Abstract
In this paper, appropriate bounds for particular classes of parabolic Marcinkiewicz integrals along surfaces of revolution on product spaces are obtained. These bounds allow us to use Yano’s extrapolation argument to obtain the boundedness of the aforesaid integral operators under weak conditions on the kernels. These conditions on the kernels are the best possible among their respective classes. In this work, several previously known results on Marcinkiewicz integrals are fundamentally improved and extended.
MSC:
42B20; 42B25; 42B35
1. Introduction
In this article, we assume that and are the unit sphere in the d-dimensional Euclidean space equipped with the normalized Lebesgue surface measure .
Let be fixed numbers belong to the closed interval , and let be a mapping given by , where . For any fixed , one can easily check that is the decreasing function in . Accordingly, the equation has a unique solution represented by . Fabes and Riviére [1] proved that is metric in , and called the mixed homogeneity space related to .
For , let be referred to as the diagonal matrix
For the space , we consider the following transformation:
Therefore, , where is the Jacobian of the transforms,
In [1], the authors proved that is a function and that there exists a real constant satisfying .
Let ℧ be a measurable real valued function which is defined on and belongs to the space with the following properties:
In [2], Ding, Xue and Yabuta studied parabolic Marcinkiewicz integrals given by
where
In addition, they established the boundedness of for all whenever with . Thereafter, the boundedness of the operator under various assumptions on the kernels was investigated by many authors (see for instance [3,4,5,6]).
We indicate that the parabolic singular integral operator which is related to the integral operator is given by
The operator was studied by many researchers for a long time (we refer the readers to consult [1,7,8] among others).
The investigation of the Marcinkiewicz integral on product domains was considered by many authors (see for instance [9,10,11,12]).
For and , let and be fixed numbers; and for , let
where , , h is a measurable mapping on , and ℧ is a real-valued measurable mapping on , integrable over and satisfies the following:
For convenient functions , we consider the parabolic Marcinkiewicz operator
where
, , and .
When we consider the case and , we get that , , , , and . In this case, we denote by . Furthermore, when we take , , , and , then the operator reduces to the classical Marcinkiewicz integral on product spaces, which is denoted by . Many researchers were interested in studying the operator . For instance, Ding in [13] proved the boundedness of if . However, the authors of [14] showed that is bounded on for all under the same condition . Later, Choi in [15] improved the last results for the special case . Precisely, he confirmed the boundedness of provided that . In [16], the authors proved the ( ) boundedness of the operator if ℧ belongs to . Furthermore, they found that the condition is optimal in the sense that if we replace the space by the space with , then the operator will not be bounded on .
Al-Qassem in [17] established the boundedness of for all under the assumption ℧ belongs to the certain block space with . Moreover, he proved that the space is optimal in the sense that we cannot replace it by the space for any so that the operator is still bounded on . For more information about the development and applications of the operator , one can refer to [2,16,17,18], among other references.
The results in [16] were generalized by Al-Salman in [9] in which he proved the boundedness of for all under the conditions , , and . Very recently, this result was improved in [12], in which the authors satisfied the boundedness of for all , provided that , , for some , and for some , where (for ) refers to the class of all functions h that are defined on , are measurable and satisfy
The consideration of the mapping properties of rough integral operators related to surfaces has been given a great deal of attention by many mathematicians (see for example [19,20,21] and the references therein.)
In this article, we let denote the collection of all non-negative mappings that satisfy the following properties:
- (a)
- is strictly increasing and is monotone on ,
- (b)
- for a fixed constant and for a constant ,
- (c)
- on for a fixed constant .
Additionally, we let denote the collection of all non-negative mappings that satisfy the following properties:
- (a)
- is strictly decreasing and is monotone on ,
- (b)
- for a fixed constant and for a constant ,
- (c)
- on for a fixed constant .
We indicate here that the collections and were established and introduced in [18]. Some model examples for mappings belong to are with and , and functions belonging to are for and .
In view of the results in [9,12] on the boundedness of the operator along the curve and of the results on the boundedness of the rough operators along surfaces of revolution, we are prompted to ask the following natural question: is the rough parabolic operator along surfaces of revolutions bounded?
The main goal of this paper is to give an affirmative answer to the above question. In fact, we have the following:
Theorem 1.
Assume that h belongs to with and assume that ℧ belongs to the space with . Suppose that are in or . Then, there is a positive constant such that
for .
By the estimates in Theorem 1 and Yano’s extrapolation argument(see [7,22]), we establish the following result:
Theorem 2.
Assume that ℧ satisfies the conditions (1)–(2), and assume that h, ϕ and ψ are given as in Theorem 1.
If for some , then the inequality
holds for all ;
If , then the inequality
holds for all .
Noteworthy is the fact that, in Theorem 2, the boundedness of the operator is obtained for the full range of p, i.e., , whenever . However, when , we satisfy that is bounded only for . A natural question arising here is whether we obtain the boundedness of for whenever . We shall answer this question in the next theorem.
Theorem 3.
If for some , then is bounded on for all .
If for some , then is bounded on for all .
From Theorem 3, we see that the boundedness of is satisfied whenever the condition on ℧ is optimal only for . However, for the case , the boundedness of is obtained, but the condition on ℧ is not optimal.
Marcinkiewicz integrals operators are parts of the class of Littlewood-Paley g-functions. The theory of Marcinkiewicz integrals has a long history. This theory is of vast scope and utility due its role in dealing with many important problems arising in such parts of analysis as partial differential equations and several complex variables. Recent efforts in dealing with these operators have been mostly focused on finding the weakest possible kernel conditions under which boundedness holds.
Henceforward, the constant C signifies a positive real number that could be different at each occurrence but is independent of all essential variables.
2. Some Lemmas
This section is devoted to establishing some lemmas that will be needed to prove the main results of this paper. Let us first recall the following lemma from [7].
Lemma 1.
Suppose that ϕ belongs to or . For a suitable mapping g, we let the maximal function be defined on by
Then for there exists a positive constant such that
Lemma 2.
Assume that are in or . Define the maximal function on by
Then there is a constant such that the inequality
holds for all with .
Proof.
It is well known that , where = , and ∘ refers to the composition of the operators. Hence, by Lemma 1 we have
□
We shall need the following from [4]:
Lemma 3.
Let γ denote the distinct numbers of with , and let . Then for , there exists such that
Let . We define the family of measures and its related maximal operators and on by
and
where is defined similarly to with replacing by .
To prove Theorem 1, we need to establish the following lemmas.
Lemma 4.
Then, there exist positive constants C and δ with such that
where and denote the distinct numbers of , , respectively.
Proof.
We shall prove the lemma only for the case since for all . Thanks to the Schwartz inequality, we know that
where Let . Then using Lemma 3, we obtain
where . This in turn by Hölder’s inequality implies
Now, if we choose , we deduce that the last integral is finite, and hence
Similarly, we obtain
Now, to prove the other estimates in (4), we need to use conditions (1) and (2) and a simple change of variable to obtain
Thus, when the last estimate is combined with the estimate , we obtain that
Similarly, we know that
Lemma 5.
Assume that for some , for some , , and are given as in Theorem 1. Then for some positive constant C we have the following estimates
for all , where δ is the same as in Lemma 4, and is the total variation of .
Proof.
By the definition of , we immediately obtain (9). Furthermore, by Hölder’s inequality and a simple change in variables, we have
It is easy to see that if , we obtain
However, if , using Hölder’s inequality we obtain
Hence, in either case of , we have
where . Thus, by Lemma 4, we obtain
In addition, since and , we directly obtain that
and
Lemma 6.
Let , with and be given as in Theorem 1. Then, for every , there exists a positive constant such that for all ,
Proof.
By Hölder’s inequality, we obtain
Hence, using Minkowski’s inequality for integrals together along with Lemma 2, we obtain
□
Lemma 7.
We assume that with , with and belong to or . Then, for any functions on , a positive constant exists such that the inequality
holds for all .
Proof.
We will follow a similar argument employed in [23]. Since for all , it suffices to prove the lemma for the case . Thus, we have . Now, if , then by duality, there is a function which is non-negative and satisfies and
Thanks to Schwartz’s inequality, we deduce that
Thus, we obtain that
where . Since , we obtain , and since , we obtain, by Lemma 6 and Hölder’s inequality
On the other hand, if , then by the duality, there is a set of functions defined on with
such that
where
Again, since , then by the duality, a function exists that satisfies and
Therefore, by the last inequality, together with (13), the desired inequality holds for the case which in turn finishes the proof of this lemma. □
By adapting the same technique employed in proving Lemma 4 in [7] to the product space setting, it is easy to show the following result.
Lemma 8.
Assume that with , with and belong to or . Then for any functions on , there is a positive constant such that
and
Proof.
First, we consider the case . By following the same above arguments, we obtain, by the duality, there are functions defined on with
and satisfies
where
As , then again by the duality, there exists a function such that and
3. Proof of the Main Results
Proof of Theorem 1. The proof of this theorem mainly depends on the approaches used in [4,11,16,23], which have their roots in [24]. For an , let . Then, by Minkowski’s inequality, we obtain
Let . Then, we know that . In addition, for , let be a smooth partition of unity which is defined on , and adapted to the interval . Precisely, we have the following:
where does not depend on the lacunary sequence . We define the multiplier operators on by . Thus, for any , we obtain . This leads, by Minkowski’s inequality, to
where
Therefore, to prove Theorem 1, it is enough to show that
for any p satisfying and for some .
Let us first estimate the -norm for By using Plancherel’s Theorem, Fubini’s Theorem, Lemma 5, and similar procedures as those employed in [11], we obtain
where and .
On the other hand, the -norm for is estimated as follows: by invoking Lemma 7 together with the Littlewood–Paley theory and using in [11] we obtain
Now, we interpolate between (19) and (20), and immediately obtain (18). This finishes the proof of Theorem 1.
Finally, the proof of Theorem 3 can be obtained by following the above arguments, invoking Lemma 8 instead of Lemma 7 and then adapting Yano’s extrapolation method. Precisely, using Lemma 8, we get that
for all , and
for all . Consequently, when we interpolate (19) with (21) and (22), we obtain (18). The proof of Theorem 3 is complete.
4. Conclusions
In this work, we obtained suitable estimates for a certain class of parabolic Marcinkiewicz integral operators when with . Using these estimates together with Yano’s extrapolation argument, we proved the boundedness of the aforesaid operator under very weak assumptions on ℧. Actually, we proved our results when for some which are considered to be the best possible in their respective classes. Furthermore, we established the boundedness of our operator for the full range under stronger conditions on ℧. Our results improve as well as extend numerous known results in the Marcinkiewicz operators.
Author Contributions
Formal analysis and writing—original draft preparation: M.A. and H.A.-Q. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
No data were used to support this study.
Acknowledgments
The authors would like to express their gratitude to the referees for their valuable comments and suggestions in improving writing this paper. In addition, they are grateful to the editor for handling the full submission of the manuscript.
Conflicts of Interest
The authors declare that they have no conflict of interest.
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