A Small Intervals Theorem for Subharmonic Functions

Abstract

Let $\mathbb{C}$ be the complex plane, E be a measurable subset of a segment $[0, R]$ of the positive semiaxis $\mathbb{R}^+$, and $u\not\equiv - \infty$ be a subharmonic function on $\mathbb{C}$. The main result of this article is an upper estimate of the integral of the module $|u|$ over a subset of E through the maximum of the function u on a circle of radius R centered at zero and the linear Lebesgue measure of subset E. Our result develops one of the classical theorems of R. Nevanlinna, established in the case of $E=[0, R]$, and versions of so-called small arcs lemma by Edrei–Fuchs for small intervals on $\mathbb{R}^+$ from the works of A.F. Grishin, M.L. Sodin, and T.I. Malyutina. Our estimate is uniform in the sense that the constants in the inequality are absolute and do not depend on the subharmonic function u, under the semi-normalization $u(0)\geq 0$.