With Two Singular Points},
  author = {Barry Simon and Andrej Zlatos},
  journal= {arXiv preprint arXiv:math-ph/0409065},
  year   = {2007}
}