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On the number of zeros of certain rational harmonic functions
Authors:Dmitry Khavinson   Genevra Neumann
Affiliation:Department of Mathematical Sciences, University of Arkansas, Fayetteville, Arkansas 72701 ; Department of Mathematics, Kansas State University, Manhattan, Kansas 66506
Abstract:
Extending a result of Khavinson and Swiatek (2003) we show that the rational harmonic function $overline{r(z)} - z$, where $r(z)$ is a rational function of degree $n > 1$, has no more than $5n - 5$ complex zeros. Applications to gravitational lensing are discussed. In particular, this result settles a conjecture by Rhie concerning the maximum number of lensed images due to an $n$-point gravitational lens.

Keywords:Rational harmonic mappings   fixed points   argument principle   gravitational lenses
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