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On the generalized Zalcman conjecture. (English) Zbl 07931774

Summary: Let \(\mathcal{S}\) denote the class of analytic and univalent (i.e., one-to-one) functions \(f(z)= z+\sum_{n=2}^{\infty}a_n z^n\) in the unit disk \(\mathbb{D}=\{z\in \mathbb{C}:|z|<1\} \). For \(f\in \mathcal{S} \), In 1999, Ma proposed the generalized Zalcman conjecture that \[ |a_na_m-a_{n+m-1}| \le (n-1)(m-1), \quad \text{for } n\ge 2,\, m\ge 2, \] with equality only for the Koebe function \(k(z) = z/(1 - z)^2\) and its rotations. In the same paper, Ma (J Math Anal Appl 234:328-339, 1999) asked for what positive real values of \(\lambda\) does the following inequality hold? \[ |\lambda a_na_m-a_{n+m-1}| \le \lambda nm -n-m+1 \quad (n\ge 2, \,m\ge 3). \tag{0.1} \] Clearly equality holds for the Koebe function \(k(z) = z/(1 - z)^2\) and its rotations. In this paper, we prove the inequality (0.1) for \(\lambda =3\), \(n=2\), \(m=3\). Further, we provide a geometric condition on extremal function maximizing (0.1) for \(\lambda =2\), \(n=2\), \(m=3\).

MSC:

30C45 Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.)
30C50 Coefficient problems for univalent and multivalent functions of one complex variable
Full Text: DOI

References:

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