Inner factors of analytic functions of variable smoothness in the closed disk

St Petersburg Mathematical Journal. 2021. Vol. 32. P. 929–954.

Широков Н. А.

Let p⁡(ζ) be a positive function defined on the unit circle T and satisfying the condition|p⁡(ζ2)−p⁡(ζ1)|≤c0log⁡e|ζ2−ζ1|,ζ1,ζ2∈T,p−=minζ∈T⁡p⁡(ζ). Futhermore, let 0<α<1, r≥0, r∈Z, and assume that p−>1α. Define a class of analytic functions in the unit disk D as follows: f∈Hr+αp⁡(⋅) ifsup0<ρ<1⁡sup0<|θ|<π⁡∫02⁢π|f(r)⁡(ρ⁢ei⁢(λ+θ))−f(r)⁡(ρ⁢ei⁢λ)|θ|α|p(ei⁢λ)dλ<∞.The following main results are proved.

Theorem 1. Let f∈Hr+αp⁡(⋅), and let I be an inner function, f/I∈H1. Then f/I∈Hr+αp⁡(⋅).

Theorem 2. Let f∈Hr+αp⁡(⋅), and let I be an inner function, f/I∈H∞. Assume that the multiplicity of every zero of f in D is at least r+1. Then f⁢I∈Hr+αp⁡(⋅).

Ключевые слова: внутренняя функция, inner function, внешне-внутренняя факторизация Неванлинны, пространства Лебега переменной гладкости, Lebesgue spaces of variable smoothness