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Some sharp inequalities for multilinear integral operators
Journal of Inequalities and Applications volume 2013, Article number: 445 (2013)
Abstract
In this paper, some sharp inequalities for certain multilinear operators related to the Littlewood-Paley operator and the Marcinkiewicz operator are obtained. As an application, we obtain the -norm inequalities and Morrey spaces boundedness for the multilinear operators.
MSC:42B20, 42B25.
1 Introduction and results
In this paper, we study some multilinear operators related to some integral operators, whose definitions are as follows.
Fix . We denote and the characteristic function of by . Suppose that are the positive integers (), and are the functions on (). Let
Definition 1 Let and ψ be a fixed function which satisfies the following properties:
-
(1)
,
-
(2)
,
-
(3)
when .
The multilinear Littlewood-Paley operator is defined by
where
and for . Set . We also define that
which is the Littlewood-Paley operator (see [1]).
Let H be the Hilbert space . Then for each fixed , may be viewed as a mapping from to H, and it is clear that
Definition 2 Let and Ω be homogeneous of degree zero on with . Assume that , that is, there exists a constant such that for any , . The multilinear Marcinkiewicz operator is defined by
where
Set
We also define that
which is the Marcinkiewicz operator (see [2]).
Let H be the Hilbert space , then for each fixed , may be viewed as a mapping from to H, and it is clear that
Note that when , and are just the multilinear commutators (see [3, 4]). While when , and are non-trivial generalizations of the commutators. It is well known that multilinear operators are of great interest in harmonic analysis and have been widely studied by many authors (see [5–9]). In [10], Hu and Yang proved a variant sharp estimate for the multilinear singular integral operators. In [11–13], authors proved a sharp estimate for the multilinear commutator. The main purpose of this paper is to prove the sharp inequalities for the multilinear integral operators and when for all α with . As an application, we obtain the -norm inequalities and Morrey spaces boundedness for the multilinear operators.
First, let us introduce some notations. Throughout this paper, Q will denote a cube of with sides parallel to the axes. For any locally integrable function f, the sharp function of f is defined by
where, and in what follows, . It is well-known that (see [14, 15])
We say that f belongs to if belongs to and . For and , let
we write that , which is the fractional maximal operator.
Fixed . For , let
where . The Morrey spaces are defined by (see [16–20])
As the Morrey space may be considered as an extension of the Lebesgue space, it is natural and important to study the boundedness of the multilinear integral operator on the Morrey space.
We shall prove the following theorems.
Theorem 1 Let for all α with and .
-
(1)
Then there exists a constant such that for any , and ,
-
(2)
If and , then is bounded from to , that is,
-
(3)
If , , , then is bounded from to , that is,
Theorem 2 Let for all α with and .
-
(1)
Then there exists a constant such that for any , and ,
-
(2)
If and , then is bounded from to , that is,
-
(3)
If , , , then is bounded from to , that is,
Remark The conclusions of Theorems 1 and 2 are completely the same. Thus, they explain that the Littlewood-Paley and Marcinkiewicz operators have the many similar bondedness properties.
2 Proofs of theorems
To prove the theorems, we need the following lemmas.
Lemma 1 [7]
Let A be a function on and for all α with and some . Then
where is the cube centered at x and having side length .
Lemma 2 [21]
Suppose that and . Then
Let and . Then the following estimates hold:
-
(a)
;
-
(b)
for and .
Lemma 4 Let and . Then and are all bounded from to .
Proof For , by Minkowski inequality and the condition of ψ, we have
noting that when and
we obtain
For , note that , when , , we have
Thus, the lemma follows from [21]. □
Proof of Theorem 1 (1) It suffices to prove for and some constant , the following inequality holds:
Without loss of generality, we may assume . Fix a cube and . Let and , then and for . We write, for and ,
then
thus,
Now, let us estimate , , , and , respectively. First, for and , by Lemma 1, we get
Thus, by the -boundedness of , for and , we obtain
For , denoting for , , and , we have, by Hölder’s inequality,
For , similar to the proof of , we get
Similarly, for , denoting for , , and , we obtain
For , we write
By Lemma 1 and the following inequality (see [15])
we know that, for and ,
Note that for and , we obtain, similar to the proof of Lemma 4,
For and , by the formula (see [7])
and Lemma 1, we have
Thus, similar to the proof of Lemma 4,
Similarly, we get
For , taking such that , then
Thus
We choose in (1), then (2) follows from Lemma 2. For (3), taking in (1) and by Lemma 3, we obtain
This completes the proof of Theorem 1. □
Proof of Theorem 2 It is only to prove (1). Let Q, , , and be the same as the proof of Theorem 1. We write
then
Similar to the proof of Theorem 1, we get
For , we write
Then, similar to the proof of Lemma 4 and Theorem 1, we get
The same argument as the proof of Theorem 1 will give the proof of (2) and (3), we omit the details and finish the proof. □
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Lu, D. Some sharp inequalities for multilinear integral operators. J Inequal Appl 2013, 445 (2013). https://doi.org/10.1186/1029-242X-2013-445
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DOI: https://doi.org/10.1186/1029-242X-2013-445
Keywords
- multilinear operator
- Littlewood-Paley operator
- Marcinkiewicz operator
- Morrey space
- BMO