An extremal problem for the Bergman kernel of orthogonal polynomials

Abstract

Let $Γ\subset \mathbb C$ be a curve of class $C(2,α)$. For $z_{0}$ in the unbounded component of ${\mathbb C}\setminus Γ$, and for $n=1,2,...$, let $ν_n$ be a probability measure with supp$(ν_{n})\subset Γ$ which minimizes the Bergman function $B_{n}(ν,z):=\sum_{k=0}^{n}|q_{k}^ν(z)|^{2}$ at $z_{0}$ among all probability measures $ν$ on $Γ$ (here, $\{q_{0}^ν,\ldots,q_{n}^ν\}$ are an orthonormal basis in $L^2(ν)$ for the holomorphic polynomials of degree at most $n$). We show that $\{ν_{n}\}_n$ tends weak-* to $\hatδ_{z_{0}}$, the balayage of the point mass at $z_0$ onto $Γ$, by relating this to an optimization problem for probability measures on the unit circle. Our proof makes use of estimates for Faber polynomials associated to $Γ$.