<p>In this paper, we study the class <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="36" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {A}(p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">A</mi> <mo stretchy="false">(</mo> <mi>p</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> which includes functions <i>f</i> that are meromorphic in the unit disk <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Delta \)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Δ</mi> </math></EquationSource> </InlineEquation> and have a simple pole at <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq3.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(z=p\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>z</mi> <mo>=</mo> <mi>p</mi> </mrow> </math></EquationSource> </InlineEquation> for some <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="68" /> </InlineMediaObject> <EquationSource Format="TEX">\(p\in (0,1)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mo>∈</mo> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> with the normalization <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="148" /> </InlineMediaObject> <EquationSource Format="TEX">\(f(0)=0=f'(0)-1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mn>0</mn> <mo>=</mo> <msup> <mi>f</mi> <mo>′</mo> </msup> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>. We establish a sufficient condition for functions in this class to be univalent. Making use of this condition, we introduce a subfamily of <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="36" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {A}(p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">A</mi> <mo stretchy="false">(</mo> <mi>p</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> consisting of univalent functions satisfying a certain differential inequality in <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Delta \)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Δ</mi> </math></EquationSource> </InlineEquation>. Next, we obtain a representation formula for such functions. Additionally, we establish necessary and sufficient conditions on the coefficients <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq8.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(b_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>b</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> for functions <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="68" /> </InlineMediaObject> <EquationSource Format="TEX">\(f\in \mathcal {A}(p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>∈</mo> <mi mathvariant="script">A</mi> <mo stretchy="false">(</mo> <mi>p</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> of the form <Equation ID="Equ9"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_Equ9.gif" Format="GIF" Height="37" Rendition="HTML" Resolution="72" Type="Linedraw" Width="273" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \frac{z}{f(z)}=1+b_1 z+b_2z^2+\cdots , \quad z\in \Delta , \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <mfrac> <mi>z</mi> <mrow> <mi>f</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> </mfrac> <mo>=</mo> <mn>1</mn> <mo>+</mo> <msub> <mi>b</mi> <mn>1</mn> </msub> <mi>z</mi> <mo>+</mo> <msub> <mi>b</mi> <mn>2</mn> </msub> <msup> <mi>z</mi> <mn>2</mn> </msup> <mo>+</mo> <mo>⋯</mo> <mo>,</mo> <mspace width="1em" /> <mi>z</mi> <mo>∈</mo> <mi mathvariant="normal">Δ</mi> <mo>,</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>to belong to this class. Furthermore, we determine sharp upper bounds for <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq10.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="30" /> </InlineMediaObject> <EquationSource Format="TEX">\(|b_n|\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">|</mo> </mrow> <msub> <mi>b</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">|</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for all <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_926_Article_IEq11.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(n\ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>. Finally, we establish a sharp estimate for the Fekete-Szegö functional associated with the newly introduced subclass.</p>

错误:搜索内容不能为空,请输入英文关键词
错误:关键词超出字数限制,请精简
高级检索

A class of meromorphic univalent functions characterized by a differential inequality

  • Kartika Verma,
  • S. Sunil Varma,
  • Firdoshi Parveen

摘要

In this paper, we study the class \(\mathcal {A}(p)\) A ( p ) which includes functions f that are meromorphic in the unit disk \(\Delta \) Δ and have a simple pole at \(z=p\) z = p for some \(p\in (0,1)\) p ( 0 , 1 ) with the normalization \(f(0)=0=f'(0)-1\) f ( 0 ) = 0 = f ( 0 ) - 1 . We establish a sufficient condition for functions in this class to be univalent. Making use of this condition, we introduce a subfamily of \(\mathcal {A}(p)\) A ( p ) consisting of univalent functions satisfying a certain differential inequality in \(\Delta \) Δ . Next, we obtain a representation formula for such functions. Additionally, we establish necessary and sufficient conditions on the coefficients \(b_n\) b n for functions \(f\in \mathcal {A}(p)\) f A ( p ) of the form \(\begin{aligned} \frac{z}{f(z)}=1+b_1 z+b_2z^2+\cdots , \quad z\in \Delta , \end{aligned}\) z f ( z ) = 1 + b 1 z + b 2 z 2 + , z Δ , to belong to this class. Furthermore, we determine sharp upper bounds for \(|b_n|\) | b n | for all \(n\ge 2\) n 2 . Finally, we establish a sharp estimate for the Fekete-Szegö functional associated with the newly introduced subclass.