Generalizations of Ahlfors lemma and boundary behavior of analytic functions
Date
2013-08-23
Authors
Arman, Andrii
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Abstract
In this thesis we will consider and investigate the properties of analytic
functions via their behavior near the boundary of the domain on which they are
defined. To do that we introduce the notion of the hyperbolic distortion and the hyperbolic
derivative. Classical results state that the hyperbolic derivative is
bounded from above by 1, and we will consider the case when it is
bounded from below by some positive constant.
Boundedness from below of the hyperbolic derivative implies
some nice properties of the function near the boundary. For instance Krauss & all in 2007 proved that, if the function is defined on a
domain bounded by analytic curve, then boundedness from below of the hyperbolic derivative implies that the
function has an analytic continuation across the boundary. We extend this result for the domains with slightly more general boundary, namely for smooth Jordan domains, and get that in this case the function and its derivative will have only continuous extensions to the boundary.
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Keywords
hyperbolic derivative, Ahlfors lemma, hyperbolic distortion, analytic continuation of a function, hyperbolic metric, Schwarz-Pick lemma, Jordan domains, Bloch space