On the leading coefficient of polynomials orthogonal over domains with corners

Abstract

Let $G$ be the interior domain of a piecewise analytic Jordan curve without cusps. Let $\{p_n{\}}_{n=0}^{\infty }$ be the sequence of polynomials that are orthonormal over $G$ with respect to the area measure, with each $p_n$ having leading coefficient ${\lambda }_n>0$. N. Stylianopoulos has recently proven that the asymptotic behavior of ${\lambda }_n$ as $n\to \infty$ is given by \[ \frac{n+1}π\frac{γ^{2n+2}}{ λ_n^{2}}=1-α_n, \] where ${\alpha }_n=O(1/n)$ as $n\to \infty$ and $\gamma$ is the reciprocal of the logarithmic capacity of the boundary $\partial G$. In this paper, we prove that the $O(1/n)$ estimate for the error term ${\alpha }_n$ is, in general, best possible, by exhibiting an example for which \[ \liminf_{n\to\infty}\,nα_n>0. \] The proof makes use of the Faber polynomials, about which a conjecture is formulated.

arXiv comment7 pages