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Saminathan Ponnusamy

Publications and source records attributed to Saminathan Ponnusamy.

At least 19 recordsLinked to original sources
arXiv2026

Coefficients and Integral Mean Estimates for $K$-Quasiconformal Harmonic Mappings

Recently, Li and Ponnusamy~\cite{LiPonnusamy2025} established the coefficient conjecture proposed by Wang et al.~\cite{Wang2024} for several prominent geometric subclasses of $\mathcal{S}^0_H(K)$, the class of sense-preserving $K$-quasiconformal univalent harmonic mappings in the unit disk. In this paper, we show that the conjecture continues to hold for a class of $K$-quasiconformal harmonic mappings defined via quasi-subordination. Further, we determine the range of $p>0$ for which such mappings belong to the Hardy space ${\bf h}^p$ and the weighted Bergman space $\mathbf{a}^{\mathbf{p}}_{\boldsymbolβ}$, for $β>-1$. Our Hardy space result makes significant progress toward a problem posed by Pavlović, while the Bergman space result sharpens the range obtained by Das and Rasila~\cite{DasRasila}, doubling the previously known bounds. In addition, we obtain refined growth and integral mean estimates for the subclass, improving earlier results and providing further evidence toward an open problem raised by Das et al.~\cite{DasRasila2025}. Parallel results are also discussed for odd $K$-quasiconformal harmonic mappings.

math.CV↗
arXiv2026

On the Boundary Schwarz lemma and the rigidity theorem for certain mappings

In this article, we characterize the holomorphic mappings from $B_{\ell_p^n}\times\mathbb{D}^{m}$ into $\mathbb{D}^{m}$ for $p\in \{2,\infty\}$. In addition, we give a simple proof for the boundary Schwarz lemma for vector valued holomorphic functions, which also extends the existing result. Also, we obtain the boundary Schwarz lemma for pluriharmonic self-mappings of the unit ball $B_{\ell_p^n}$, $p \in [2,\infty]$. Furthermore, we establish the boundary rigidity theorem for holomorphic self-mappings of $B_{\ell_p^n}$, $p \in (1,\infty)$.

math.CV↗
arXiv2025

Asymptotic behavior of zeros of Bessel function derivatives

We derive two distinct asymptotic expansions for the zeros $j_{ν,k}^{(n)}$ of the $n$-th derivative of Bessel function $J_ν^{(n)}(x)$. The first is a McMahon-type expansion for the case when $k \to \infty$ with fixed $ν$, for which we also establish an explicit error bound. The second addresses the case when $ν\to \infty$ with fixed $k$ and it involves the zeros of Airy functions and their derivatives. These results extend and refine the classical work of Wong, Lang, and Olver on the zeros of Bessel functions. In the course of obtaining our main results, we also generalize several auxiliary results, which in turn provide a broader framework for the study of zeros of special functions.

math.CA↗
arXiv2025

On the coefficients estimate of K-quasiconformal harmonic mappings

Recently, the Wang et al. \cite{wwrq} proposed a coefficient conjecture for the family ${\mathcal S}_H^0(K)$ of $K$-quasiconformal harmonic mappings $f = h + \overline{g}$ that are sense-preserving and univalent, where $h(z)=z+\sum_{k=2}^{\infty}a_kz^k$ and $g(z)=\sum_{k=1}^{\infty}b_kz^k$ are analytic in the unit disk $|z|<1$, and the dilatation $ω=g'/h'$ satisfies the condition $|ω(z)| \leq k<1$ for $\ID$, with $K=\frac{1+k}{1-k}\geq 1$. The main aim of this article is provide an affirmative answer in support of this conjecture by proving this conjecture for every starlike function (resp. close-to-convex function) from $\mathcal{S}^0_H(K)$. In addition, we verify this conjecture also for typically real $K$-quasiconformal harmonic mappings. Also, we establish sharp coefficients estimate of convex $K$-quasiconformal harmonic mappings. By doing so, our work provides a document in support of the main conjecture of Wang et al..

math.CV↗
arXiv2025

On the dynamics of Halley's method

In this article, we study the global dynamics of Halley's method applied to complex polynomials. Specifically, we analyze the structure and connectivity of the Julia set of this method. The convergence behavior, symmetry properties, and topological features of the corresponding Fatou and Julia sets are studied for various classes of polynomials, including unicritical, cubic, and quartic polynomials with non-trivial symmetry groups. In particular, we prove that the Halley's method $H_p$ is convergent, its Julia set is connected, the immediate basins are unbounded and the symmetry group of it coincides with that of the polynomial whenever $p$ belongs to one of the above classes. We further extend our results to a broader class of polynomials. It is shown that the immediate basin of the Halley's method $H_p$ corresponding to a root of $p$ can be bounded. We also make some remarks on the dynamics of the Halley's method applied to a cubic polynomial in general.

math.DS↗
arXiv2024

Asymptotic value of the multidimensional Bohr radius

This article determines the exact asymptotic value of the Bohr radii and the arithmetic Bohr radii for the holomorphic functions defined on the unit ball of the $\ell_p^n$ space and having values in the simply connected domain of $\mathbb{C}$. Moreover, we investigate sharp Bohr radius for four distinct categories of holomorphic functions. These functions map the bounded balanced domain $G$ of a complex Banach space $X$ into the following domains: the right half-plane, the slit domain, the punctured unit disk, and the exterior of the closed unit disk.

math.CV↗
arXiv2024

Multidimensional analogues of the refined versions of Bohr inequalities involving Schwarz mappings

Our first aim of this article is to establish several new versions of refined Bohr inequalities for bounded analytic functions in the unit disk involving Schwarz functions. Secondly, %as applications of these results, we obtain several new multidimensional analogues of the refined Bohr inequalities for bounded holomorphic mappings on the unit ball in a complex Banach space involving higher dimensional Schwarz mappings. All the results are proved to be sharp.

math.CV↗
arXiv2023

Busemann functions and uniformization of Gromov hyperbolic spaces

Uniformization theory of Gromov hypebolic spaces investigated by Bonk, Heinonen and Koskela, generalizes the case where a classical Poincaré ball type model is used as the starting point. In this paper, we develop this approach in the case where the underlying domain is unbounded, corresponding to the classical Poincaré half-space model. More precisely, we study conformal densities via Busemann functions on Gromov hyperbolic spaces and prove that the deformed spaces are unbounded uniform spaces. Furthermore, we show that there is a one-to-one correspondence between the bilipschitz classes of proper geodesic Gromov hyperbolic spaces that are roughly starlike with respect to a point on Gromov boundary and the quasisimilarity classes of unbounded locally compact uniform spaces. Our result can be understood as an unbounded counterpart of the main result of Bonk, Heinonen, and Koskela in "Uniformizing Gromov Hyperbolic Spaces", Astérisque 270 (2001).

math.CV↗
arXiv2023

Stable classes of harmonic mappings

Let $\mathcal{H}_0$ denote the set of all sense-preserving harmonic mappings $f=h+\overline{g}$ in the unit disk $\ID$, normalized with $h(0)=g(0)=g'(0)=0$ and $h'(0)=1$. In this paper, we investigate some properties of certain subclasses of $\mathcal{H}_0$, including inclusion relations and stability analysis by precise examples, coefficient bounds, growth, covering and distortion theorems. As applications, we build some Bohr inequalities for these subclasses by means of subordination. Among these subclasses, six classes consist of functions $f=h+\overline{g}\in\mathcal{H}_0$ such that $h+εg$ is univalent (or convex) in $\D$ for each $|ε|=1$ (or for some $|ε|=1$, or for some $|ε|\leq1$). Simple analysis shows that if the function $f=h+\overline{g}$ belongs to a given class from these six classes, then the functions $h+\overline{εg}$ belong to corresponding class for all $|ε|=1$. We call these classes as stable classes.

math.CV↗
arXiv2023

Landau-type theorems for certain bounded bi-analytic functions and biharmonic mappings

In this paper, we establish three new versions of Landau-type theorems for bounded bi-analytic functions of the form $F(z)=\bar{z}G(z)+H(z)$, where $G$ and $H$ are analytic in the unit disk $|z|<1$ with $G(0)=H(0)=0$ and $H'(0)=1$. In particular, two of them are sharp while the other one either generalizes or improves the corresponding result of Abdulhadi and Hajj. As consequences, several new sharp versions of Landau-type theorems for certain subclasses of bounded biharmonic mappings are proved.

math.CV↗
arXiv2023

Bohr-type inequalities for unimodular bounded analytic functions

In this paper, we establish several new versions of Bohr-type inequalities for bounded analytic functions in the unit disk by allowing $φ=\{φ_n(r)\}^{\infty}_{n=0}$ in place of the $\{r^n\}^{\infty}_{n=0}$ in the power series representations of the functions involved with the Bohr sum and thereby introducing a single parameter, which generalize several related results of earlier authors.

math.CV↗
arXiv2023

On Schwarz-Pick type inequality and Lipschitz continuity for solutions to nonhomogeneous biharmonic equations

The purpose of this paper is to study the Schwarz-Pick type inequality and the Lipschitz continuity for the solutions to the nonhomogeneous biharmonic equation: $Δ(Δf)=g$, where $g:$ $\overline{\ID}\rightarrow\mathbb{C}$ is a continuous function and $\overline{\ID}$ denotes the closure of the unit disk $\ID$ in the complex plane $\mathbb{C}$. In fact, we establish the following properties for these solutions: Firstly, we show that the solutions $f$ do not always satisfy the Schwarz-Pick type inequality $$\frac{1-|z|^2}{1-|f(z)|^2}\leq C, $$ where $C$ is a constant. Secondly, we establish a general Schwarz-Pick type inequality of $f$ under certain conditions. Thirdly, we discuss the Lipschitz continuity of $f$, and as applications, we get the Lipschitz continuity with respect to the distance ratio metric and the Lipschitz continuity with respect to the hyperbolic metric.

math.CV↗
arXiv2022

An elementary counterexample to a coefficient conjecture

In this article, we consider the family of functions $f$ meromorphic in the unit disk $\ID=\{z :\,|z| < 1\}$ with a pole at the point $z=p$, a Taylor expansion \[f(z)= z+\sum_{k=2}^{\infty} a_kz^k, \quad |z|<p, \] and satisfying the condition \[\left |\left(\frac{z}{f(z)}\right)-z\left(\frac{z}{f(z)}\right)'-1\right |<λ,\, \forall z\in\ID, \] for some $λ$, $0<λ< 1$. We denote this class by $\mathcal{U}_m(λ)$ and we shall prove a representation theorem for the functions in this class. As consequences, we get a simple proof for the estimates of $|a_2|$ and obtain inequalities for the initial coefficients of the Laurent series of $f\in \mathcal{U}_m(λ)$ at its pole. In \cite{PW2} it had been conjectured that for $f\in \mathcal{U}_m(λ)$ the inequalities \[|a_n|\,\leq\,\frac{1}{p^{n-1}}\sum_{k=0}^{n-1}(λp^2)^k, \quad n\geq 2 \] are valid. We provide a counterexample to this conjecture for the case $n=3$.

math.CV↗
arXiv2022

Schwarz type lemmas and their applications in Banach spaces

The main purpose of this paper is to develop some methods to investigate the Schwarz type lemmas of holomorphic mappings and pluriharmonic mappings in Banach spaces. Initially, we extend the classical Schwarz lemmas of holomorphic mappings to Banach spaces, and then we apply these extensions to establish a sharp Bloch type theorem for pluriharmonic mappings on homogeneous unit balls of $\C^n$ and to obtain some sharp boundary Schwarz type lemmas for holomorphic mappings in Banach spaces. Furthermore, we improve and generalize the classical Schwarz lemmas of planar harmonic mappings into the sharp forms of Banach spaces, and present some applications to sharp boundary Schwarz type lemmas for pluriharmonic mappings in Banach spaces. Additionally, using a relatively simple method of proof, we prove some sharp Schwarz-Pick type estimates of pluriharmonic mappings in JB$^*$-triples, and the obtained results provide the improvements and generalizations of the corresponding results in \cite{CH20}.

math.CV↗
arXiv2022

Gromov hyperbolicity in the free quasiworld. I

With the aid of a Gromov hyperbolic characterization of uniform domains, we first give an affirmative answer to an open question arisen by Väisälä under weaker assumption. Next, we show that the three-point condition introduced by Väisälä is necessary to obtain quasisymmetry for quasimöbius maps between bounded connected spaces in a quantitative way. Based on these two results, we investigate the boundary behavior of freely quasiconformal and quasihyperbolic mappings on uniform domains of Banach spaces and partially answer another question raised by Väisälä in different ways.

math.CV↗
arXiv2022

Bloch and Landau type theorems for pluriharmonic mappings

In this paper, we establish two new versions of Landau-type theorems for pluriharmonic mappings with a bounded distortion. Then using these results, we derive three Bloch-type theorems of pluriharmonic mappings, which improve the corresponding results of Chen and Gauthier.

math.CV↗