Subordination by Certain Multivalent Functions Associated with Fractional Integral Operator ()
1. Introduction
Let
denote the class of analytic functions in the open unit disk
. For
and
, let
Let
and
be members of
. Then the function
is said to be subordinate to
, or
is said to be superordinate to
, written
or
, if there exists a function
, analytic in
such that
,
and
. We also observe that
in
if and only if
and
whenever
is univalent in
. Though there were several results on differential implications, a systematic study on this was started by Miller and Mocanu [1]. The first order differential subordination is defined as follows.
Definition 1.1. ([1]) Let
and let
be univalent in
. If
is analytic in
and satisfies the differential subordination
(1.1)
then
is called a solution of the differential subordination. The univalent function
is called a dominant of the solution of the differential subordination, or more simply a dominant if
for all
satisfying (1.1).
Moreover, we denote by
the class of function
that are analytic and injective on
, where
and are such that
for
.
We also denote
by the class of univalent functions
with
satisfying the following condition:
Then, we note that
is the class of convex (not necessarily normalized) function in
.
Let
denote the class of functions
of the form
(1.2)
which are analytic in the open unit disk
. Also, let
,
and
be complex numbers with
. Then the Gaussian/classical hypergeometric function
is defined by
(1.3)
where
is the Pochhammer symbol defined, in terms of the Gamma function, by
The hypergeometric function
is analytic in
and if
or
is a negative integer, then it reduces to a polynomial.
Various definition of operators of fractional calculus (that is, fractional integral and fractional derivative) are available in the literature (cf., e.g., [2]-[5]). We state here the following definition due to Saigo [6] (see also [7] [8]).
Definition 1.2. For
,
,
, the fractional integral operator
is defined by
where
is the Gaussian hypergeometric function defined by (1.3) and
is taken to be an analytic function in a simply-connected region of the
-plane containing the origin with the order
for
, and the multiplicity of
is removed by requiring that
to be real when
.
With the aid of the above definition, Owa et al. [8] defined a modification of the fractional integral operator
by
(1.4)
for
and
. Then it is observed that
also maps
onto itself as follows :
(1.5)
We note that
where
and
are the integral operators introduced by Choi et al. [9] and Liu [10].
It is easily verified from (1.5) that
(1.6)
The identity (1.5) plays an important and significant role in obtaining our results.
Making use of the principle of subordination, various subordination theorems involving certain integral operators for analytic functions in
were investigated Bulboacă [11] [12], Miller et al. [13] and Owa and Srivastava [14]. Recently, Kumar et al. [15] gave an unified approach to study the properties of all these linear operators by considering the aspect that these operators satify recurrence relation of some common forms. They studied properties of integral transforms in a similar way. Furthermore, the study of the subordination properties and their dual problems for various operators is a significant role in pure and applied mathematics. For some recent developments one may refer to [16]-[19].
In the present paper, we investigate the subordination results by certain multivalent functions associated with fractional integral operator
. Some interesting applications to the integral operator are also considered.
2. Subordination Results Involving Fractional Integral
Operator
In this section, we prove the subordination theorems involving the fractional
integral operator
defined by (1.4). The following results will be required in our investigation.
Lemma 2.1. ([20]) Let
with
and let
be analytic in
with
and
. If
is not subordinate to
, then there exist points
and
, for which
Lemma 2.2. ([1]) Let
be convex univalent in
and let
. Suppose that
and that
and
are analytic with
and satisfy
If
, with
satisfies
then
.
A function
defined on
is called the subordination chain (or Löwner chain)if
is analytic and univalent in
for all
,
is continuously differentiable on
for all
and
.
Lemma 2.3. ([21]) The function
with
Suppose that
is analytic in
for all
,
is continuously differentiable 0n
for all
. If
satisfies
and
for some positive constant
and
, then
is a subordination chain.
We begin by proving the following theorem.
Theorem 2.1. Let
and
. Also let
with
(2.1)
If the function
and
(2.2)
then
Proof. Let us define the function
by
(2.3)
A simple calculation using (1.6) and (2.3) gives
(2.4)
where
We note that the assumption (2.1) implies that
. Hence, combining (2.3) and (2.4), we have
(2.5)
Thus, from (2.5), we need to prove the following subordination implication:
(2.6)
For the particular case
, the implication (2.6) becomes
(2.7)
According to Lemma 2.2 for
and
and by applying the inequality (2.1), we deduce that the above implication (2.7) holds true.
Now we will show that our result for the case
. Without loss of generality, we can assume that
satisfies the conditions of Theorem 2.1 on the closed disk
and
. If not, then we replace
and
by
respectively, where
and then
is univalent on
. Since
where
, we would then prove that
and by letting
, we obtain
.
If we suppose that the implication (2.6) is not true, that is,
then, from Lemma 1, there exist point
and
such that
(2.8)
To prove the implication (2.6), we define the function
by
and we will prove that
is a subordination chain. At first, we note that
is analytic in
, for sufficient small
and for all
. We also have that
is continuously differentiable on
for each
. A simple computation show that
From the assumptions
and (2.1) with
, we deduce
(2.9)
Hence we have
and also we observe that
.
While, by a direct computation, we obtain
(2.10)
By applying the assumptions
and (2.1) to (2.10), we have
which completes the proof of the first condition of Lemma 2.3. Furthermore, we obtain
(2.11)
Since
, the function
may be written by
(2.12)
where
is a normalized univalent function in
. Moreover, for function
, we have the following sharp growth and distortion results [21]:
(2.13)
and
(2.14)
Hence, by using the equations (2.9), (2.12), (2.13) and (2.14) to (2.11), we can find easily an upper bound for the right-hand side of (2.12). Thus the function
satisfies the second condition of Lemma 2.3, which proves that
is a subordination chain. In particular, we note from the definition of subordination chain that
(2.15)
Making use of (2.5) and (2.8), we have
Then, according to (2.15), we deduce that
(2.16)
But the relation (2.16) contradicts the assumption (2.2), and hence we finally conclude that
. This evidently completes the proof of Theorem 2.1.
Taking
in Theorem 1, we get the following corollary:
Corollary 2.1. Let
and
and let
. If the function
and
then
Theorem 2.2. Let
and
. Also let
with
If the function
and
then
Proof. Let us define the function
as in the proof of Theorem 2.1 by
Then, by applying the equations (2.3) and (2.4), we have
The remaining part of the proof in Theorem 2.2 is much akin to that of Theorem 2.1 and so we omit the detailed proof.
Putting
in Theorem 2.2, we obtain the following result.
Corollary 2.2. Let
and
. Also let
with
If the function
and
then
For
and
, we consider the generalized Bernardi-Livera-Livingston operator
defined by (cf. [9] [22]-[24])
(2.17)
Now, we obtain the following subordination properties involving the integral operator defined by (2.17).
Theorem 2.3. Let
and
. Also let
with
where
is given by (2.17). If the function
and
then
Proof. From (2.17) we have
(2.18)
Let us define the function
by
(2.19)
A simple calculation using (2.18) and (2.19) gives
(2.20)
where
We also note that from the assumption,
. Hence, combining (2.19) and (2.20), we have
(2.21)
The remaining part of the proof is much akin to that of Theorem 2.1 and so we may omit for the proof involved.
Letting
and
in Theorem 2.3, we have the following Corollary.
Corollary 2.3. Let
and
. Also let
with
where
is given by (2.17). If the function
and
then
Theorem 2.4. Let
and
. Also let
with
where
is given by (2.17). If the function
and
then
The proof of Theorem 2.4 is similar to that of Theorem 2.2 and so the details may be omitted.
Putting
in Theorem 2.4, we obtain the following result.
Corollary 2.4. Let
and
. Also let
with
where
is given by (2.17). If the function
and
then
3. Conclusion
Fractional calculus is one of the most intensively developing areas of the mathematical analysis. The fractional calculus operators have gone deep across into the realm of the theory of univalent and multivalent functions. In this present paper, we have found some mapping properties of subordinations by certain multivalent functions in the open unit disk associated with fractional integral operator. Further research can be conducted based on this paper by using various operators of fractional calculus in geometric function theory.
Acknowledgements
This work was supported by Daegu National University of Education Research grant in 2024.