Submitted:
05 September 2023
Posted:
07 September 2023
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Abstract
In this paper, we establish certain Lp bounds for several classes of rough Marcinkiewicz integrals over surfaces of revolution on product spaces. By using these bounds and using an extrapolation argument, we obtain the Lp boundedness of these Marcinkiewicz integrals under very weak conditions on the kernel functions. Several previous results on Marcinkiewicz operators are essentially extended or improved. Our results represent natural extensions and improvements of several known results on Marcinkiewicz integrals over symmetric spaces.
Keywords:
rough integrals
; surfaces of revolution
; product domains
; Marcinkiewicz integrals
; extrapolation
1. Introduction
Throughout this article, we assume that ( or n) and is the Euclidean space of dimension . Also, we assume that is the unit sphere in equipped with the normalized Lebesgue surface measure .
For , we let
where h is a measurable function defined on and is a measurable function defined on , integrable over and satisfies the following:
For a suitable mapping , the parametric Marcinkiewicz integral operator along the surface of revolution is defined, initially for , by
where
We remark that the Marcinkiewicz operator is a natural generalization of the Marcinkiewicz operator along surface of revolution in the one parameter setting which is given by
The study of the boundedeness of the operator under various conditions on and has attracted the attention of many authors. For a sample of known results relevant to our study, the readers are referred to consult [1,2,3,4,5].
Our main focus in this paper is the operator . When and , we denote the operator by . In addition, when , then reduces to the classical Marcinkiewicz integral on product domains, which is denoted by . The investigation of the boundedness of the operator initiated in [6] in which the author proved the boundedness of under the condition . Subsequently, the boundedness of has attracted the attention of many authors. For instance, in [7] the authors proved the () boundedness of if . In addition, they pointed out that by adapting a similar argument as that used in [8] to the product space setting, the assumption is optimal in the sense that if we replace it by any weaker condition with , then may lose the boundedness. On the other hand, under the assumption belongs to with , it was proved in [9] that is of type for all and that the condition is optimal in the sense that we cannot replace it by with so that is bounded on . Here is a special class of block spaces introduced in [10]. Later on, the authors of [11] employed Yano’s extrapolation technique found in [12] to establish the boundedness of for all provided that belongs to either or to and for some , where here (for ) denotes the collection of measurable functions h such that
For a sample of past studies as well as more information about the applications and development of the operator , we refer the readers to see [7,9,13,14,15,16,17,18] and the references therein.
By the work done in these cited papers, many mathematicians have been motivated to study Marcinkiewicz operator along surfaces of revolution on product spaces of the form
where
The boundedness of the operator under different conditions on the functions , , , and h was discussed by many authors (one can consult [15,19,20].
Very recently, in [21] the authors studied the boundedness of the singular integral operators along surfaces of revolution on product domains which is defined by
where is a suitable mapping. Under various conditions on , the authors proved the boundedness of if belongs to either or to .
In light of the results in [20] regarding the boundedness of Marcinkiewicz operator and of the results in [21] regarding the boundedness of singular integral , a question arises naturally is the following:
Question: Under the same conditions as those imposed on in [21], is the operator bounded whenever for some and lies in either the space or in the space with ?
In this article, we shall answer this question in affirmative. Indeed, we have the following:
Theorem 1.
Let such that for any fixed , we have , are in , increasing and convex functions with . Suppose that for some and for some . Then there is a constant such that
for all .
Theorem 2.
Let Ω and h be given as in Theorem 1. Suppose that with is a generalized polynomial on . Then there is a constant such that
for all .
Theorem 3.
Let Ω and h be given as in Theorem 1. Suppose that , where is in , increasing and convex function with and P is a generalized polynomials given by with . Then there is a constant such that
for all .
Theorem 4.
Let Ω and h be given as in Theorem 1. Suppose that , where () is either a generalized polynomial or is in , increasing and convex function with . Then there is a constant such that
for all .
By the conclusions from Theorems 1-4 along with the extrapolation argument found in [12,22], we obtain the following:
Theorem 5.
Let Ω satisfy the conditions -. Suppose that h and Φ and ψ are given as in either Theorem 1, Theorem 2, Theorem 3, or Theorem 4.
If for some , then the inequality
holds for all ;
If , then the inequality
holds for all .
(1) The conditions on in Theorem 5 are optimal. In fact, they are the weakest conditions in their particular classes, (see [7,9]).
(2) For the special cases and , the authors of [18] confirmed the ( boundedness of whenever for some . This result is extended in Theorem 5 in which .
(3) For the special case with , our results give the boundedness of for all which is the full range.
(4) For the special case , Theorem 5 gives that is bounded on for all , which is the result established in [11]. Hence, our results essentially improve the main results in [11].
(5) The surfaces of revolutions considered in our Theorems 1–5 cover several important natural classical surfaces. For instance, our theorems allow surfaces of the type with , with , is a polynomial, , where each is a convex increasing function with .
Henceforward, the constant C denotes a positive real constant which not necessary be the same at each occurrence but independent of all the essential variables.
2. Preliminary Lemmas
We devote this section to introducing some notations and establishing some auxiliary lemmas. For and a suitable mapping on , we define the family of measures and its concerning maximal operators and on by
and
where is defined in the same way as but with replacing by .
Lemma 1.
Let with and satisfy the conditions -. Suppose that . For , let
Then there are constants and δ with such that for , we have
where .
Proof.
By Schwartz inequality, we get that
where Let . Then by Van der Corput’s lemma, we get
which when combined with the trivial estimate , we deduce that
where . Hence, by Hölder’s inequality we obtain that
By choosing so that , we get that the last integral is finite. Thus,
Similarly we have
Also, by the conditions - and a simple change of variable we have
By combine the last estimate with the trivial estimate , we get
Similarly, we have
Therefore, by combining the estimates -, we get which ends the proof of this lemma. □
Lemma 2.
Suppose that with satisfies the conditions -, with , , and . Then there is a real number such that the estimates
hold for all , where δ is the same as in Lemma 1, and indicates to the total variation of .
Proof.
It is clear that the estimate is obtained by the definition of . Thanks to Hölder’s inequality, we have
For the case , we deduce that
However, for the case , by using Hölder’s inequality we get that
Therefore, for either case of we have
where . Hence, Lemma 1 leads to
As and , we get that
Consequently,
The proof is complete. □
The following lemmas play a key role in proving our main results.
Lemma 3.
Let with and for some . Assume that such that for any fixed , we have , are in , increasing and convex functions with . Then for with there exists such that
and
Proof.
Thanks to Hölder’s inequality, we get that
Hence, by Minkowski’s inequality for integrals and Lemma 2.4 in [21], we deduce
where
and
Similarly, by Lemmas 2.5-2.7 in [21], we get; respectively, the following results.
Lemma 4.
Let h and Ω be given as in Lemma 3. Assume that with is a generalized polynomial on . Then for with , there exists such that
and
Lemma 5.
Let h and Ω be given as in Lemma 3. Assume that , where is in , increasing and convex function with and P is a generalized polynomial given by with . Then for with there exists such that
and
Lemma 6.
Let h and Ω be given as in Lemma 3. Assume that , where () is either a generalized polynomial or is in , increasing and convex function with . Then for with there exists such that
and
Lemma 7.
Let , with , with , and Φ be given as in either Theorem 1, Theorem 2, Theorem 3, or Theorem 4. Then, for arbitrary set of functions defined on , a constant exists such that the inequality
holds for all .
Proof.
We will follow a similar argument as in [16]. We point out here that we shall prove this lemma only whenever is given as in Theorem 1 since the proofs for the other cases follow the the same method except that we invoke Lemmas 4-6 instead of invoking Lemma 3. Also, we shall prove this lemma only for the case since for all . In this case, we have which gives that . We need to consider two cases.
Case 1. . By duality there exists a non-negative function such that and
By Schwartz’s inequality we have
Hence, we have
where . Notice that, since , then . Thus, by Lemma 3 and Hölder’s inequality,
Case 2.. By duality there esits a collection of functions defined on such that
and
where
3. Proof of main theorems
Assume that for some , for some and . It is clear that Minkowski’s inequality leads to
For , choose a set of smooth partition of unity defined on , and adapted to the interval with the following properties:
where is independent of the lacunary sequence .
Define the multiplier operators on by . Hence, for any , we have , which gives by Minkowski’s inequality that
where
Therefore, to prove Theorem 1, it suffices to prove that for any p satisfying , there exists such that
Let us first estimate the -norm for By Plancherel’s Theorem, Fubini’s Theorem, Lemma 2, we deduce
where and .
Next, we estimate the -norm of as follows: By employing a similar argument as that used in [23] along with the Littlewood-Paley theory and Lemma 7, we get
Finally, by interpolating between and , we obtain , which in turn finishes the proof of Theorem 1.
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