English

On the failure of Bombieri's conjecture for univalent functions

Complex Variables 2017-10-24 v5

Abstract

A conjecture of Bombieri states that the coefficients of a normalized univalent function ff should satisfy lim inffKnReanmReam=mintRnsintsin(nt)msintsin(mt), \liminf_{f\to K} \frac{n-{\rm Re\,}a_n}{m-{\rm Re\,}a_m} = \min_{t\in{\mathbb R}} \, \frac{n\sin t -\sin(nt)}{m\sin t -\sin(mt)}, when ff approaches the Koebe function K(z)=z(1z)2K(z)=\frac{z}{(1-z)^2}. Recently, Leung disproved this conjecture for n=2n=2 and for all m3m\geq3 and, also, for n=3n=3 and for all odd m5m\geq5. Complementing his work we disprove it for all m>n2m>n\geq2 which are simultaneously odd or even and, also, for the case when mm is odd, nn is even and nm+12n\leq \frac{m+1}{2}. We mostly make use of trigonometry, but also employ Dieudonn\'e's criterion for the univalence of polynomials.

Keywords

Cite

@article{arxiv.1612.07242,
  title  = {On the failure of Bombieri's conjecture for univalent functions},
  author = {Iason Efraimidis},
  journal= {arXiv preprint arXiv:1612.07242},
  year   = {2017}
}

Comments

10 pages, LaTeX; a reference and an appendix were added in versions v2 and v3; in version v4 an additional reference was included as well as comments on alternative ways of proving Lemma 3 and making the last step in the proof of Theorem 1; to appear in Comput. Methods Funct. Theory