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Inclusion results for certain subclasses of p-valent meromorphic functions associated with a new operator

Abstract

In this paper, we introduce new subclasses of p-valent starlike, p-valent convex, p-valent close-to-convex, and p-valent quasi-convex meromorphic functions and investigate some inclusion properties of these subclasses and investigate various inclusion properties and integral-preserving properties for the p-valent meromorphic function classes.

MSC:30C45.

1 Introduction

Let Σ p denote the class of functions of the form

f(z)= z − p + ∑ k = 1 ∞ a k − p z k − p ( p ∈ N = { 1 , 2 , … } ) ,
(1.1)

which are analytic and p-valent in the punctured unit disc U ∗ ={z:z∈C and 0<|z|<1}. If f(z) and g(z) are analytic in U= U ∗ ∪{0}, we say that f(z) is subordinate to g(z), written f≺g or f(z)≺g(z) (z∈U), if there exists a Schwarz function w(z) in U with w(0)=0 and |w(z)|<1, such that f(z)=g(w(z)) (z∈U). Furthermore, if g(z) is univalent in U, then the following equivalence relationship holds true (see [3] and [8]):

f(z)≺g(z)⇔f(0)=g(0)andf(U)⊂g(U).

For functions f(z)∈ Σ p , given by (1.1) and g(z)∈ Σ p defined by

g(z)= z − p + ∑ k = 1 ∞ b k − p z k − p (p∈N),
(1.2)

the Hadamard product (or convolution) of f(z) and g(z) is given by

(f∗g)(z)= z − p + ∑ k = 1 ∞ a k − p b k − p z k − p =(g∗f)(z).
(1.3)

Aqlan et al.[1] defined the operator Q β , p α : Σ p → Σ p by:

Q β , p α f(z)={ z − p + Γ ( α + β ) Γ ( β ) ∑ k = 1 ∞ Γ ( k + β ) Γ ( k + β + α ) a k − p z k − p ( α > 0 ; β > − 1 ; p ∈ N ; f ∈ Σ p ) , f ( z ) ( α = 0 ; β > − 1 ; p ∈ N ; f ∈ Σ p ) .
(1.4)

Now, we define the operator H p , β , μ α : Σ p → Σ p as follows:

First, put

G β , p α (z)= z − p + Γ ( α + β ) Γ ( β ) ∑ k = 1 ∞ Γ ( k + β ) Γ ( k + β + α ) z k − p (p∈N)
(1.5)

and let G β , p , μ α ∗ be defined by

G β , p α (z)∗ G β , p , μ α ∗ (z)= 1 z p ( 1 − z ) μ (μ>0;p∈N).
(1.6)

Then

H p , β , μ α f(z)= G β , p α ∗ (z)∗f(z)(f∈ Σ p ).
(1.7)

Using (1.5)-(1.7), we have

H p , β , μ α f(z)= z − p + Γ ( β ) Γ ( α + β ) ∑ k = 1 ∞ Γ ( k + β + α ) ( μ ) k Γ ( k + β ) ( 1 ) k a k − p z k − p ,
(1.8)

where f∈ Σ p is in the form (1.1) and ( ν ) n denotes the Pochhammer symbol given by

( ν ) n = Γ ( ν + n ) Γ ( ν ) ={ 1 ( n = 0 ) , ν ( ν + 1 ) ⋯ ( ν + n − 1 ) ( n ∈ N ) .

It is readily verified from (1.8) that

z ( H p , β , μ α f ( z ) ) ′ =(α+β) H p , β , μ α + 1 f(z)−(α+β+p) H p , β , μ α f(z)
(1.9)

and

z ( H p , β , μ α f ( z ) ) ′ =μ H p , β , μ + 1 α f(z)−(μ+p) H p , β , μ α f(z).
(1.10)

It is noticed that, putting μ=1 in (1.8), we obtain the operator

H p , β , 1 α f(z)= z − p + Γ ( β ) Γ ( α + β ) ∑ k = 1 ∞ Γ ( k + α + β ) Γ ( k + β ) a k − p z k − p .
(1.11)

Let M be the class of analytic functions h(z) with h(0)=1, which are convex and univalent in U and satisfy Re{h(z)}>0 (z∈U).

For 0≤η, γ<p, we denote by Σ p S(η), Σ p K(η), Σ p C(η,γ), and Σ p C ∗ (η,γ), the subclasses of Σ p consisting of all p-valent meromorphic functions which are, respectively, starlike of order η, convex of order η, close-to-convex functions of order γ and type η, and quasi-convex functions of order γ and type η in U.

Making use of the principle of subordination between analytic functions, we introduce the subclasses Σ p S(η;ϕ), Σ p C(η;ϕ), Σ p K(η,γ;ϕ,ψ), and Σ p K ∗ (η,γ;ϕ,ψ) (0≤η, γ<p and ϕ,ψ∈M) of the class Σ p which are defined by:

and

From these definitions, we can obtain some well-known subclasses of Σ p by special choices of the functions ϕ and ψ as well as special choices of η, γ, and p (see [2, 5], and [10]).

Now, by using the linear operator H p , β , μ α (α≥0, μ>0, β>−1; p∈N) and for ϕ,ψ∈M, 0≤η, γ<p, we define new subclasses of meromorphic functions of Σ p by:

and

Σ p C β , μ α ∗ (η,γ;ϕ,ψ)= { f ∈ Σ p : H p , β , μ α f ∈ Σ p C ∗ ( η , γ ; ϕ , ψ ) } .

We also note that

f(z)∈ Σ p K β , μ α (η;ϕ)⇔− z f ′ ( z ) p ∈ Σ p S β , μ α (η;ϕ),
(1.12)

and

f(z)∈ Σ p C β , μ α ∗ (η,γ;ϕ,ψ)⇔− z f ′ ( z ) p ∈ Σ p C β , μ α (η,γ;ϕ,ψ).
(1.13)

In particular, we set

Σ p S β , μ α ( η ; 1 + A z 1 + B z ) = Σ p S β , μ α (η;A,B)(−1<B<A≤1)

and

Σ p K β , μ α ( η ; 1 + A z 1 + B z ) = Σ p K β , μ α (η;A,B)(−1<B<A≤1).

In this paper, we investigate several inclusion properties of the classes Σ p S β , μ α (η;ϕ), Σ p K β , μ α (η;ϕ), Σ p C β , μ α (η,γ;ϕ,ψ), and Σ p C β , μ α ∗ (η,γ;ϕ,ψ) associated with the operator H p , β , μ α . Some applications involving integral operators are also considered.

In order to establish our main results, we need the following lemmas.

Lemma 1[4]

Let Ï‚ and Ï… be complex constants and leth(z)be convex (univalent) in U withh(0)=1andRe{Ï‚h(z)+Ï…}>0. If

q(z)=1+ q 1 z+⋯
(1.14)

is analytic in U, then

q(z)+ z q ′ ( z ) ς q ( z ) + υ ≺h(z)(z∈U),

implies

q(z)≺h(z)(z∈U).

Lemma 2[7]

Leth(z)be convex (univalent) in U andψ(z)be analytic in U withRe{ψ(z)}≥0. If q is analytic in U andq(0)=h(0), then

q(z)+ψ(z)z q ′ (z)≺h(z)(z∈U)

implies

q(z)≺h(z)(z∈U).

2 Some inclusion results

In this section, we give some inclusion properties for meromorphic function classes, which are associated with the operator H p , β , μ α . Unless otherwise mentioned, we assume that α≥1, β>−1, μ>0, 0≤γ, η<p and p∈N.

Theorem 1 Forf(z)∈ Σ p , ϕ∈Mwith

max z ∈ U ( Re { ϕ ( z ) } ) < min z ∈ U [ p + μ − η p − η , α + β + p − η p − η ] ,

then we have

Σ p S β , μ + 1 α (η,ϕ)⊂ Σ p S β , μ α (η,ϕ)⊂ Σ p S β , μ α − 1 (η,ϕ).
(2.1)

Proof We will first show that

Σ p S β , μ + 1 α (η,ϕ)⊂ Σ p S β , μ α (η,ϕ).
(2.2)

Let f∈ Σ p S β , μ + 1 α (η;ϕ) and put

q(z)= 1 p − η ( − z ( H p , β , μ α f ( z ) ) ′ H p , β , μ α f ( z ) − η ) ,
(2.3)

where q(z) is analytic in U with q(0)=1. Applying (1.10) in (2.3), we have

−μ H p , β , μ + 1 α f ( z ) H p , β , μ α f ( z ) =(p−η)q(z)+η−(p+μ).
(2.4)

Differentiating (2.4) logarithmically with respect to z, we have

1 p − η ( − z ( H p , β , μ + 1 α f ( z ) ) ′ H p , β , μ + 1 α f ( z ) − η ) =q(z)+ z q ′ ( z ) ( p + μ ) − η − ( p − η ) q ( z ) (z∈U).
(2.5)

Since

max z ∈ U ( Re { ϕ ( z ) } ) < min z ∈ U p + μ − η p − η ,

we see that

Re { ( p + μ ) − η − ( p − η ) ϕ ( z ) } >0(z∈U).

Applying Lemma 1 to (2.5), it follows that q≺ϕ, that is, that f∈ Σ p S β , μ α (η;Ï•). The proof of the second part will follow by using arguments similar to those used in the first part with f∈ Σ p S β , μ α (η;Ï•) and using the identity (1.9) instead of (1.10). This completes the proof of Theorem 1. □

Theorem 2 Forf(z)∈ Σ p , ϕ∈Mwith

Proof Applying (1.10) and using Theorem 1, we have

f ( z ) ∈ Σ p K β , μ + 1 α ( η ; ϕ ) ⇔ H p , β , μ + 1 α f ( z ) ∈ Σ p K ( η ; ϕ ) ⇔ − z ( H p , β , μ + 1 α f ( z ) ) ′ p ∈ Σ p S ( η ; ϕ ) ⇔ H p , β , μ + 1 α ( − z f ′ ( z ) p ) ∈ Σ p S ( η ; ϕ ) ⇔ − z f ′ ( z ) p ∈ Σ p S β , μ + 1 α ( η ; ϕ ) ⇒ − z f ′ ( z ) p ∈ Σ p S β , μ α ( η ; ϕ ) ⇔ H p , β , μ α ( − z f ′ ( z ) p ) ∈ Σ p S ( η ; ϕ ) ⇔ − z ( H p , β , μ α f ( z ) ) ′ p ∈ Σ p S ( η ; ϕ ) ⇔ H p , β , μ α f ( z ) ∈ Σ p K ( η ; ϕ ) ⇔ f ( z ) ∈ Σ p K β , μ α ( η ; ϕ ) .

Also,

f ( z ) ∈ Σ p K β , μ α ( η ; ϕ ) ⇔ − z f ′ ( z ) p ∈ Σ p S β , μ α ( η ; ϕ ) ⇒ − z f ′ ( z ) p ∈ Σ p S β , μ α − 1 ( η ; ϕ ) ⇔ − z ( H p , β , μ α − 1 f ( z ) ) ′ p ∈ Σ p S ( η ; ϕ ) ⇔ H p , β , μ α − 1 f ( z ) ∈ Σ p K ( η ; ϕ ) ⇔ f ( z ) ∈ Σ p K β , μ α − 1 ( η ; ϕ ) .

This completes the proof of Theorem 2. □

Taking

ϕ(z)= 1 + A z 1 + B z (−1<B<A≤1;z∈U)

in Theorem 1 and Theorem 2, we have the following corollary.

Corollary 1 Let f(z)∈ Σ p and

1 + A 1 + B < min z ∈ U ( p + μ − η p − η , α + β + p − η p − η ) (−1<B<A≤1).

Then we have

Σ p S β , μ + 1 α (η;A,B)⊂ Σ p S β , μ α (η;A,B)⊂ Σ p S β , μ α − 1 (η;A,B)

and

Σ p K β , μ + 1 α (η;A,B)⊂ Σ p K β , μ α (η;A,B)⊂ Σ p K β , μ α − 1 (η;A,B).

Now, using Lemma 2, we obtain similar inclusion relations for the subclass Σ p C β , μ α (η;γ;ϕ,ψ).

Theorem 3 Let f(z)∈ Σ p and

max z ∈ U Re { ϕ ( z ) } < min z ∈ U ( p + μ − η p − η , α + β + p − η p − η ) .

Then we have

Proof First, we will prove that

Σ p C β , μ + 1 α (η;γ;ϕ,ψ)⊂ Σ p C β , μ α (η;γ;ϕ,ψ).

Let f∈ Σ p C β , μ + 1 α (η;γ;ϕ,ψ). Then, from the definition of the class Σ p C β , μ α (η;γ;ϕ,ψ), there exists a function g∈ Σ p S β , μ α (η;ϕ) such that

1 p − γ ( − z ( H p , β , μ + 1 α f ( z ) ) ′ H p , β , μ + 1 α g ( z ) − γ ) ≺ψ(z)(z∈U).
(2.6)

Now, let

q(z)= 1 p − γ ( − z ( H p , β , μ α f ( z ) ) ′ H p , β , μ α g ( z ) − γ ) ,
(2.7)

where q(z) is analytic in U with q(0)=1. Applying (1.10) in (2.6), we have

(2.8)

Since, by Theorem 1,

g(z)∈ Σ p S β , μ + 1 α (η;ϕ)⊂ Σ p S β , μ α (η;ϕ),

set

h(z)= 1 p − η ( − z ( H p , β , μ α g ( z ) ) ′ H p , β , μ α g ( z ) − η ) ,

where h≺ϕ in U, and ϕ∈M. Then, using (2.7) and (2.8), we have

H p , β , μ α ( − z f ′ ( z ) p ) = [ ( p − γ ) q ( z ) + γ ] H p , β , μ α g(z)
(2.9)

and

(2.10)

Differentiating both sides of (2.9) with respect to z and multiplying by z, we have

z ( H p , β , μ α ( − z f ′ ( z ) p ) ) ′ H p , β , μ α g ( z ) =(p−γ)z q ′ (z)− [ ( p − γ ) q ( z ) + γ ] [ ( p − η ) h ( z ) + η ] .
(2.11)

Making use of (2.6), (2.10), and (2.11), we have

1 p − γ ( − z ( H p , β , μ + 1 α f ( z ) ) ′ H p , β , μ + 1 α g ( z ) − γ ) =q(z)+ z q ′ ( z ) p + μ − η − ( p − η ) h ( z ) ≺ψ(z),z∈U.
(2.12)

Since h≺ϕ in U, and

max z ∈ U Re { h ( z ) } < p + μ − η p − η ,

then

Re { p + μ − η − ( p − η ) h ( z ) } >0(z∈U).
(2.13)

Hence, putting

χ(z)= 1 { p + μ − η − ( p − η ) h ( z ) } ,

in Eq. (2.12) and applying Lemma 2, we can show that q≺ψ, that is, that f∈ Σ p C β , μ α (η,γ;ϕ,ψ). The second part can be proved by using similar arguments and using (1.9). This completes the proof of Theorem 3. □

3 Inclusion properties involving the integral operator F p , δ

Now, we consider the generalized Libera integral operator F p , δ (f) (see [6] and [9]), defined by

F p , δ (f)(z)= δ z δ + p ∫ 0 z t δ + p − 1 f(t)dt= z − p + ∑ k = 1 ∞ δ δ + k a k − p z k − p (δ>−p).
(3.1)

From (3.1), we have

z ( H p , β , μ σ F p , δ ( f ) ( z ) ) ′ =δ H p , β , μ σ f(z)−(δ+p) H p , β , μ σ F p , δ (f)(z).
(3.2)

Theorem 4 Let ϕ∈M with

max z ∈ U ( Re { ϕ ( z ) } ) < δ + p − η p − η (δ>−p).

Iff∈ Σ p S β , μ α (η;ϕ), then F p , δ (f)∈ Σ p S β , μ α (η;ϕ).

Proof Let f∈ Σ p S β , μ α (η;ϕ) and put

h(z)= 1 p − η ( − z ( H p , β , μ σ F p , δ ( f ) ( z ) ) ′ H p , β , μ σ F p , δ ( f ) ( z ) − η ) ,
(3.3)

where h is analytic in U with h(0)=1. Then, by using (3.2) and (3.3), we have

−δ H p , β , μ σ f ( z ) H p , β , μ σ F p , δ ( f ) ( z ) =(p−η)h(z)+η−(p+δ).
(3.4)

Differentiating (3.4) logarithmically with respect to z, we have

1 p − η ( − z ( H p , β , μ σ f ( z ) ) ′ H p , β , μ σ f ( z ) − η ) =h(z)+ z h ′ ( z ) p + δ − η − ( p − η ) h ( z ) (z∈U).

Applying Lemma 1, we conclude that h≺ϕ(z∈U), which implies that F p , δ (f)∈ Σ p S β , μ α (η;ϕ). □

Theorem 5 Let ϕ∈M with

max z ∈ U ( Re { ϕ ( z ) } ) < δ + p − η p − η (δ>−p).

Iff∈ Σ p K β , μ α (η;ϕ), then F p , δ (f)∈ Σ p K β , μ α (η;ϕ).

Proof Applying Theorem 4 and (1.12), we have

f ( z ) ∈ Σ p K β , μ α ( η ; ϕ ) ⇔ − z f ′ ( z ) p ∈ Σ p S β , μ α ( η ; ϕ ) ⇒ F p , δ ( − z f ′ ( z ) p ) ( z ) ∈ Σ p S β , μ α ( η ; ϕ ) ⇔ − z p F p , δ ′ ( f ) ( z ) ∈ Σ p S β , μ α ( η ; ϕ ) ⇔ F p , δ ( f ) ( z ) ∈ K p , λ σ ( η ; ϕ ) .

This completes the proof of Theorem 5. □

From Theorem 4 and Theorem 5, we have the following corollary.

Corollary 2 Suppose that

1 + A 1 + B < δ + p − η p − η (δ>−p;−1<B<A≤1).

Then, for the classes Σ p S β , μ α (η;ϕ)and Σ p K β , μ α (η;ϕ), the following inclusion relations hold true:

f∈ Σ p S β , μ α (A,B)⇒ F p , δ (f)∈ Σ p S β , μ α (A,B)

and

f∈ Σ p K β , μ α (A,B)⇒ F p , δ (f)∈ Σ p K β , μ α (A,B).

Theorem 6 Let ϕ,ψ∈M with

max z ∈ U Re { ϕ ( z ) } < δ + p − η p − η (δ>−p).

Iff∈ Σ p C β , μ α (η,γ;ϕ,ψ), then F p , δ (f)∈ Σ p C β , μ α (η,γ;ϕ,ψ).

Proof Let f∈ Σ p C β , μ α (η,γ;ϕ,ψ). Then, from the definition of the class Σ p C β , μ α (η,γ;ϕ,ψ), there exists a function g∈ Σ p S β , μ α (η;ϕ) such that

1 p − γ ( − z ( H p , β , μ σ f ( z ) ) ′ H p , β , μ σ g ( z ) − γ ) ≺ψ(z)(z∈U).
(3.5)

Now, let

h(z)= 1 p − γ ( − z ( H p , β , μ σ F p , δ ( f ) ( z ) ) ′ H p , β , μ σ F p , δ ( g ) ( z ) − γ ) ,
(3.6)

where h(z) is analytic in U with h(0)=1. Applying (3.2) in (3.6), we have

(3.7)

Since g∈ Σ p S β , μ α (η;Ï•), then by Theorem 4, we have F p , δ (g)(z)∈ Σ p S β , μ α (η;Ï•). Let

q(z)= 1 p − η ( − z ( H p , β , μ σ F p , δ ( g ) ( z ) ) ′ H p , β , μ σ F p , δ g ( z ) − η ) ,
(3.8)

where q≺ϕ in U. Then, using the same techniques as in the proof of Theorem 3 and using (3.5) and (3.7), we have

1 p − γ ( − z ( H p , β , μ σ f ( z ) ) ′ H p , β , μ σ g ( z ) − γ ) =h(z)+ z h ′ ( z ) δ + p − η − ( p − η ) q ( z ) ≺ψ(z).
(3.9)

Since Re{ 1 δ + p − η − ( p − η ) q ( z ) }>0, then applying Lemma 2, we find that h≺ψ, which yields F p , δ (f)(z)∈ Σ p C β , μ α (η,γ;Ï•,ψ). This completes the proof of Theorem 6. □

Remark Putting μ=1 in the above results, we obtain the results corresponding to the operator H p , β , 1 α defined by (1.11).

Author’s contributions

The author read and approved the final manuscript.

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Mostafa, A. Inclusion results for certain subclasses of p-valent meromorphic functions associated with a new operator. J Inequal Appl 2012, 169 (2012). https://doi.org/10.1186/1029-242X-2012-169

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