On the leading coefficient of polynomials orthogonal over domains with corners

Erwin Miña-Díaz

Published 2014-07-18Version 1

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 \[ \frac{n+1}{\pi}\frac{\gamma^{2n+2}}{ \lambda_n^{2}}=1-\alpha_n, \] 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 \[ \liminf_{n\to\infty}\,n\alpha_n>0. \] The proof makes use of the Faber polynomials, about which a conjecture is formulated.