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R E S E A R C H

Open Access

Weighted boundedness for Toeplitz type

operators related to strongly singular integral

operators

Dazhao Chen

*

*Correspondence:

chendazhao27@sina.com Department of Science and Information Science, Shaoyang University, Shaoyang, Hunan 422000, P.R. China

Abstract

In this paper, we show the sharp maximal function estimates for the Toeplitz type operators related to the strongly singular integral operators. As an application, we obtain the boundedness of the operators on weighted Lebesgue and Triebel-Lizorkin spaces.

MSC: 42B20; 42B25

Keywords: Toeplitz operator; strongly singular integral operator; sharp maximal function; Triebel-Lizorkin space; weighted Lipschitz function

1 Introduction and Preliminaries

As a development of singular integral operators [, ], their commutators have been well studied. In [–], the authors prove that the commutators generated by the singular in-tegral operators andBMOfunctions are bounded onLp(Rn) for  <p<. Chanillo []

proves a similar result when singular integral operators are replaced by the fractional in-tegral operators. In [–], the boundedness for the commutators generated by the singu-lar integral operators and Lipschitz functions on Triebel-Lizorkin andLp(Rn) ( <p<)

spaces are obtained. In [, ], the boundedness for the commutators generated by the singular integral operators and the weighted BMO and Lipschitz functions on Lp(Rn)

( <p<∞) spaces are obtained. In [, ], some Toeplitz type operators related to the sin-gular integral operators and strongly sinsin-gular integral operators are introduced, and the boundedness for the operators generated byBMOand Lipschitz functions is obtained. In this paper, we will study the Toeplitz type operators related to the strongly singular integral operator and the weighted Lipschitz functions.

First, let us introduce some notation. Throughout this paper, Qwill denote a cube of

Rnwith sides parallel to the axes. For any locally integrable functionf, the sharp maximal

function off is defined by

M#(f)(x) =sup Qx

|Q|

Q

f(y) –fQdy,

where we writefQ=|Q|–

Qf(x)dx. It is well known that [, ]

M#(f)(x)≈sup

Qx

inf

cC

|Q|

Q

f(y) –cdy.

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Let

M(f)(x) =sup

Qx

|Q|

Q

f(y)dy.

Forη> , setMη(f)(x) =M(|f|η)/η(x). For  <η<  and ≤r<∞, set

,r(f)(x) =sup Qx

|Q|–/n

Q

f(y)rdy

/r

.

TheApweight is defined by []

Ap=

wLlocRn :sup

Q

|Q|

Q w(x)dx

|Q|

Q

w(x)–/(p–)dx

p–

<∞

,

 <p<∞,

and

A=

wLplocRn :M(w)(x)≤Cw(x), a.e..

TheA(p,q) weight is defined by [], for  <p,q<∞,

A(p,q) =

w>  :sup

Q

|Q|

Q

w(x)qdx

/q

|Q|

Q

w(x)–p/(p–)dx

(p–)/p

<∞

.

Given a non-negative weight functionw, for ≤p<∞, the weighted Lebesgue space

Lp(w) is the space of functionsf such that

fLp(w)=

Rn

f(x)pw(x)dx

/p

<∞.

Forβ> ,p>  and the non-negative weight functionw, letF˙,∞(w) be the weighted

homogeneous Triebel-Lizorkin space [].

For  <β<  and the non-negative weight functionw, the weighted Lipschitz space

Lipβ(w) is the space of functionsbsuch that

bLipβ(w)=sup Q

w(Q)+β/n

Q

b(y) –bQdy<∞.

Remark () Forb∈Lipβ(w),wAandxQ, it is well known that

bQbkQCkbLip

β(w)w(x)w

kQ β/n.

() Letb∈Lipβ(w) andwA. By [], we know that the spacesLipβ(w) coincide and the normsbLipβ(w)are equivalent with respect to different values of ≤p≤ ∞.

Definition LetT :SS be a bounded linear operator.T is called a strongly singular integral operator if it satisfies the following conditions:

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(ii) there exists a functionK(x,y)continuous away from the diagonal onRn×Rnsuch

that

K(x,y) –K(x,z)+K(y,x) –K(z,x)≤C|yz|δ|xz|n+δ/ε

if|yz|ε≤ |xz|for some <δ, <ε< , and (Tf,g) =Rn

RnK(x,y)f(y)g(x)dy dxforf,gSwith disjoint support;

(iii) for some( –ε)n/≤β<n/,TandT∗extend to a bounded operator fromLq(Rn)

intoL(Rn), where/q= / +β/n.

Letbbe a locally integrable function onRn. The Toeplitz type operator related toT is

defined by

Tb=

m

k=

Tk,MbTk,,

whereTk,are strongly singular integral operators or±I(the identity operator),Tk,are

bounded linear operators onLp(Rn) for  <p<,k= , . . . ,m,M

b(f) =bf.

Note that the commutator [b,T](f) =bT(f) –T(bf) is a particular case of the Toeplitz type operatorsTb. The Toeplitz type operatorsTbare non-trivial generalizations of the

commutator. It is well known that commutators are of great interest in harmonic analy-sis and have been widely studied by many authors [, ]. In [–], the boundedness of the strongly singular integral operator is obtained. In [], a sharp function estimate of the strongly singular integral operator is obtained. In [], the boundedness of the strongly sin-gular integral operators and their commutators is obtained. In [], the Toeplitz type oper-ators related to the strongly singular integral operoper-ators are introduced, and the bounded-ness for the operators generated byBMOand Lipschitz functions is obtained. Our works are motivated by these papers. The main purpose of this paper is to prove sharp maximal inequalities for the Toeplitz type operatorsTb. As applications, we obtain the weighted

Lp-norm inequality and the Triebel-Lizorkin space boundedness for the Toeplitz type

op-eratorsTb.

We need the following preliminary lemmas.

Lemma ([]) Let T be a strongly singular integral operator.Then T is bounded on Lp(w)

for wApwith <p<∞,and when(( –ε)n+ β)/β<u≤,  <u/vδ,T is bounded from Lu(Rn)into Lv(Rn).

Lemma ([]) For any cube Q,b∈Lipβ(w),  <β< ,and wA,we have

sup

xQ

b(x) –bQCbLipβ(w)w(Q)+β/n|Q|–.

Lemma ([]) For <β< ,  <p<∞,and wA∞,we have

fF˙β,∞ p (w)≈

sup

Q· 

|Q|+β/n

Q

f(x) –fQdx Lp(w)

≈sup

Q·infc

|Q|+β/n

Q

f(x) –cdx Lp(w)

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Lemma ([]) Let <p<∞and wr<Ar. Then,for any smooth function f for which the left-hand side is finite,

RnM(f)(x)

pw(x)dxC

RnM #

(f)(x)pw(x)dx.

Lemma ([]) Suppose that <η<n,  <s<p<n/η, /q= /pη/n,and wA(p,q).

Then

Mη,s(f)Lq(wq)CfLp(wp).

2 Theorems and proofs

We shall prove the following theorems.

Theorem  Let wA,  <β< ,b∈Lipβ(w),and((–ε)n+β)/β<s<n/β.If gLp(Rn) ( <p<∞)and T(g) = ,then there exists a constant C> such that,for any fC∞(Rn) andx˜∈Rn,

M#Tb(f)(x˜)≤CbLipβ(w)w(x˜)+β/n m

k= ,s

Tk,(f) (x˜).

Theorem  Let wA,  <β<min(,δ/ε), (( –ε)n+ β)/β<s<n/β,and b∈Lipβ(w).

If gLp(Rn) ( <p<∞)and T(g) = ,then there exists a constant C> such that,for any fC∞(Rn)andx˜Rn,

sup

Q˜x

inf

cRn

|Q|+β/n

Q

Tb(f)(x) –cdxCbLipβ(w)w(x˜)+β/n m

k=

MsTk,(f) (x˜).

Theorem  Let wA,  <β< , /q= /pβ/n,and b∈Lipβ(w).If gLp(Rn) ( <p<∞)

and T(g) = ,then Tbis bounded from Lp(w)to Lq(wq/pq(+β/n)).

Theorem  Let wA,  <β<min(,δ/ε),  <p<n/, /q= /pβ/n,and b∈Lipβ(w).

If gLp(Rn) ( <p<)and T

(g) = ,then Tbis bounded from Lp(w)toF˙,∞(wq/pq(+β/n)).

Proof of Theorem  It suffices to prove forfC∞(Rn) and some constantC that the

following inequality holds:

|Q|

Q

Tb(f)(x) –CdxCbLipβ(w)w(x˜) +β/n

m

k= ,s

Tk,(f) (x˜).

Without loss of generality, we may assumeTk,areT(k= , . . . ,m). Fix a cubeQ=Q(x ,d)

andx˜∈Q. We have the following two cases. Case .d> . Write

Tb(f)(x) =TbbQ(f)(x) =T(bbQ)χQ(f)(x) +T(bbQ)χ(Q)c(f)(x) =f(x) +f(x).

Then

|Q|

Q

Tb(f)(x) –f(x)dx

|Q|

Q

f(x)dx+

|Q|

Q

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ForI, by Hölder’s inequality, boundedness ofT, and Lemma , we obtain

|Q|

Q

Tk,M(bbQ)χQT

k,(f)(x)dx

|Q|

Rn

Tk,M(bbQ)χQT

k,(f)(x)s dx

/s

C|Q|–/s

Q

M(bbQ)χQT

k,(f)(x)s dx

/s

C|Q|–/s

Q

b(x) –bQTk,(f)(x) sdx

/s

C|Q|–/ssup

x∈Q

b(x) –bQ

Q

Tk,(f)(x)sdx

/s

C|Q|–/sbLipβ(w)

w(Q)+β/n |Q| |Q|

/sβ/n

|Q|–/n

Q

Tk,(f)(x)sdx

/s

CbLipβ(w)

w(Q)

|Q|

+β/n ,s

Tk,(f) (x˜)

CbLipβ(w)w(x˜)+β/nMβ,s

Tk,(f) (x˜),

thus

I≤ m

k=

|Q|

Q

Tk,M(bbQ)χQT

k,(f)(x)dx

CbLipβw(x˜)+β/n m

k= ,s

Tk,(f) (x˜).

ForI, byd>  and |xx|ε≤ |yx|forxQandy∈(Q)c, we obtain, forxQ,

Tk,M(bbQ)χ(Q)cTk,(f)(x) –Tk,M(bbQ)χ(Q)cTk,(f)(x)

(Q)c

b(y) –bQK(x,y) –K(x,y)Tk,(f)(y)dy

C

(Q)c

b(y) –bQ | x–x|δ |x–y|n+δ/ε

Tk,(f)(y)dy

Cdδ

j=

jd≤|yx|<j+d

jdnδ/εb(y) –bi+QTk,(f)(y)dy

+Cdδ

j=

jdnδ/ε|bj+QbQ|

jd≤|yx|<j+d

Tk,(f)(y)dy

CbLipβ(w)δ/ε

×

j=

–/ε

w(j+Q)

|j+Q|

+β/n

|j+Q|–/n

j+Q

Tk,(f)(y)sdy

/s

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×

j=

j–/εw(x˜)

w(j+Q)

|j+Q|

β/n

|j+Q|–/n

j+Q

Tk,(f)(y)sdy

/s

CbLipβ(w)w(x˜)+β/nMβ,s

Tk,(f) (x˜),

thus

I≤

|Q|

Q m

k=

Tk,M(bbQ)χ(Q)cTk,(f)(x) –Tk,M(bbQ)χ(Q)cT

k,(f)(x )dx

CbLipβ(w)w(x˜)+β/n m

k= ,s

Tk,(f)(x˜).

Case .d≤. SetQ˜ =Q(x,) and write

Tb(f)(x) =TbbQ(f)(x) =T(bbQ)χQ˜(f)(x) +T(bbQ)χ(Q˜)c(f)(x) =f(x) +f(x).

Then

|Q|

Q

Tb(f)(x) –f(x)dx

|Q|

Q

f(x)dx+

|Q|

Q

f(x) –f(x)dx=I+I.

ForI, since (( –ε)n+ β)/βs<∞, there existsqsuch thatr<s,  <r/qε, andTis

bounded fromLr(Rn) intoLq(Rn). By using the same argument as in the proof ofI , we get

|Q|

Q

Tk,M(bbQ)χQ˜Tk,(f)(x)dx

|Q|

Rn

Tk,M(bbQ)χQ˜Tk,(f)(x)

q dx

/q

C|Q|–/q

Rn

b(x) –bQ f(x) r

dx

/r

C|Q|–/q

Q˜

b(x) –bQ˜

r

+|bQ˜ –bQ|r Tk,(f)(x)rdx

/r

CbLipβ(w)|Q|–/q

w(Q˜)+β/n| ˜Q|–+w(x˜)w(Q˜)β/n

Q˜

Tk,(f)(x)rdx

/r

CbLipβ(w)dn(ε/r–/q)w(x˜)

w(Q˜)

| ˜Q|

β/n

| ˜Q|–/n

˜

Q

Tk,(f)(x)sdx

/s

CbLipβ(w)w(x˜)+β/nMβ,s

Tk,(f) (x˜),

thus

I≤ m

k=

|Q|

Q

Tk,M(bbQ)χQ˜Tk,(f)(x)dx

CbLipβw(x˜)+β/n

m

k= ,s

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ForI, by using the same argument as in the proof ofI, we get, forxQ,

Tk,M(bbQ)χ(Q˜)cT

k,(f)(x) –Tk,M

(bbQ)χ(Q˜)cT k,(f)(x

)

(Q˜)c

b(y) –bQK(x,y) –K(x,y)Tk,(f)(y)dy

C

(Q˜)c

b(y) –bQf(y) | x–x|δ |x–y|n+δ/ε

dy

Cdδ

j=

jdεnδ/ε

j+Q˜

b(y) –bj+Q˜Tk,(f)(y)dy

+Cdδ

j=

jdεnδ/ε|bj+Q˜ –bQ˜|

j+Q˜

Tk,(f)(y)dy

+Cdδ

j=

jdεnδ/ε|bQ˜ –bQ|

j+Q˜

Tk,(f)(y)dy

CbLipβ(w)

j=

–/ε

w(j+Q˜) |j+Q˜|

+β/n

|j+Q˜|–/n

j+Q

Tk,(f)(y)sdy

/s

+CbLipβ(w)

×

j=

j–/εw(x˜)

w(j+Q˜) |j+Q˜|

β/n

|j+Q˜|–/n

j+Q˜

Tk,(f)(y)s dy

/s

+CbLipβ(w)

j=

–/εw(x˜)

w(Q˜)

| ˜Q|

β/n

|j+Q˜|–/n

j+Q˜

Tk,(f)(y)sdy

/s

CbLipβ(w)w(x˜)+β/nMβ,s

Tk,(f) (x˜),

thus

I≤

|Q|

Q m

k=

Tk,M(bbQ)χ(Q)cTk,(f)(x) –Tk,M(bbQ)χ(Q)cTk,(f)(x)dx

CbLipβ(w)w(x˜)+β/n m

k= ,s

Tk,(f) (x˜).

These complete the proof of Theorem .

Proof of Theorem  It suffices to prove forfC∞(Rn) and some constantC

that the

following inequality holds:

|Q|+β/n

Q

Tb(f)(x) –CdxCbLipβ(w)w(x˜) +β/n

m

k=

MsTk,(f)(x˜).

Without loss of generality, we may assumeTk,areT(k= , . . . ,m). Fix a cubeQ=Q(x ,d)

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Case .d> . Similar to the proof of Theorem , we have

Tb(f)(x) =TbbQ(f)(x) =T(bbQ)χQ(f)(x) +T(bbQ)χ(Q)c(f)(x) =f(x) +f(x)

and

|Q|+β/n

Q

Tb(f)(x) –f(x)dx

|

Q|+β/n

Q

f(x)dx+

|Q|+β/n

Q

f(x) –f(x)dx=II+II.

By using the same argument as in the proof of Theorem , we get

II≤ m

k= C |Q|β/n sup

x∈Q

b(x) –bQ|Q|–/s

Q

Tk,(f)(x)sdx

/s

m

k=

bLipβ(w)

w(Q)

|Q|

+β/n

|Q|

Q

Tk,(f)(x)sdx

/s

CbLipβ(w)w(x˜)+β/n m

k=

MsTk,(f)(x˜),

II≤

|Q|+β/n

Q

(Q)c

b(y) –bQK(x,y) –K(x,y)Tk,(f)(y)dy dx

C

|Q|+β/n

Q

(Q)c

b(y) –bQ | x–x|δ |x–y|n+δ/ε

Tk,(f)(y)dy dx

Cdδ

j=

jdnδ/ε

j+Q

b(y) –bj+QTk,(f)(y)dy

+Cdδ

j=

jdnδ/ε|bj+QbQ|

j+Q

Tk,(f)(y)dy

CbLipβ(w)δ/ε

×

j=

j(βδ/ε)

w(j+Q)

|j+Q|

+β/n

|j+Q|

j+Q

Tk,(f)(y)sdy

/s

+CbLipβ(w)δ/ε

×

j=

jj(βδ/ε)w(x˜)

w(j+Q) |j+Q|

β/n

|j+Q|

j+Q

Tk,(f)(y)sdy

/s

CbLipβ(w)w(x˜)+β/n m

k= Ms

Tk,(f) (x˜).

Case .d≤. SetQ˜ =Q(x,), whereρ= (δβ)/(δ/εβ) <ε, and write

(9)

and

|Q|+β/n

Q

Tb(f)(x) –f(x)dx

≤ 

|Q|+β/n

Q

f(x)dx+

|Q|+β/n

Q

f(x) –f(x)dx=II+II.

By using the same argument as in the proof of Theorem , for (( –ε)n+ β)/βs<∞, there existsqsuch thatr<s,  <r/qε, andT is bounded fromLr(Rn) intoLq(Rn), and

we get

II≤ m

k=

|Q|

Q

Tk,M(bbQ)χQ˜T

k,(f)(x)dx

m

k=

|Q|β/n

|Q|

Rn

Tk,M(bbQ)χQ˜Tk,(f)(x)

q dx /qC m k= dβn/q

Rn

b(x) –bQ f(x)r dx /rC m k= dβn/q

Q˜

b(x) –bQ˜

r

+|bQ˜ –bQ|r Tk,(f)(x) r dx /rC m k=

bLipβ(w)dβn/q

w(Q˜)+β/n| ˜Q|–+w(x˜)w(Q˜)β/nQ˜

Tk,(f)(x)r dx /rC m k=

bLipβ(w)(n/s+β)–βn/qw(x˜)

w(Q˜)

| ˜Q|

β/n

| ˜Q|

˜

Q

Tk,(f)(x)sdx

/s

CbLipβ(w)w(x˜)+β/n m

k= Ms

Tk,(f) (x˜),

II≤ m

k=

|Q|+β/n

Q

(Q˜)c

b(y) –bQK(x,y) –K(x,y)Tk,(f)(y)dy dx

m

k= C |Q|+β/n

Q

(Q˜)c

b(y) –bQ | x–x|δ |x–y|n+δ/ε

Tk,(f)(y)dy dx

C

m

k= β

j=

jdρnδ/ε

j+Q˜

b(y) –bj+Q˜Tk,(f)(y)dy

+C m

k= β

j=

jdρnδ/ε|bj+Q˜bQ˜|

j+Q˜

Tk,(f)(y)dy

+C m

k= δ

j=

jdρnδ/ε|bQ˜ –bQ|

j+Q˜

Tk,(f)(y)dy

C

m

k=

bLipβ(w)

j=

j(βδ/ε)

w(j+Q˜) |j+Q˜|

+β/n

|j+Q˜|

s+Q

Tk,(f)(y)sdy

/s

+C m

k=

(10)

×

j=

jj(βδ/ε)w(x˜)

w(j+Q˜)

|j+Q˜|

β/n

|j+Q˜|

j+Q˜

Tk,(f)(y)sdy

/s

+C m

k=

bLipβ(w)

j=

jj(βδ/ε)w(x˜)

w(Q˜)

| ˜Q|

β/n

|j+Q˜|

j+Q˜

Tk,(f)(y)sdy

/s

CbLipβ(w)w(x˜)+β/n m

k=

MsTk,(f) (x˜).

This completes the proof of Theorem .

Proof of Theorem Choose  <s<pin Theorem , notice thatwq/pq(+β/n)A

∞ and

w/pA(p,q), and we have, by Lemmas , , and ,

Tb(f)Lq(wq/pq(+β/n))M

Tb(f) Lq(wq/pq(+β/n))

CM#Tb(f) Lq(wq/pq(+β/n))

CbLipβ(w) m

k=

,s

Tk,(f) w+β/nLq(wq/pq(+β/n))

=CbLipβ(w) m

k=

,s

Tk,(f) Lq(wq/p)

CbLipβ(w) m

k=

Tk,(f) Lp(w)

CbLipβ(w)fLp(w).

This completes the proof of Theorem .

Proof of Theorem Choose  <s<pin Theorem . By using Lemma , we obtain

Tb(f)F˙β,∞

q (wq/pq(+β/n))

CbLipβ(w) m

k=

MsTk,(f)w+β/nLq(wq/pq(+β/n))

=CbLipβ(w) m

k=

MsTk,(f) Lq(wq/p)

CbLipβ(w) m

k=

Tk,(f)Lp(w)

CbLipβ(w)fLp(w).

This completes the proof of the theorem.

(11)

Competing interests

The author declares that they have no competing interests.

Received: 1 August 2013 Accepted: 22 December 2013 Published:24 Jan 2014 References

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2. Stein, EM: Harmonic Analysis: Real Variable Methods, Orthogonality and Oscillatory Integrals. Princeton University Press, Princeton (1993)

3. Coifman, RR, Rochberg, R, Weiss, G: Factorization theorems for Hardy spaces in several variables. Ann. Math.103, 611-635 (1976)

4. Pérez, C: Endpoint estimate for commutators of singular integral operators. J. Funct. Anal.128, 163-185 (1995) 5. Pérez, C, Trujillo-Gonzalez, R: Sharp weighted estimates for multilinear commutators. J. Lond. Math. Soc.65, 672-692

(2002)

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13. Lin, Y, Lu, SZ: Toeplitz type operators associated to strongly singular integral operator. Sci. China Ser. A36, 615-630 (2006)

14. Muckenhoupt, B, Wheeden, RL: Weighted norm inequalities for fractional integral. Trans. Am. Math. Soc.192, 261-274 (1974)

15. Garcia-Cuerva, J: WeightedHpspaces. Diss. Math.162(1979)

16. Alvarez, J, Milman, M:Hpcontinuity properties of Calderón-Zygmund type operators. J. Math. Anal. Appl.118, 63-79

(1986)

17. Alvarez, J, Milman, M: Vector-valued inequalities for strongly singular Calderón-Zygmund operators. Rev. Mat. Iberoam.2, 405-426 (1986)

18. Fefferman, C: Inequalities for strongly singular convolution operators. Acta Math.124, 9-36 (1970) 19. Fefferman, C, Stein, EM:Hpspaces of several variables. Acta Math.129, 137-193 (1972)

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10.1186/1029-242X-2014-42

References

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