Fekete–Szegő conjecture for the class of q-starlike functions of order alpha

Let qq satisfy 0<q<10<q<1, let 0α<10\leq\alpha<1, and let fSq(α)f\in\mathcal{S}_q^*(\alpha) have the normalized expansion

f(z)=z+a2z2+a3z3+.f(z)=z+a_2z^2+a_3z^3+\cdots.

Let μ\mu be any complex number. Fekete–Szegő conjecture.

a3μa22max{2(12μ)(lnq1α(1q)q1)2+2(lnq1α(1q)q21),2(lnq1α(1q)q21)}.|a_3-\mu a_2^2|\leq \max\left\{\left|2(1-2\mu)\left(\frac{\ln \frac{q}{1-\alpha(1-q)}}{q-1}\right)^2+2\left(\frac{\ln \frac{q}{1-\alpha(1-q)}}{q^2-1}\right)\right|,2\left(\frac{\ln \frac{q}{1-\alpha(1-q)}}{q^2-1}\right)\right\}.

Equality occurs for the functions F1F_1 and F2F_2 given by

F1(z)=zexp[n=12lnq1α(1q)qn1zn]F_1(z)=z\exp\left[\sum_{n=1}^\infty \frac{2\ln \frac{q}{1-\alpha(1-q)}}{q^n-1}z^n\right]

and

F2(z)=zexp[n=12lnq1α(1q)q2n1z2n].F_2(z)=z\exp\left[\sum_{n=1}^\infty \frac{2\ln \frac{q}{1-\alpha(1-q)}}{q^{2n}-1}z^{2n}\right].

This is a Fekete–Szegő coefficient problem for the class Sq(α)\mathcal{S}_q^*(\alpha); the stated extremal functions are intended to show sharpness, but the source presents the result as a conjecture and gives no resolution evidence.

Sources & referencesView supporting material

Primary source

Sarita Agrawal, “Coefficient estimates for some classes of functions associated with \(q\)-function theory”, arXiv:1705.06957 (2017).

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