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Construction of a certain superharmonic majorant

Paul Koosis (1994)

Annales de l'institut Fourier

Given a function f ( t ) 0 on with - ( f ( t ) / ( 1 + t 2 ) ) d t < and | f ( t ) - f ( t ' ) | l | t - t ' | , a procedure is exhibited for obtaining on a (finite) superharmonic majorant of the function F ( z ) : 1 π - | 𝔍 z | | z - t | 2 f ( t ) d t - A l | 𝔍 z | , where A is a certain (large) absolute constant. This leads to fairly constructive proofs of the two main multiplier theorems of Beurling and Malliavin. The principal tool used is a version of the following lemma going back almost surely to Beurling: suppose that f ( t ) , positive and bounded away from 0 on , is such that - ( f ( t ) / ( 1 + t 2 ) d t < and denote, for any constant α > 0 and each x , the unique...

Convolutions of harmonic right half-plane mappings

YingChun Li, ZhiHong Liu (2016)

Open Mathematics

We first prove that the convolution of a normalized right half-plane mapping with another subclass of normalized right half-plane mappings with the dilatation [...] −z(a+z)/(1+az) - z ( a + z ) / ( 1 + a z ) is CHD (convex in the horizontal direction) provided [...] a=1 a = 1 or [...] −1≤a≤0 - 1 a 0 . Secondly, we give a simply method to prove the convolution of two special subclasses of harmonic univalent mappings in the right half-plane is CHD which was proved by Kumar et al. [1, Theorem 2.2]. In addition, we derive the convolution...

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