Submitted:
20 April 2023
Posted:
21 April 2023
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Abstract
The main goal of this article is the characterization of Herz-type Besov-Morrey spaces K˙p,qαN˙μ,rs and Triebel-Lizorkin-Morrey spaces K˙p,qαE˙μ,rs via ball means of differences, atomic, molecular and wavelet decompositions. There are provided necessary facts for implying these results, which can help to explore such spaces on different domains in further researches. Proposed spaces allow to extend the class of studying functions, containing Leray projection, heat semi-group and other operators, which can be helpful in exploring weak, strong and mild solutions of nonlinear partial differential equations.
Keywords:
Herz-type Besov-Morrey spaces
; Herz-type Triebel-Lizorkin-Morrey spaces
; ball mean of differences
; atomic and molecular decomposition
; wavelet decomposition
1. Introduction
Attempts to define function spaces, using different approaches, takes its beginning since the appearance of Hardy, Besov and Triebel-Lizorkin spaces, which help to advance the studying nonlinear PDEs. On example, Besov spaces characterized via ball means of differences allowed to establish higher integrability results for the gradient of local weak solutions to the strongly degenerate or singular elliptic PDE in [1]. Another example is Triebel-Lizorkin spaces defined via Fourier transforms, which allowed to explore mild solutions of Navier-Stokes equation in [2].
There are 3 ways to define any function space [3]: Fourier-analytic, derivatives and differences and bounded mean oscillation. Specifying spaces in various ways allows to extend their properties, which can help in the study of PDE solutions, the behavior of pseudo-differential operators, Riemannian manifolds with the corresponding metric, Lie groups and fractals.
The study of quasi-norms, atomic, molecular and wavelet decompositions remains actual since the definition of local Hardy spaces in [4]. Such research was continued on Lorentz spaces for exploring weak and strong solutions of the nonlinear heat equation in [5]. The similar work was realized for Navier-Stokes equations and Keller-Segel system on Besov and Triebe-Lizorkin spaces in [6]. Afterwards, many researchers came up with the idea of combining function spaces into one function spaces, which can be global or hybrid, well described in [7] and [8], respectively.
Examples of hybrid spaces were demonstrated in [9], where the author researched the Caffarelli-Kohn-Nirenberg inequalities on Herz-type Besov spaces and Triebel-Lizorkin spaces and presented their quasi-norms, applying Fourier transforms and ball means of differences. Such spaces allowed to combine the properties of Besov, Triebel-Lizorkin and Herz spaces. Another example of hybrid spaces is Besov-weak-Herz spaces introduced in [10], where authors explored mild solutions of the incompressible Navier-Stokes equations. There were provided -method real interpolations, embeddings and heat semi-group operator inequalities for obtaining estimates of mild solutions on Besov-weak-Herz spaces . The combining of Besov and weak Herz spaces generalized and extended their properties, what allowed to receive valuable results in the studying the Navier-Stokes equations. The unique maximal strong solution and the local strong well-posedness of the Navier–Stokes equations with was constructed on Triebel-Lizorkin-Lorentz spaces in [11], which provided important inequalities containing the Laplace and the Stokes operators.
The main idea of this article arose from the researching quasi-norm characterizations via ball means of differences on Besov-Morrey spaces and Triebel-Lizorkin-Morrey spaces, which are investigated in [12] and [13], the exploring of the atomic decomposition of Herz-type Besov and Triebel-Lizorkin spaces, and the wavelet decomposition for the corresponding spaces in [14]. The definition of Herz-type Besov and Triebel-Lizorkin spaces via differences in [15] impacted to the topic of this research. In this article, we propose Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey spaces, denoted by and , respectively. We establish equivalence between the quasi-norms defined via ball of means differences and Fourier transforms, imply atomic, molecular and wavelet decomposition for corresponding spaces. Taking into account the quasi-norm of Herz spaces, we imply helpful inequalities on Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey spaces, containing Hardy-Littlewood and Peetre maximal operators. The proposed spaces were not present in other papers, then the necessary facts on , where , are not provided. Therefore, there are provided some inequalities, containing maximal functions, embeddings and isomorphisms in this article.
The remaining of the paper is organized as follows. Section 2 is devoted to definition of proposed spaces via Fourier-analytic approach. Section 3 contains necessary theorems, lemmas and propositions for further proofs. In section 4 we characterize Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey spaces, utilizing the ball means of differences. Section 5 and section 6 present atomic, molecular and wavelet decompositions, respectively.
2. Definition of Herz-Type Besov-Morrey and Triebel-Lizorkin-Morrey Spaces via Fourier-Analytic Approach
We should provide some helpful notations, which shorten the writing of formulas. Let be a sequence of functions, then we note
where and is the set of all non-negative integers. For definiteness we adopt the following definition as the Fourier transform and its inverse:
for every f in the space of tempered distributions .
Before giving the definition of the Herz spaces, let us introduce the following notations. Let . Then
For , we denote
Let us recall the definition of homogeneous Herz spaces [9].
Definition 1.
Let and . The homogeneous Herz spaces are defined as
where
with the usual modification when .
The spaces are quasi-Banach spaces, and if then are also Banach spaces. When and the space coincides with the Lebesgue space . In addition , where
Let be an open ball in centered at and radius . Next we define the Herz-type Morrey space.
Definition 2.
Let , and , then Herz-type Morrey spaces are defined as the sets of functions such that
Let and be Schwarz and the tempered distributions spaces, respectively. Suppose, that is a nonegative radial function such that
and
where . Using a partition of unity, we can define Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey spaces via Fourier-analytic approach.
Definition 3.
For , , and ,
(i) the inhomogeneous Herz-type Besov-Morrey space is the set of , where is the set of polynomials, such that and
with the usual modification when .
(ii) the inhomogeneous Herz-type Triebel-Lizorkin-Morrey space is the set of , where is the set of polynomials, such that and
with the usual modification when .
Let us introduce the Hardy-Littlewood maximal operator:
And we note , . Suppose that , , , and , then we introduce the Peetre maximal function defined as
These maximal operators are useful for characterization of Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey spaces via ball means differences.
In this section introduced spaces were defined via Fourier analytic approach. This approach was useful in [16], where estimates of mild solutions of the Navier-Stokes equation, containing semi-group heat operator on weak Herz-type Besov-Morrey spaces, were explored. The Fourier-analytic approach on Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey spaces facilitates the studying of mild solutions of nonlinear PDEs, where the heat semi-group operator and the Lerray projection are intensively engaged. For example, a mathematical model of waves on shallow water surfaces described by Korteweg-de Vries equation [17], Keller–Segel System [18] presents a cellular chemotaxis model, or Fokker-Planck equations [19] demonstrates models of anomalous diffusion processes. The developing of atomic, molecular and wavelet decompositions can advance the studying of and spaces on smooth and singular manifolds, especially observing them not only using the Fourier-analytic approach, but also using the difference approach.
3. Properties of Herz-Type Besov-Morrey and Triebel-Lizorkin-Morrey Spaces
In this section we provide useful inequalities and properties of spaces , where .
Lemma 1.
Let ; ; ; and , then we get the following inequality:
Proof. This inequality implied from Lemma 1 [20] and Minkowski inequality for infinite sums. In case, when
Analogical calculations we apply in case and receive the required inequality. □
According to Lemma 1, it is possible to obtain the general inequality for the arbitrary family of functions.
Corollary 1.
Let ; ; ; and is the family of functions in , then we get the following inequality:
We also verify the relation between f and in the next lemma.
Lemma 2.
Let , and .
(i) If , then .
(ii) If , then
holds for all .
Proof. (i) We use the Hölder inequality and represent , where is the Dirac -function, and there exists some l and t such that
(ii) Using direct manipulations we receive
□
Now it is necessary to provide helpful inequalities, containing Hardy-Littlewood and Peetre maximal functions.
Theorem 1.
Let , and , then
(i) For all we have
In addition, for a sequence of we have
(ii) For of we have
Proof. According to Lemma 5 from [21], we obtain (10)-(11). Therefore, from (i) we receive (ii). □
We should to collect some basic properties of Herz-type Besov- Morrey and Triebel-Lizorkin-Morrey spaces.
Theorem 2.
Let , , , , , and .
(i) If , then we have
(ii) If we assume , then we have
Proof. The estimates (i) and (ii) are the consequences of Theorems 5.4 and 5.5 from [22], is a constant function. □
Proposition 1.
Let ; ; ; , then
(i) If , then we have .
(ii) If , then we have .
(iii) for .
Let us imply the Hardy-type inequality, containing the norm of , which is a corollary of Lemma 3.9 from [23].
Lemma 3.
Let ; ; and . Let be a sequence of non-negative measurable functions on and
Then we have
and
From [23] we provide useful inequality.
Lemma 4.
Let , and . We define
for with supp, then we have
for all .
Remark, that is defined in section 4.
For atomic, molecular and wavelet decompositions we need to introduce the following facts. Let . Then for all there holds
Now, we consider the lifting properties. If , then operator is defined as
It is well-known that is an one to one mapping on and , respectively. Moreover, the equality is valid for all .
Theorem 3.
Let , , , , . Then . Moreover,
are equivalent quasi-norms on .
Proof. If , by the estimate , we have
where C does not depend on f. Therefore, is continuous.
If and
Hence, by (14) and (15), is an isomorphism.
Next, we prove that the quasi-norm, containing , is an equivalent quasi-norm on . For let , where . If , , then we get
where the last inequality is obtained by (15).
Finally, we assume that and for . We claim that there exist Fourier multipliers on , and positive constant C such that , for all . Then we have
However, . By Fourier multiplier properties of , we obtain
By (16) and (17), we prove that the quasi-norms, containing partial derivatives, are equivalent quasi-norms on . □
It is possible to provide the corollary of Theorem 3.
Corollary 2.
Let ; ; ; and . Then
(i) ,
(ii) ,
(iii)
(iv)
are isomorphic.
Let us provide three useful statements, which can help to prove atomic and molecular decompositions.
Lemma 5.
Let ; ; α, s ,r and . Any atom belongs to . Furthermore any compactly supported function a with . Then .
Proof. If is a function supported on the unit ball and , then , where c is a constant.
Let us decompose
where is a homogeneous polynomial of degree . We set . With this decomposition we obtain
From this expression we see that, for every , there exists a constant such that the estimate
holds for every and . From this estimate we can get
and
for .
What remains to be dealt with is the assertion that any atom centered at belongs to . This can be achieved by using the partition of unit and what we have proved for such that and , where means a cube. The strong decay condition gives us the desired convergence. □
Let us define and , where is a large integer depending on the parameters . Let for . Next theorem is a generalization of Theorem 4.1 from [14], where instead of Morrey spaces used Herz-type Morrey spaces.
Theorem 4.
Suppose that , , and . There exists a constant c such that
(i) ,
(ii) .
Lemma 6.
Suppose that ; , and . Let be an integer satisfying
For we are given an atom centered at .
Assume addition, that a doubly indexed sequence belongs to . Then the series
converges in .
Proof. The convergence in of the sum is proved in Lemma 4.5 in [14] for molecules and atoms. Let , then in the case of with we obtain
This gives us the convergence of in . □
Proposition 2
4. Difference and Local Means Approach
Let f be an arbitrary function on and . Then
where – binomial coefficients.
Under the ball means of differences, we mean the quantity
which is used to characterize via the ball means of differences.
Definition 4.
For , , and , the homogeneous Herz-type Besov-Morrey space is the set of , where is the set of polynomials, such that
Analogically, we define Herz-type Triebel-Lizorkin spaces using the ball means of differences.
Definition 5.
For , , and , the homogeneous Herz-type Triebel-Lizorkin-Morrey space is the set of , where is the set of polynomials, such that
Additionally, we provide discrete quasi-norms for , :
Afterwards, we establish the equivalence between quasi-norms , and for all .
Theorem 5.
Let , , , , and :
(i) If , then holds if and only if and . Furthermore, and are equivalent. The same statement holds for .
(ii) If , then holds if and only if and . Furthermore, and are equivalent. The same statement holds for .
Proof. 1) First we need to prove that quasi-norms and are equivalent. It is easy to see that
If , then and
According to (18) and the right-hand side of (19) we obtain
It shows that . The inequality is implied by (18) and the left hand side of (19). The same technique we use for .
2) (i) Before proving the inequality
it is necessary to show that . By and Proposition 1, we have
Let with for and supp(. For
We use the decomposition , where if . Hence, for one receives
For receiving the desired inequality (20) it suffices to prove , where .
If r > 1, by Minkovski inequality, we get
In this case it suffices to prove , where .
We estimate and , using Lemma 4 in the form
and
We use estimate with instead of h and obtain
In fact , ( and ).
If , by and , where , we see that
By the boundness of Peetre maximal function (Theorem 2), we get
If ,
Therefore, we have
We consider the and . Let when . Otherwise, there is a such that and . This implies that there exists a real number such that and .
By Lemma 4, we see that
where is maximal Hardy-Littlewood operator.
If , we denote
and
Let . By Hölder inequality, we obtain
The Hölder inequality [9] implies that
By (23), Lemma 1 and Theorem 1,
Next we estimate , when . By Hölder inequality we have
Using the similar arguments as in (24), we have
(ii) Now we prove . According to the definition of quasi-norm , we consider quasi-norm of
We split into two parts as below, applying , :
Firstly we prove . Let
Then by (21), it is easy to see that
Thanks to Lemma 3 and Theorem 2 with , we obtain
Finally, we shall prove .
Due to conditions , we can choose such a real number a. Let , by (22) we have
Let . By Lemma 1, (23) and Hölder inequality, we see that
Therefore, by Theorem 1, we obtain
3) We prove that for . Let with whem and when . We define
Note that with when and when . We define for . The family is a partition of unity, and that
Let and for . Take . By , holds for all . Then we can estimate
We put for . We see that
By virtue Lemma 3, we have
Finally .
Using (25) with and applying Lemma 3 we have
□
5. Atomic Decomposition
Let us introduce the following definition.
Definition 6.
1. Let and . Then we define
2. Let , and . Then we define the p-normalized indicator by
3. Let , , . Let double-indexed sequences then we denote and as Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey sequence spaces, which have corresponding quasi-norms:
Now we bring the definition of [K, L]-atoms.
Definition 7.
Let and , where and .
1. The function is called an [K, L]-atom centered at for , if and for all with .
2. The function is said to an [K, L]-atom centered at for and , if , for all with and
for with .
3. The function is called an [K, L]-atom centered at for , if
if .
4. The function is called an [K, L]-atom centered at for and , if
if and
for .
Here and below we always assume that . Let us define the following values:
where n is an dimension.
Additionally, we define the [K, L, M]-molecules.
Definition 8.
Let and , where and . The function is called a [K, L, M]-molecule concentrated in , and , if
for and
for .
Theorem 6.
Let be fixed. Suppose that the parameters and satisfy , , , , for -scale and , , , for -scale.
1)Assume that is a family of atoms and . Then for sum converges in and belongs to with the norm estimate
2) Conversely, any admits the following decomposition:
which converges in . We can average the family of atoms such that the family of coefficients fulfills the norm estimate
Proof. 1) By Lemma 6 we may assume that the coefficients are zero with finite exception. In this case we have that by Lemma 5. To measure this norm we use Theorem 4. Let with . Then
We take a homogeneous polynomial of degree with , which met in proof of Lemma 5. Then . As result we obtain
Using Peetre inequality and taking into account that , we obtain
As a consequence, we have
Then we get
Multiplying by to both sides and adding the above inequality over , we obtain
Note that a satisfying comparable to . Therefore,
where is sufficiently close to . Since M is assumed sufficiently large, we add
Let . Then if , we have
where and
If , then the mean value theorem gives us
Therefore, we obtain
If , then we use
By this estimate, we obtain
Combining (28) and (29), we obtain
We multiply to the above inequality and add it over .
Let be a constant smaller than . Then we obtain, by using ,
Taking into account (27), we are led to
where .
As before by the Hölder inequality we obtain
This inequality and the Fefferman-Stein vector-valued maximal inequality (10) yield (31). Thus, we have the desired result.
2) () Let be constant larger that and . Assume that a family for . . We also take such that supp. For set and we define uniquely so that . Then
Let us set and
Then . Lemma 4.11 yields .
() Let be constant larger that and can be decomposed as
Observe that by virtue of Theorem 3 provided M is large enough. Let - compactly supported function with . Suppose that supp.
We define coefficients and functions by
Next we note that
We decompose
and use (13) to obtain a pointwise estimate,
where lightly less than . Taking into account the triangle inequality
and with help of Theorem 3, we receive
As a result if M is large enough. Application of Theorem 3 and combination of (32) and (33) give us
Next we can see with , , we obtain . Here and b satisfy the following conditions:
1. .
2. supp(
3. for .
Thus, if we set and , we get . □
Corollary 3.
Under the same condition in Theorem 6 with
1) For the family of [K, L, M]-molecules and the sum converges in and belongs to with the norm estimate
2) Conversely any admits the decomposition , which converges in . We can average the family of [K, L, M]-molecules and that coefficients fulfill the norm estimate
6. Wavelet Decomposition
Let and let , are real-valued compactly supported functions with
The function is called scaling function (or father wavelet) and is called an associated function (mother wavelet).
Let where ∗ indicates that at least one of the components of G must be an M. Then we set
where . The family is called (Daubechies) wavelet system.
for .
Definition 9.
Let , , and .
(i) Then define
where
(ii) Let . Define
where
Theorem 7.
Suppose that the parameters , , and . Let N be a large integer depending on .
1. Suppose that we are given and in for each . Then
belongs to and satisfies
2. Conversely, any admits the following decomposition
and the coefficients satisfy
Proof. Fix . Choose so that
where and are even and real-valued. Let us define and by
for . Applying this, we receive
Observe that
By virtue of the fact that has vanishing moment of any order we see that there exist and such that
for all with . As a consequence, it follows that
Choose so that when and that when . Inversing this estimate and invoking Proposition 2, we obtain
for all . Then we have
If we combine the above inequalities, it follows that
Integrating this inequality, we obtain
for all .
Now using this pointwise estimate, we obtain
With this estimate and Theorem 1 (ii), we obtain (37). □
7. Conclusion
This article focused on characterization via ball means of differences, atomic, molecular and wavelet decompositions of Herz-type Besov-Morrey and Triebel-Lizorkin-Morrey spaces. There were introduced main definitions in preliminaries and necessary facts for proofs of Theorems 5, 6 and 7 in section 3. They can help to explore Fourier-multipliers, quarkonial decomposition, traces on Riemannian manifolds and fractals. Proposed spaces defined via ball means of differences find their application in the studying of solutions of partial differential equations such as Navier-Stokes, Klein-Gordon, Korteweg–de Vries and Burgers equations. Atomic, molecular and wavelet decompositions can imply useful properties in pseudo-differential operators theory, global and geometric analyses, which include Riemannian manifolds, Lie groups and fractals.
The provided characterizations and decompositions can be useful for determining the Fourier multipliers, as it was done in [24]. Also, they can help us to explore quarkonial decomposition, traces on Riemannian manifolds and fractals. Moreover, it is possible to extend researches on the set of analytic functions on CR-manifolds.
Author Contributions
Conceptualization, R.A.; Formal analysis, R.A.; Funding acquisition, P.L.,R.A.; Investigation, R.A.; Methodology, P.L.; Project administration, P.L.; Resources, R.A.; Supervision, P.L.; Writing—original draft, R.A.; Writing—review and editing, P.L. All authors have read and agreed to the published version of the manuscript.
Funding
The work is supported by North-Caucasus Center for Mathematical Research under agreement No 075-02-2023-938 with the Ministry of Science and Higher Education of the Russian Federation.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Acknowledgments
The authors would like to thank the North-Caucasus Federal University for supporting in the contest of projects competition of scientific groups and individual scientists of the North-Caucasus Federal University.
Conflicts of Interest
The authors declare no conflict of interest.
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