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On the Taylor coefficients of a subclass of meromorphic univalent functions

Complex Variables 2017-12-11 v1

Abstract

Let Vp(λ)\mathcal{V}_p(\lambda) be the collection of all functions ff defined in the unit disc \ID\ID having a simple pole at z=pz=p where 0<p<10<p<1 and analytic in \ID{p}\ID\setminus\{p\} with f(0)=0=f(0)1f(0)=0=f'(0)-1 and satisfying the differential inequality (z/f(z))2f(z)1<λ|(z/f(z))^2 f'(z)-1|< \lambda for z\IDz\in \ID, 0<λ10<\lambda\leq 1. Each fVp(λ)f\in\mathcal{V}_p(\lambda) has the following Taylor expansion: f(z)=z+n=2an(f)zn,z<p. f(z)=z+\sum_{n=2}^{\infty}a_n(f) z^n, \quad |z|<p. In \cite{BF-3}, we conjectured that an(f)1(λp2)npn1(1λp2)\mboxforn3. |a_n(f)|\leq \frac{1-(\lambda p^2)^n}{p^{n-1}(1-\lambda p^2)}\quad \mbox{for}\quad n\geq3. In the present article, we first obtain a representation formula for functions in the class Vp(λ)\mathcal{V}_p(\lambda). Using this representation, we prove the aforementioned conjecture for n=3,4,5n=3,4,5 whenever pp belongs to certain subintervals of (0,1)(0,1). Also we determine non sharp bounds for an(f),n3|a_n(f)|,\,n\geq 3 and for an+1(f)an(f)/p,n2|a_{n+1}(f)-a_n(f)/p|,\,n\geq 2.

Keywords

Cite

@article{arxiv.1712.02958,
  title  = {On the Taylor coefficients of a subclass of meromorphic univalent functions},
  author = {Bappaditya Bhowmik and Firdoshi Parveen},
  journal= {arXiv preprint arXiv:1712.02958},
  year   = {2017}
}

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8 pages