Abstract
We address weighted composition operators from -Bloch spaces to Bers-type spaces of bounded holomorphic functions on Y, where Y is a generalized Hua domain of the first kind, and obtain some necessary and sufficient conditions for the boundedness and compactness of those operators.
Keywords:
generalized Hua domain of the first type; α-Bloch space; Bers-type space; weighted composition operators; boundedness and compactness MSC:
32A27; 47B33
1. Introduction
Let be a bounded domain of and the class of all holomorphic functions on . Then, consider a holomorphic self-map of and a function . The linear operator
is referred to as a weighted composition operator for . If , it reduces to the composition operator, whereas for , it becomes the multiplication operator. For any given holomorphic function f, represents a generalized composition/multiplication operator. The reader is referred to book [1] for an extensive introduction to the topic.
In this paper, we study the boundedness and the compactness of weighted composition operators from -Bloch spaces to Bers-type spaces built on generalized Hua domains of the first kind. On the -Bloch space consists of all , such that
where
It is clear that is a Banach space.
In 1930, Cartan [2] was the the first to characterize the six types of irreducible bounded symmetric domains, which consist of four types of bounded symmetric classical domains, also referred to as Cartan domains, and two exceptional domains, whose complex dimension are 16 and 27, respectively. The Cartan domains are defined as follows:
where denotes the transpose of Z, denotes the conjugate of Z, and are positive integers. In 1998, building on the notion of bounded symmetric domains, Yin and Roos constructed a new type of domain called the Cartan–Hartogs domain [3], and Yin introduced the so-called Hua domains [4], which include the Cartan–Hartogs domains, the Cartan–Egg domains, the Hua domains, the generalized Hua domains, and the Hua construction. The generalized Hua domains are defined as follows:
where , denote, respectively, the Cartan domains of the first type, second type, third type, and fourth type, denotes the transpose of Z, denotes the conjugate of Z, are positive integers, and are positive real numbers. For , the generalized Hua domain of the first kind reduces to the unit ball. Without loss of generality, we may assume that , then and . We define
We also write
where
For the sake of convenience, the four types of generalized Hua domains will be referred to as , and .
On , a Bers-type space consists of all , such that
It is easy to see that is a Banach space with norm .
The boundedness and the compactness of weighted composition operators on (or between) spaces of holomorphic functions on various domains have received considerable attention. Wang and Liu [5] studied the boundedness and the compactness of the weighted composition operators on the Bers-type space on the open unit disc, whereas Zhou and Xu [6] characterized the boundedness and the compactness of the weighted composition operators between -Bloch space and -Bloch space, Li [7] investigated the boundedness and the compactness of the weighted composition operators from Hardy space to Bers-type space, and Zhu [8] characterized the boundedness and compactness of . For the unit poly-disk, Li and Stević [9,10] presented some necessary and sufficient conditions for the boundedness and the compactness of the weighted composition operators between and -Bloch space, whereas for the open unit ball, Li and Stević [11] studied the boundedness and the compactness of the weighted composition operators between and Bloch space (see also [12,13,14,15]).
The boundness and compactness of weighted composition have wide applications in differential equations, functional analysis, numerical mathematics, and control theory. For example, in differential equations, the compactness of the operator plays a vital role in proving the global existence of weak/strong solutions of fluid mechanics, see for example, the well-known Aubin–Lions argument [16]; in functional analysis, the compactness of the operator is crucial for the existence of critical points in studying the existence and multiplicity of periodic solutions of nonlinear Dirac equations [17]; in numerical mathematics, the boundness and compactness of the operator are applied in an implicit robust numerical scheme with graded meshes for the modified Burgers model with nonlocal dynamic properties [18], a space-time spectral order sinc-collocation method for the fourth-order nonlocal heat model arising in viscoelasticity [19], and a high-order and efficient numerical technique for the nonlocal neutron diffusion equation representing neutron transport in a nuclear reactor [20].
Jiang [21] has characterized the boundedness and the compactness of the weighted composition operators on the Bers-type space on the Hua domains. Yet, the boundedness and the compactness of the weighted composition operators from -Bloch to have not been studied in detail. In this paper, we obtain some necessary and sufficient conditions for the boundedness and the compactness of the weighted composition operators from -Bloch to on generalized Hua domain of the first kind by using a generalization of Hua’s inequalities.
2. Preliminaries
Lemma 1.
Let , then
for all and .
Proof.
By the very definition of Bers-type space , we know that
and so,
□
Lemma 2.
Let , and , with q as a positive integer, then
Proof.
□
Lemma 3
(see [22]). Let , if , then
if or , then
and “=” holds if and only if or .
Lemma 4
(see [22]). Let , then
where the equality holds if and only if .
Lemma 5
(see [22]). Let , if , then
If , then
where the equality holds if and only if , then . If , the equality always holds. If , then at most one of the is not zero.
Lemma 6
(see [23]). Let
be an matrix . Then, there exists an unitary matrix U and an unitary matrix V, such that
and
where are the characteristic values of . .
Lemma 7
(see [23]). Let
satisfying
Then, there exists a square matrix P, such that
and the minimum value is obtained for and , where
Lemma 8
(see [22], the Minkowski inequality of integration formula). Let , then
where the equal sign holds if and only if , .
Lemma 9.
Let be positive integers, , and , then
for .
Proof.
Decomposition in polar coordinates gives
Given , we may consider the function
Upon differentiating with respect to t, we obtain
An application of (6) then gives
This shows that is a concave function. It follows that
is a convex function, and we have
The very definition of shows that
□
Lemma 10.
Let us consider , some positive intergers , , . Then, the following inequality holds
where .
Lemma 11.
Given , some positive integers , , , and f a holomorphic function on , then there exists a constant C, such that
where .
Proof.
According to Lemmas 2 and 9 and (13),
where .
Case 1: ,
where .
Case 2: ,
where .
Case 3: ,
where ,
Lemma 12.
Let be a holomorphic self-map of and . The weighted composition operator is compact if and only if is bounded and for any bounded sequence in converging to 0 uniformly on compact subsets of , as .
Proof.
Assume that is compact. Let be a bounded sequence in and uniformly on compact subsets of as .
If as , then there exists a subsequence of , such that
Since is compact, there exists a subsequence of the bounded sequence (without loss of generality, we still write ), such that
Let K be a compact subspace of . From Lemma 1, it follows that
for Thus, uniformly on K. This means that for arbitrary , such that for , we have
for all . Since on compact subsets of as , there also exists a positive integer , for whenever . Let and , whenever , we have
From the arbitrariness of , we obtain , . By the uniqueness theorem of analytic functions, we have . This shows that , which contradicts the assumption .
Conversely, suppose that is a bounded sequence in , then for all n. Clearly is uniformly bounded on compact subsets of . By Montel’s theorem, there exists a subsequence of , such that uniformly on every compact subset of and . For all , there exists a compact set , such that . By Weierstrass’ theorem and because as , for , we obtain as . Then, there exists a , such that for , we have for . In addition, , which suffices to obtain
For all , . We thus have and and on every compact subset of as . Consequently, we have
which shows that is compact. □
Lemma 13.
Let , if , then
and “=” holds if and only if . If , then
Proof.
For , since , there exists two unitary matrices and two unitary matrices (by Lemma 6), such that
Then, one has
By Lemma 7, there exists a square matrix P, such that
where is a permutation of .
If , and using (7) and Lemma 8, we obtain
If , by using (6) and Lemma 8, we obtain
For , there exists a unitary matrix , such that
According to (20), we have
Thus, the inequality
holds when , whereas the equal sign holds if and only if .
According to (21), we see that
Thus, the inequality
holds when , with the equality holding if and only if and . □
Lemma 14.
Assume and , then
with equality that holds if and only if .
Lemma 15.
Assume and , then
Proof.
By the elementary inequality and Lemma 14, we have
□
Lemma 16
(see [24]). Assume , then there exists a constant C, such that
where is an matrix, where the elements of the gth row and lth column are one and the other elements are zero.
3. Boundedness of
Theorem 1.
Assume that , , and that () are positive integers. Let be a holomorphic self-map of , with and . If
Then, the weighted composition operator is bounded.
Conversely, if the weighted composition operator is bounded, then
Proof.
Assume that (27) holds. By Lemma 11 and for , we know that
For all , we have
which implies that is bounded.
Conversely, assume that is bounded. For any , let us introduce a test function , such that
This means that
In view of (18), it follows that
Then,
which means that
According to (29) and Lemmas 14 and 16, there exists a constant , such that
Since , one has
Therefore, we have
Let us now consider
so that
The proof is thus completed. □
Theorem 2.
Assume that , , and that are positive integers . Let be a holomorphic self-map of , with and . If
then, the weighted composition operator is bounded.
Conversely, if the weighted composition operator is bounded, then,
Proof.
Assume that (30) holds. By Lemma 11 and for , we have
For all , we obtain
This implies that is bounded.
Conversely, assume that is bounded. For , define a test function , such that
For the test function f, we have
From (29) and Lemmas 14 and 16, there exists a constant , such that
Since , we obtain
It follows that
We write , then
This completes the proof of the theorem. □
Corollary 1.
For , we have the case of the unit ball and is bounded if and only if
when . This result is equivalent to that obtained by Li and Stević in [11].
4. Compactness of
Theorem 3.
Assume that , , and that are positive integers. Let be a holomorphic self-map of , with and . If and
then the weighted composition operator is compact.
Conversely, if the weighted composition operator is compact, then and
Proof.
Assume that (32) holds. We have
If is bounded, consider the bounded sequence in , which converges to 0 uniformly on compact subsets of . Hence, there exists , such that . By (32), this means that , , such that for , we have
According to Lemma 11, we obtain
On the other hand, let us introduce the set
which is a compact subset of . By the assumptions, converges to 0 uniformly on any compact subset of . From this, and since , for such , we have
Consequently, making use of Lemma 12, we finally have that is compact.
Conversely, suppose is compact. Let , we have
This shows that Consider now a sequence in , such that as . If such a sequence does not exist, then condition (33) obviously holds. Moreover, let us introduce the following sequence of test functions :
Differentiation gives
From (29) and Lemmas 14 and 16, there exists a constant , such that
We now have two cases.
Case A. If , then
where .
Case A. If , then
Since , we may write with
Using (39), we have and
Hence,
By using both cases and , we have and then , which means that is bounded, where It follows that and
If , then
Since , we take and obtain . This implies , then . Let us now consider a compact subset E of . For , it is easy to see that has a positive lower bound. Thus, we have on all compact subsets of . If , then
From and as , one concludes that .
The above proof shows that on all compact subsets of . By Lemma 12, this implies that . Therefore, we conclude that
□
Theorem 4.
Assume that , , and that are some positive integers . Let be a holomorphic self-map of , with and . If and
then the weighted composition operator is compact.
Conversely, if the weighted composition operator is compact, then and
Proof.
Assume that (40) holds. We have
From Theorem 2, it follows that is bounded. Let be a bounded sequence in with that converges to 0 uniformly on compact subsets of . There exists , such that . By (40), for any , there is a constant , such that
for . Using Lemma 11, we have
On the other hand, if we set
we have that is a compact subset of . For defined in (42), converges to 0 uniformly on any compact subset of . For , we have
Consequently, making use of Lemma 12, we have that is compact.
Conversely, suppose that is compact. Then, is bounded. Let , we obtain
This shows that Consider now a sequence in such that as . If such a sequence does not exist, then condition (41) obviously holds.
Moreover, let us introduce a sequence of test functions :
Differentiation gives
From (29) and Lemma 15, it follows that there exists a constant , such that
This shows that , and
Taking , we have . This implies that . If E is a compact subset of , for , we have that has a positive lower bound. Thus, we have on all compact subsets of . According to Lemma 12, we have that . Hence,
□
Corollary 2.
For , we are back to the case of the unit ball , and is compact if and only if and
when . Also, in this case, the result is analog to that obtained by Li and Stević in [11].
Author Contributions
Writing—original draft, J.W. and J.S. All authors have read and agreed to the published version of the manuscript.
Funding
This research was supported by The National Natural Science Foundation of China, Grant/Award Numbers: 11771184; Postgraduate Research & Practice Innovation Program of Jiangsu Province, Grant/Award Numbers: KYCX20 2210.
Data Availability Statement
Our arguments and results are all self innovative except for citations and we don’t have any experimental data.
Conflicts of Interest
The authors declare no conflict of interest.
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