Classes of Quasi-nearly Subharmonic Functions

Abstract

It is well known and important that if u ≥ 0 is subharmonic on a domain Ω in ℝn and p > 0, then there is a constant C(n,p) ≥ 1 such that \(u(x)^p\leq C(n,p){\mathcal{MV}}(u^p,B(x,r))\) for each open ball B(x,r) ⊂ Ω. The definition of a relatively new function class, quasi-nearly subharmonic functions, is based on such a generalized mean value inequality. It is pointed out that the obtained function class is natural. It has important and interesting properties and, at the same time, it is large: In addition to nonnegative subharmonic functions, it includes, among others, Herve’s nearly subharmonic functions, functions satisfying certain natural growth conditions, especially certain eigenfunctions, polyharmonic functions and generalizations of convex functions. Further, some of the basic properties of quasi-nearly subharmonic functions are stated in a unified form. Moreover, a characterization of quasi-nearly subharmonic functions with the aid of the quasihyperbolic metric and two weighted boundary limit results are given.