Hostname: page-component-8448b6f56d-dnltx Total loading time: 0 Render date: 2024-04-24T21:20:45.128Z Has data issue: false hasContentIssue false

Bohr–Rogosinski radius for a certain class of close-to-convex harmonic mappings

Published online by Cambridge University Press:  31 January 2023

Molla Basir Ahamed
Affiliation:
Department of Mathematics, Jadavpur University, Kolkata 700032, West Bengal, India e-mail: mbahamed.math@jadavpuruniversity.in
Vasudevarao Allu*
Affiliation:
Discipline of Mathematics, School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Bhubaneswar 752050, Odisha, India

Abstract

Let $ \mathcal {B} $ be the class of analytic functions $ f $ in the unit disk $ \mathbb {D}=\{z\in \mathbb {C} : |z|<1\} $ such that $ |f(z)|<1 $ for all $ z\in \mathbb {D} $. If $ f\in \mathcal {B} $ of the form $ f(z)=\sum _{n=0}^{\infty }a_nz^n $, then $ \sum _{n=0}^{\infty }|a_nz^n|\leq 1 $ for $ |z|=r\leq 1/3 $ and $ 1/3 $ cannot be improved. This inequality is called Bohr inequality and the quantity $ 1/3 $ is called Bohr radius. If $ f\in \mathcal {B} $ of the form $ f(z)=\sum _{n=0}^{\infty }a_nz^n $, then $ |\sum _{n=0}^{N}a_nz^n|<1\;\; \mbox {for}\;\; |z|<{1}/{2} $ and the radius $ 1/2 $ is the best possible for the class $ \mathcal {B} $. This inequality is called Bohr–Rogosinski inequality and the corresponding radius is called Bohr–Rogosinski radius. Let $ \mathcal {H} $ be the class of all complex-valued harmonic functions $ f=h+\bar {g} $ defined on the unit disk $ \mathbb {D} $, where $ h $ and $ g $ are analytic in $ \mathbb {D} $ with the normalization $ h(0)=h^{\prime }(0)-1=0 $ and $ g(0)=0 $. Let $ \mathcal {H}_0=\{f=h+\bar {g}\in \mathcal {H} : g^{\prime }(0)=0\}. $ For $ \alpha \geq 0 $ and $ 0\leq \beta <1 $, let

$$ \begin{align*} \mathcal{W}^{0}_{\mathcal{H}}(\alpha, \beta)=\{f=h+\overline{g}\in\mathcal{H}_{0} : \mathrm{Re}\left(h^{\prime}(z)+\alpha zh^{\prime\prime}(z)-\beta\right)>|g^{\prime}(z)+\alpha zg^{\prime\prime}(z)|,\;\; z\in\mathbb{D}\} \end{align*} $$

be a class of close-to-convex harmonic mappings in $ \mathbb {D} $. In this paper, we prove the sharp Bohr–Rogosinski radius for the class $ \mathcal {W}^{0}_{\mathcal {H}}(\alpha , \beta ) $.

Type
Article
Copyright
© The Author(s), 2023. Published by Cambridge University Press on behalf of The Canadian Mathematical Society

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Footnotes

V.A. is supported by SERB-CRG.

References

Abu Muhanna, Y., Bohr’s phenomenon in subordination and bounded harmonic classes . Complex Var. Elliptic Equ. 55(2010), 10711078.CrossRefGoogle Scholar
Abu Muhanna, Y., Ali, R. M., Ng, Z. C., and Hasni, S. F. M., Bohr radius for subordinating families of analytic functions and bounded harmonic mappings . J. Math. Anal. Appl. 420(2014), 124136.CrossRefGoogle Scholar
Ahamed, M. B., The Bohr–Rogosinski radius for a certain class of close-to-convex harmonic mappings . Comput. Methods Funct. Theory (2022). https://doi.org/10.1007/s40315-022-00444-6 CrossRefGoogle Scholar
Ahamed, M. B., The sharp refined Bohr–Rogosinski inequalities for certain classes of harmonic mappings . Complex Var. Elliptic Equ. (2022). https://doi.org/10.1080/17476933.2022.2155636 CrossRefGoogle Scholar
Ahamed, M. B., Allu, V., and Halder, H., Improved Bohr inequalities for certain class of harmonic univalent functions . Complex Var. Elliptic Equ. (2021). https://doi.org/10.1080/17476933.2021.1988583 Google Scholar
Ahamed, M. B., Allu, V., and Halder, H., Bohr radius for certain classes of close-to-convex harmonic mappings . Anal. Math. Phys. 11(2021), 111.CrossRefGoogle Scholar
Aizenberg, L., Remarks on the Bohr and Rogosinski phenomenon for power series . Anal. Math. Phys. 2(2012), 6978.CrossRefGoogle Scholar
Aizenberg, L., Elin, M., and Shoikhet, D., On the Rogosinski radius for holomorphic mappings and some of its applications . Studia Math. 168(2005), no. 2, 147158.CrossRefGoogle Scholar
Aizenberg, L., Gotliv, V., and Vidras, A., Bohr and Rogosinski abscissas for ordinary Dirichlet series . Comput. Method Funct. Theory 9(2009), no. 1, 6574.CrossRefGoogle Scholar
Aleman, A. and Constantin, A., Harmonic maps and ideal fluid flows . Arch. Ration. Mech. Anal. 204(2012), 479513.CrossRefGoogle Scholar
Alkhaleefah, S. A., Kayumov, I. R., and Ponnusamy, S., On the Bohr inequality with a fixed zero coefficient . Proc. Amer. Math. Soc. 147(2019), 52635274.CrossRefGoogle Scholar
Alkhaleefah, S. A., Kayumov, I. R., and Ponnusamy, S., Bohr–Rogosinski inequalities for bounded analytic functions . Lobachebiskii J. Math. 41(2021), no. 11, 21102119.CrossRefGoogle Scholar
Allu, V. and Halder, H., Bohr phenomenon for certain subclasses of harmonic mappings . Bull. Sci. Math. 173(2021), 103053.CrossRefGoogle Scholar
Allu, V. and Halder, H., Operator valued analogues of multidimensional Bohr’s inequality . Canad. Math. Bull. 65(2022), 10201035. https://doi.org/10.4153/S0008439521001077 CrossRefGoogle Scholar
Bénéteau, C., Dahlner, A., and Khavinson, D., Remarks on the Bohr phenomenon . Comput. Methods Funct. Theory 4(2004), 119.CrossRefGoogle Scholar
Boas, H. P. and Khavinson, D., Bohr’s power series theorem in several variables . Proc. Amer. Math. Soc. 125(1997), 29752979.CrossRefGoogle Scholar
Bohr, H., A theorem concerning power series . Proc. Lond. Math. Soc. s2qq-13(1914), 15.CrossRefGoogle Scholar
Chichra, P. N., New subclasses of the class of close-to-convex functions . Proc. Amer. Math. Soc. 62(1977), 3743.CrossRefGoogle Scholar
Constantin, O. and Martin, M. J., A harmonic maps approach to fluid flows . Math. Ann. 369(2017), 116.CrossRefGoogle Scholar
Das, N., Refinements of the Bohr and Rogosinski phenomena . J. Math. Anal. Appl. 508(2022), no. 1, 125847.CrossRefGoogle Scholar
Das, N., Estimates for generalized Bohr radii in one and higher dimensions . Canad. Math. Bull. (2022), 118. https://doi.org/10.4153/S0008439522000674 Google Scholar
Evdoridis, S., Ponnusamy, S., and Rasila, A., Improved Bohr’s inequality for locally univalent harmonic mappings . Indag. Math. (N.S.) 30(2019), no. 1, 201213.CrossRefGoogle Scholar
Gao, C.-Y. and Zhou, S.-Q., Certain subclass of starlike functions . Appl. Math. Comput. 187(2007), 176182.Google Scholar
Ghosh, N. and Allu, V., On a subclass of harmonic close-to-convex mappings . Monatsh. Math. 188(2019), 247267.CrossRefGoogle Scholar
Huang, Y., Liu, M.-S., and Ponnusamy, S., Refined Bohr-type inequalities with area measure for bounded analytic functions . Anal. Math. Phys. 10(2020), 50.CrossRefGoogle Scholar
Huang, Y., Liu, M.-S., and Ponnusamy, S., The Bohr-type operator on analytic functions and sections . Complex Var. Elliptic Equ. (2021). https://doi.org/10.1080/17476933.2021.1990272 Google Scholar
Huang, Y., Liu, M.-S., and Ponnusamy, S., Bohr-type inequalities for harmonic mappings with a multiple zero at the origin . Mediterr. J. Math. 18(2021), 75.CrossRefGoogle Scholar
Ismagilov, A., Kayumov, I. R., and Ponnusamy, S., Sharp Bohr type inequality . J. Math. Anal. Appl. 489(2020), 124147.CrossRefGoogle Scholar
Kayumov, I. R., Khammatova, D. M., and Ponnusamy, S., Bohr–Rogosinski phenomenon for analytic functions and Cesáro operators . J. Math. Anal. Appl. 496(2021), 124824.CrossRefGoogle Scholar
Kayumov, I. R. and Ponnusamy, S., Bohr’s inequalities for the analytic functions with lacunary series and harmonic functions . J. Math. Anal. Appl. 465(2018), 857871.CrossRefGoogle Scholar
Kayumov, I. R. and Ponnusamy, S., On a powered Bohr inequality . Ann. Acad. Sci. Fenn. Ser. A. 44(2019), 301310.Google Scholar
Kayumov, I. R. and Ponnusamy, S., Improved version of Bohr’s inequalities . C. R. Math. Acad. Sci. Paris 358(2020), no. 5, 615620.CrossRefGoogle Scholar
Kayumov, I. R. and Ponnusamy, S., Bohr–Rogosinski radius for analytic functions. Preprint, 2017. arXiv:1708.05585 Google Scholar
Kayumov, I. R., Ponnusamy, S., and Shakirov, N., Bohr radius for locally univalent harmonic mappings . Math. Nachr. 291(2018), 17571768.CrossRefGoogle Scholar
Kumar, S., A generalization of the Bohr inequality and its applications . Complex Var. Elliptic Equ. (2022). https://doi.org/10.1080/17476933.2022.2029853 Google Scholar
Li, L. and Ponnusamy, S., Injectivity of sections of univalent harmonic mappings . Nonlinear Anal. 89(2013), 276283.CrossRefGoogle Scholar
Lin, R., Liu, M., and Ponnusamy, S., The Bohr-type inequalities for holomorphic mappings with a Lacunary series in several complex variables . Acta Math. Sci. 43(2023), 6379. https://doi.org/10.1007/s10473-023-0105-8 CrossRefGoogle Scholar
Liu, G., Bohr-type inequality via proper combination . J. Math. Anal. Appl. 503(2021), no. 1, 125308.CrossRefGoogle Scholar
Liu, G., Liu, Z., and Ponnusamy, S., Refined Bohr inequality for bounded analytic functions . Bull. Sci. Math. 173(2021), 103054.CrossRefGoogle Scholar
Liu, M.-S. and Ponnusamy, S., Multidimensional analogues of refined Bohr’s inequality . Proc. Amer. Math. Soc. 149(2021), no. 5, 21332146.CrossRefGoogle Scholar
Liu, Z. and Ponnusamy, S., Bohr radius for subordination and k-quasiconformal harmonic mappings . Bull. Malays. Math. Sci. Soc. 42(2019), 21512168.CrossRefGoogle Scholar
Nagpal, S. and Ravinchandran, V., Construction of subclasses of univalent harmonic mappings . J. Korean Math. Soc. 51(2014), 567592.CrossRefGoogle Scholar
Paulsen, V. I. and Singh, D., Bohr’s inequality for uniform algebras . Proc. Amer. Math. Soc. 132(2004), 35773579.CrossRefGoogle Scholar
Ponnusamy, S., Vijayakumar, R., and Wirths, K.-J., New inequalities for the coefficients of unimodular bounded functions . RM 75(2020), 107.Google Scholar
Ponnusamy, S., Vijayakumar, R., and Wirths, K.-J., Improved Bohr’s phenomenon in quasi-subordination classes, J. Math. Anal. Appl. 506(2022), no. 1, 125645.CrossRefGoogle Scholar
Ponnusamy, S., Yamamoto, H., and Yanagihara, H., Variability regions for certain families of harmonic univalent mappings . Complex Var. Elliptic Equ. 58(2013), no. 1, 2334.CrossRefGoogle Scholar
Rajbala, and Prajapat, J. K., On a subclass of close-to-convex harmonic mappings . Asian-Eur. J. Math. https://doi.org/10.1142/s1793557121501023 Google Scholar
Rogosinski, W., Über Bildschranken bei Potenzreihen und ihren Abschnitten . Math. Z. 17(1923), 260276.CrossRefGoogle Scholar