文摘
We establish universality limits for measures on a subarc of the unit circle. Assume that $\mu $ is a regular measure on such an arc, in the sense of Stahl, Totik, and Ullmann, and is absolutely continuous in an open arc containing some point $z_{0}={\text{ e }}^{i\theta _{0}}$ . Assume, moreover, that $\mu ^{\prime }$ is positive and continuous at $z_{0}$ . Then universality for $\mu $ holds at $z_{0}$ , in the sense that the reproducing kernel $K_{n}\left( z,t\right) $ for $\mu $ satisfies $$\begin{aligned} \lim _{n\rightarrow \infty }\frac{K_{n}\left( z_{0}\exp \left( \frac{2\pi is}{ n}\right) ,z_{0}\exp \left( \frac{2\pi i\bar{t}}{n}\right) \right) }{ K_{n}\left( z_{0},z_{0}\right) }={\text{ e }}^{i\pi \left( s-t\right) }S\left( \left( s-t\right) T\left( \theta _{0}\right) \right) , \end{aligned}$$ uniformly for $s,t$ in compact subsets of the plane, where $S\left( z\right) =\frac{\sin \pi z}{\pi z}$ is the sinc kernel, and $T/2\pi $ is the equilibrium density for the arc.