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A note on rough singular integrals in Triebel-Lizorkin spaces and Besov spaces
Journal of Inequalities and Applications volume 2013, Article number: 492 (2013)
Abstract
This paper is concerned with the singular integral operators along polynomial curves. The boundedness for such operators on Triebel-Lizorkin spaces and Besov spaces is established, provided the kernels satisfy rather weak size conditions both on the unit sphere and in the radial direction. Moreover, the corresponding results for the singular integrals associated to the compound curves formed by polynomial with certain smooth functions are also given.
MSC:42B20, 42B25.
1 Introduction
Let , , be the n-dimensional Euclidean space and denote the unit sphere in equipped with the induced Lebesgue measure dσ. Let be a homogeneous function of degree zero and satisfy
For a suitable function h defined on and a polynomial with , where N is the degree of , we define the singular integral operators along polynomial curves in by
For , we denote by . Fefferman [1] first proved that is bounded on for provided that Ω satisfies a Lipschitz condition of positive order on and . Subsequently, Namazi [2] improved Fefferman’s result to the case . Later on, Duoandikoetxea and Francia [3] showed that is of type for provided that and , where , , denotes the set of all measurable functions h on satisfying the condition
It is easy to check that for . In 1997, Fan and Pan [4] extended the result of [3] to the singular integrals along polynomial mappings provided that and for with , where denotes the Hardy spaces on the unit sphere (see [5, 6]). In 2009, Fan and Sato [7] showed that is bounded on for some with , provided that for , and Ω satisfies the following size condition:
For the sake of simplicity, we denote
On the other hand, for , Fan et al. [8] showed that is bounded on for provided and , where
Moreover, see [9, 10] for the corresponding results of the singular integrals in the mixed homogeneity setting.
Remark 1.1 It should be pointed out that the functions class was originally introduced in Walsh’s paper [11] and developed by Grafakos and Stefanov [12] in the study of -boundedness of singular integrals with rough kernels. It follows from [12] that for , and for any , moreover,
We also remark that condition (1.3) was originally introduced by Fan and Sato in more general form in [7]. In addition, it follows from [[7], Lemma 1] that
In this paper, we consider the boundedness of on the Triebel-Lizorkin spaces and the Besov spaces, which contain many important function spaces, such as Lebesgue spaces, Hardy spaces, Sobolev spaces and Lipschitz spaces. Let us recall some notations. The homogeneous Triebel-Lizorkin spaces and homogeneous Besov spaces are defined, respectively, by
and
where , (), denotes the tempered distribution class on , for and satisfies the conditions: ; ; if . It is well known that
for any , see [13–15], etc. for more properties of and .
For , the operator is the classical Calderón-Zygmund singular integral operator denoted by T. In 2002, Chen et al. [16] proved that T is bounded on provided for some . Subsequently, Chen and Zhang [17] improved the result of [16] to the case for some . Furthermore, in 2008, Chen and Ding [18] showed that is bounded on for and if and . In 2010, Chen et al. [19] extended the result of [18] to the singular integrals along polynomial mappings provided that for with .
In light of aforementioned facts, a natural question is the following.
Question Is bounded on if and for some ?
In this paper, we will give an affirmative answer to this question. Our main results can be formulated as follows.
Theorem 1.1 Let be as in (1.2) and for some . Suppose that for some and satisfies (1.1). Then for and , there exists a constant such that
where is independent of the coefficients of .
Theorem 1.2 Let be as in (1.2) and for some . Suppose that for some and satisfies (1.1). Then for , and , there exists a constant such that
where is independent of the coefficients of .
By (1.5) and Theorems 1.1-1.2, we get the following results immediately.
Theorem 1.3 Let be as in (1.2) and for some . Suppose that for some and satisfies (1.1). Then for and , there exists a constant such that
where is independent of the coefficients of .
Theorem 1.4 Let be as in (1.2) and for some . Suppose that for some and satisfies (1.1). Then for , and , there exists a constant such that
where is independent of the coefficients of .
Remark 1.2 Obviously, by (1.5) and (1.8), our results can be regarded as the generalization of the results in [8] or [7], even in the special case or . Moreover, by (1.4)-(1.5), our results are also distinct from the ones in [18, 19].
Furthermore, by Theorems 1.1-1.4, and a switched method followed from [20], we can establish the following more general results.
Theorem 1.5 Let for some and for some with satisfying (1.1). Suppose that φ is a nonnegative (or nonpositive) and monotonic function on such that with , where C is a positive constant which depends only on φ. Then
-
(i)
for and , there exists a constant such that
where
-
(ii)
for , and , there exists a constant such that
The constant is independent of the coefficients of .
Theorem 1.6 Let φ, h and be as in Theorem 1.5. Suppose that for some with satisfying (1.1). Then
-
(i)
for and , there exists a constant such that
-
(ii)
for , and , there exists a constant such that
The constant is independent of the coefficients of .
Remark 1.3 Under the assumptions on φ in Theorem 1.5, the following facts are obvious (see [20]):
-
(i)
and if φ is nonnegative and increasing, or nonpositive and decreasing;
-
(ii)
and if φ is nonnegative and decreasing, or nonpositive and increasing.
Moreover, the inhomogeneous versions of Triebel-Lizorkin spaces and Besov spaces, which are denoted by and , respectively, are obtained by adding the term to the right-hand side of (1.6) or (1.7) with replaced by , where , , if . The following properties are well known (see [13, 14], for example):
Hence, by (1.8)-(1.10) and Theorems 1.5-1.6, we get the following conclusion immediately.
Corollary 1.7 Under the same conditions of Theorems 1.5 and 1.6 with , the operator is bounded on and , respectively.
The paper is organized as follows. After recalling and establishing some auxiliary lemmas in Section 2, we give the proofs of our main results in Section 3. It should be pointed out that the methods employed in this paper follow from a combination of ideas and arguments in [3, 19, 20].
Throughout the paper, we let denote the conjugate index of p, which satisfies . The letter C or c, sometimes with certain parameters, will stand for positive constants not necessarily the same one at each occurrence, but are independent of the essential variables.
2 Auxiliary lemmas
For given polynomial , we let for and for all . Without loss of generality, we may assume that for (or there exist some positive integers such that with for all ). Let and . For and , we define the measures by
It is clear that
We have the following estimates.
Lemma 2.1 Let for some and for some . For , and , there exists a constant such that
-
(i)
(2.2)
-
(ii)
(2.3)
where . The constant C is independent of the coefficients of .
Proof By the change of the variables, we have
On the other hand, it is easy to check that
Interpolating between (2.4) and (2.5) implies (2.2). Next, we prove (2.3). Let
By Van der Coupt lemma, there exists a constant , which is independent of the coefficients of and k such that
For , since is increasing in , we have
where . Let be as in Lemma 2.1, by the change of the variables and Hölder’s inequality, we have
where
Note that
Combining (2.6)-(2.7) with the fact that , we get (2.3). This proves Lemma 2.1. □
Lemma 2.2 [[19], Theorem 1.4]
Let and with being real-valued polynomials on . For , the operator given by
satisfies the following inequality
where is independent of the coefficients of for all .
Lemma 2.3 [[21], Proposition 2.3]
Let and , be two nonsingular linear transformations. Let be a lacunary sequence of positive numbers satisfying . Let and . Define the transformations J and by
and
Here, we use to denote the Dirac delta function on , denote the inverse transform of J and denote the transpose of G. We have the following inequalities:
for arbitrary functions and ;
for arbitrary functions and .
Lemma 2.4 For any and arbitrary functions , there exists a constant , which is independent of the coefficients of such that
for .
Proof Since when , we may assume that . By duality, it suffices to prove (2.10) for . Given functions with . It follows from the similar argument as in getting (7.7) in [4] that
where
By Hölder’s inequality, we have
By Lemma 2.2 and Minkowski’s inequality, we have for ,
Thus, by (2.11)-(2.12), we get
where we take and . This completes the proof of Lemma 2.4. □
Lemma 2.5 [[20], Lemma 2.1]
Let Γ, φ be as in Theorem 1.5. Suppose that for some , then we have .
Lemma 2.6 Let be given as in Theorem 1.5. Then
-
(i)
if φ is nonnegative and increasing, ;
-
(ii)
if φ is nonnegative and decreasing, ;
-
(iii)
if φ is nonpositive and decreasing, ;
-
(iv)
if φ is nonpositive and increasing, ,
where .
Proof We can get easily this lemma by Remark 1.3 and the similar arguments as in getting [[20], Lemma 2.3]. The details are omitted. □
3 Proofs of main results
For a function such that for and for . Let , and define the measures by
for and , where we use convention . It is easy to check that
In addition, by Lemma 2.1, we can obtain the following estimates (see also in [[4], (7.39)])
where .
Now, we are in a position to prove our main results.
Proof of Theorem 1.1 It follows from (2.1) and (3.2) that
By (3.5), to prove Theorem 1.1, it suffices to prove that for any ,
for and , where is independent of the coefficients of for .
For , we choose a Schwartz function such that
where . Define the operator by
Let . It is clear that and
Observe that we can write
Invoking the Littlewood-Paley theory and Plancherel’s theorem, we get
where
This together with (3.3)-(3.4) yields
where
and . In other words (by (1.8)),
Next, we will show that
for , , and . To prove (3.9), it suffices to prove that
for and , where C is independent of the coefficients of . In fact, (3.10) implies (3.9), that is,
which leads to (3.9). Now, we return to the proof of (3.10). Using Lemmas 2.3-2.4, the definition of and the similar argument in getting [[19], Proposition 2.3], one can check that
for . Using Lemma 2.3 again, for and arbitrary functions , we have
By duality and (3.11)-(3.12), we have
This proves (3.10). Interpolating between (3.8) and (3.9) (see [14, 22]), for and , we can obtain such that and
which together with (3.7) implies (3.6) and completes the proof of Theorem 1.1. □
Proof of Theorem 1.2 The proof of Theorem 1.2 is to copy the arguments in proving [[19], Theorem 1.2]. By Theorem 1.1 and (1.8), for , there exists a constant such that
Then for , and , we have
Theorem 1.2 is proved. □
Proofs of Theorems 1.5-1.6 Using Lemmas 2.5-2.6 and Theorems 1.1-1.2, we get Theorem 1.5. Theorem 1.6 follows from Theorem 1.5 and Remark 1.1. □
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Acknowledgements
The authors would like to thanks the referees for their careful reading and invaluable comments. This work was supported by the NNSF of China (11071200) and the NSF of Fujian Province of China (No. 2010J01013).
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Liu, F., Wu, H. & Zhang, D. A note on rough singular integrals in Triebel-Lizorkin spaces and Besov spaces. J Inequal Appl 2013, 492 (2013). https://doi.org/10.1186/1029-242X-2013-492
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DOI: https://doi.org/10.1186/1029-242X-2013-492