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Zap. Nauchn. Sem. POMI, 2011 Volume 389, Pages 21–33 (Mi znsl4116)

Extension of a theorem by Hardy and Littlewood

S. V. Bykov

I. G. Petrovsky Bryansk State University, Bryansk

Abstract: We give the following extension of a theorem by Hardy and Littlewood. Suppose $f$ is a holomorphic function in the unit disk and
$$ M_p(r,f)=\Bigl(\frac1{2\pi}\int_{-\pi}^\pi|f(re^{i\theta})|^pd\theta\Bigr)^{\frac1p}=O(\varphi(r)),\quad r\to1-0, $$
where $\varphi$ is a monotone increasing function on $(0,1)$ and
$$ \alpha_\varphi=\lim_{r\to1-0}\frac{\varphi'(r)(1-r)}{\varphi(r)}. $$

1) If $0\leq\alpha_\varphi<+\infty$, then $M_p(r,f')=O(\frac{\varphi(r)}{1-r})$, $r\to1-0$;
2) If $\alpha_\varphi=+\infty$, then $M_p(r,f')=O(\varphi'(r))$, $r\to1-0$.

Key words and phrases: holomorphic function, unit disk, Hardy–Littlewood theorem.

UDC: 517.53

Received: 24.06.2011


 English version:
Journal of Mathematical Sciences (New York), 2012, 182:5, 595–602

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© Steklov Math. Inst. of RAS, 2024