Unbounded Widom factors for orthogonal and residual polynomials
Abstract
We study Widom factors for (a) monic orthogonal polynomials in with respect to the equilibrium measure of a compact set and (b) residual polynomials normalized at an exterior point. Using weakly equilibrium Cantor sets , we prove: (1) Given any sequence with subexponential growth, there exists a non-polar Cantor set , depending on , such that the Widom factors of the associated orthogonal polynomials (with respect to the equilibrium measure of ) exceed for every . (2) For the same built from and each exterior point , the residual Widom factors satisfy power-type lower bounds with a Harnack-distance exponent : they are bounded below by for all degrees when lies in an unbounded gap, and along a subsequence of degrees when lies in a bounded gap. Consequently, if, in addition, is monotone increasing and unbounded, then the sequence of residual Widom factors is unbounded for every . The proofs combine inverse-image constructions, capacity comparisons for period- sets, harmonic-measure representations for differences of Green functions, and alternation principles on nested approximants.
Keywords
Cite
@article{arxiv.2508.15131,
title = {Unbounded Widom factors for orthogonal and residual polynomials},
author = {Gökalp Alpan},
journal= {arXiv preprint arXiv:2508.15131},
year = {2025}
}