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We study the parabolic fractional maximal and integral operators MΩ,Pα and IΩ,Pα, 0<α<γ with rough kernels in the parabolic generalized Morrey space Mp,ϕ,P(Rn)

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Inequalities

Volume 9, Number 1 (2015), 257–276 doi:10.7153/jmi-09-23

PARABOLIC FRACTIONAL MAXIMAL AND INTEGRAL OPERATORS WITH ROUGH KERNELS IN PARABOLIC GENERALIZED MORREY SPACES

VAGIFS. GULIYEV ANDAYDINS. BALAKISHIYEV

(Communicated by S. Samko)

Abstract. LetPbe a realn×nmatrix, whose all the eigenvalues have positive real part,At=tP, t>0 , γ=trPis the homogeneous dimension on Rn andΩis anAt-homogeneous of degree zero function, integrable to a power s>1 on the unit sphere generated by the corresponding parabolic metric. We study the parabolic fractional maximal and integral operators MΩ,Pα and IΩ,Pα, 0<α<γ with rough kernels in the parabolic generalized Morrey space Mp,ϕ,P(Rn). Wefind conditions on the pair(ϕ1,ϕ2)for the boundedness of the operators MPΩ,α and IΩ,Pα from the spaceMp,ϕ1,P(Rn)to another oneMq,ϕ2,P(Rn), 1<p<q<, 1/p1/q=α/γ, and from the space M1,ϕ1,P(Rn)to the weak space WMq,ϕ2,P(Rn), 1q<∞, 11/q= α/γ. We alsofind conditions onϕ for the validity of the Adams type theorems MΩ,Pα,IΩ,Pα: Mp,ϕ1p,P(Rn)M

q,ϕ1q,P(Rn),1<p<q<∞.

1. Introduction

The boundedness of classical operators of the real analysis, such as the maximal operator, fractional maximal operators, fractional integral operators and singular inte- gral operators etc, from one weighted Lebesgue space to another one is well studied by now, and there are well known various applications of such results in partial differential equations. Besides Lebesgue spaces, Morrey spaces, both the classical ones (the idea of their definition having appeared in [22]) and generalized ones, also play an important role in the theory of partial differential equations, see [12,19,20,29,30].

In this paper, wefind conditions for the boundedness of the parabolic fractional maximal and integral operators with rough kernel from a parabolic generalized Morrey space to another one, including also the case of weak boundedness, and prove Adams type boundedness theorems for this operators. To precisely formulate the results of this paper, we need the notions given below.

Note that we deal not exactly with the parabolic metric, but with a general aniso- tropic metric ρ of generalized homogeneity, the parabolic metric being its particular

Mathematics subject classification(2010): 42B20, 42B25, 42B35.

Keywords and phrases: Parabolic fractional maximal function, parabolic fractional integral, parabolic generalized Morrey space.

The research of V. Guliyev was partially supported by the grant of Ahi Evran University Scientific Research Projects (PYO.FEN.4003.13.003) and (PYO.FEN.4001.13.012).

c , Zagreb

Paper JMI-09-23 257

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case, but we keep the term parabolic in the title and text of the paper, following the existing tradition, see for instance [7].

Everywhere in the sequel AB means thatACB with some positive constant Cindependent of appropriate quantities. IfABandBA, we writeA≈Band say thatA andB are equivalent.

1.1. Parabolic homogeneous space{Rn,ρ,dx}

Forx∈Rnandr>0, we denote the open ball centered atxof radiusrbyB(x,r), its complement by B(x,r)and|B(x,r)|will stand for the Lebesgue measure ofB(x,r). LetPbe a realn×nmatrix, whose all the eigenvalues have positive real part. Let At=tP (t>0), and set

γ=trP.

Then, there exists a quasi-distanceρ associated withPsuch that (see [8]) (a) ρ(Atx) =tρ(x), t>0, for every x∈Rn;

(b) ρ(0) =0, ρ(x) =ρ(−x)0

and ρ(x−y)k(ρ(x−z) +ρ(y−z));

(c) dxγ1dσ(w)dρ, where ρ=ρ(x),w=Aρ1x

anddσ(w)is a measure on the unit ellipsoid Sρ={w:ρ(w) =1}.

Then, {Rn,ρ,dx} becomes a space of homogeneous type in the sense of Coifman- Weiss (see [8]) and a homogeneous group in the sense of Folland-Stein (see [10]).

Moreover, we always assume that there hold the following properties of the quasidis- tanceρ:

(d) For every x,

c1|x|α1ρ(x)c2|x|α2, if ρ(x)1;

c3|x|α3ρ(x)c4|x|α4, if ρ(x)1 and

ρ(θx)ρ(x) for 0<θ<1,

with some positive constantsαi andci (i=1,...,4). Similar properties hold also for the quasimetricρassociated with the adjoint matrixP.

The following are some important examples of the above defined matricesP and distancesρ.

1. Let(Px,x)(x,x),x∈Rn. In this case,ρ(x)is defined as the unique solution ρ(x) =t of|At1x|=1, andk=1. This is the case studied by Calderon and Torchinsky in [7].

2. LetPbe a diagonal matrix with positive diagonal entries, andt=ρ(x),x∈Rn be the unique solution of|At1x|=1.

2a)When all the diagonal entries are greater than or equal to 1, O. V. Besov, V.

P. Il’in, P. I. Lizorkin in [3] and E. B. Fabes and N. M. Rivi`ere in [9] studied the weak (1,1)and strong(p,p)estimates of singular integral operators.

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2b)If there are diagonal entries smaller than 1, then ρ satisfies the above(a) (d)withk>1.

3. In [28] Stein and Wainger defined and studied some problems in harmonic analysis on this kind of spaces. Consider a one parameter group of dilations onRn, At:RnRn for eacht>0 with the following properties:

(i) Ast=AsAt and A1 is the identity;

(ii) lim

t→0Atx=0 for every x∈Rn; (iii) Atx=tPx=exp{Plogt}x.

Then all eigenvalues of P have positive real part. Then in this case there exist 0<β1<β2 and 0<c1<c2 such thatAt has the following properties:

(iv) for everyx

c1tβ1|x|<|Atx|<c2tβ2|x|, fort1 and

(c2)1tβ2|x|<|Atx|<(c1)1tβ1|x|, for t1.

By [28], if|Atx|were strictly monotonic, then we might define the unique solutions of|Atx|=1 byρ(x). Otherwise, there is a positive definite symmetric matrixB such that

Atx=AtxB= (BAtx,Atx)12

is strictly increasing and thus ρ can be defined as follows: For x =0, ρ(x) is the unique positivet such thatAt1(x)=1. Forx=0, setρ(x) =0. Then for x =0

x=Aρ(x)w(x),

wherew(x)=1 andw(x)is unique. Let ρ(ξ)be the quasi-distance function corre- sponding to the groupAt=tP=exp(Plogt). Thenξ =Aρ(ξ)(w(ξ))where

w(ξ)= (B1w(ξ),w(ξ))12 for an appropriate positive definite symmetric matrix B.

It was pointed out in [28] that both ρ and ρ satisfy (1.1)–(1.4), and one can easily see thatα14=β1213=β11, andcidepends on on the matrices Pand B. Moreover, in this case

dxγ1dσ(w)dρ,

wheredσ(w)is aC measure on the ellipsoidρ(w)2= (Bw,w) =1.

In the standard parabolic caseP0=diag(1,...,1,2)we have

ρ(x) =

|x|2+

|x|4+x2n

2 , x= (x,xn).

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The balls E(x,r) ={y∈Rn:ρ(x−y)<r} with respect to the quasidistance ρ are ellipsoids. For its Lebesgue measure one has

|E(x,r)|=vρrγ,

wherevρ is the volume of the unit ellipsoid. By E(x,r) =Rn\E(x,r)we denote the complement ofE(x,r).

1.2. Parabolic generalized Morrey spaces

We define the parabolic Morrey spaceMp,λ,P(Rn)via the norm

fMp,λ,P = sup

x∈Rn,t>0

tλ

E(x,t)|f(y)|pdy 1/p

<, where 1p∞and 0λ γ.

If λ =0, then Mp,0,P(Rn) =Lp(Rn); if λ =γ, then Mp,γ,P(Rn) =L(Rn); if λ<0 or λ>γ, thenMp,λ,P=Θ, whereΘ is the set of all functions equivalent to 0 onRn.

We also denote by WMp,λ,P(Rn) the weak parabolic Morrey space of functions f∈W Llocp (Rn)for which

fWMp,λ,P= sup

x∈Rn,t>0rλpfW Lp(E(x,r))<,

whereW Lp(E(x,r))denotes the weak Lp-space of measurable functions f for which fWLp(E(x,r))=sup

t>0t|{y∈E(x,r):|f(y)|>t}|1/p. Note thatW Lp(Rn) =WMp,0,P(Rn),

Mp,λ,P(Rn)⊂WMp,λ,P(Rn) and fWMp,λ,PfMp,λ,P. If P=I, then Mp,λ(Rn)≡Mp,λ,I(Rn)is the classical Morrey space.

We introduce the parabolic generalized Morrey spaces following the known ideas of defining generalized Morrey spaces ([15,24,26] etc).

DEFINITION1.1. Let ϕ(x,r) be a positive measurable function on Rn×(0,∞) and 1p<∞. The space Mp,ϕ,P≡Mp,ϕ,P(Rn), called the parabolic generalized Morrey space, is defined by the norm

fMp,ϕ,P = sup

x∈Rn,t>0ϕ(x,t)1|E(x,t)|1pfLp(E(x,t)).

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DEFINITION1.2. Let ϕ(x,r) be a positive measurable function on Rn×(0,∞) and 1p<∞. The space WMp,ϕ,P≡WMp,ϕ,P(Rn), called the weak parabolic generalized Morrey space, is defined by the norm

fWMp,ϕ,P = sup

x∈Rn,t>0ϕ(x,t)1|E(x,t)|1pfW Lp(E(x,t)).

IfP=I, thenMp,ϕ(Rn)≡Mp,ϕ,I(Rn)andWMp,ϕ(Rn)≡WMp,ϕ,I(Rn)are the generalized Morrey space and the weak generalized Morrey space, respectively.

According to this definition, we recover the space Mp,λ,P(Rn) under the choice ϕ(x,r) =rλpγ:

Mp,λ,P(Rn) =Mp,ϕ,P(Rn)

ϕ(x,r)=rλpγ

.

1.3. Operators under consideration

Let Sρ ={w∈Rn:ρ(w) =1} be the unit ρ-sphere (ellipsoid) in Rn (n2) equipped with the normalized Lebesgue surface measure dσ and Ω be At-homoge- neous of degree zero, i.e. Ω(Atx)Ω(x), x∈Rn, t >0. The parabolic fractional maximal function MΩ,αP f and the parabolic fractional integral IΩ,αP f by with rough kernels, 0<α<γ,of a function f∈Lloc1 (Rn)are defined by

MΩ,αP f(x) =sup

t>0|E(x,t)|1+αγ

E(x,t)|Ω(x−y)| |f(y)|dy,

IΩ,αP f(x) =

Rn

Ω(x−y) f(y) ρ(x−y)γα dy.

If Ω1, then MαP≡M1,αP and IαP≡I1,αP are the parabolic fractional maximal operator and the parabolic fractional integral operator, respectively. If α =0, then MΩP≡MΩ,0P is the parabolic maximal operator with rough kernel. IfP=I, thenMΩ,α MΩ,αI is the fractional maximal operator with rough kernel, andM≡MΩ,0I is the Hardy- Littlewood maximal operator with rough kernel. It is well known that the parabolic fractional maximal operators play an important role in harmonic analysis (see [10,27]).

We prove the boundedness of the parabolic fractional maximal and integral op- erators MΩ,αP , IΩ,αP with rough kernel from one parabolic generalized Morrey space Mp,ϕ1,P(Rn) to another one Mq,ϕ2,P(Rn), 1<p<q<∞, 1/p−1/q/γ, and from the spaceM1,ϕ1,P(Rn)to the weak spaceWMq,ϕ2,P(Rn), 1q<∞, 11/q= α/γ. We also prove the Adams type boundedness of the operators MΩ,αP , IΩ,αP from Mp,ϕ1p,P(Rn) to M

q,ϕ1q,P(Rn) for 1 < p < q < ∞ and from M1,ϕ,P(Rn) to WM

q,ϕ1q,P(Rn)for 1<q<∞.

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2. Preliminaries

In the papers [24, 25], where the maximal and other operator were studied in generalized Morrey spaces, the following condition was imposed onϕ(x,r):

c1ϕ(x,r)ϕ(x,t)cϕ(x,r), (2.1) wheneverrt2r, jointly with the condition:

r ϕ(x,t)pdt

t Cϕ(x,r)p for the maximal or singular operators and the condition

r tαpϕ(x,t)pdt

t C rαpϕ(x,r)p (2.2) for potential and fractional maximal operators, wherecandCdo not depend on rand x.

The results of [24,25] imply the following statement.

THEOREM2.1. Let 1p <, 0<α < γp, 1q = 1pαγ and ϕ(x,t) satisfy the conditions(2.1)and (2.2). Then MαP and IαP are bounded from Mp,ϕ,P(Rn) to Mq,ϕ,P(Rn)for p>1 and fromM1,ϕ,P(Rn)to WMq,ϕ,P(Rn)for p=1.

In [11] the following statement was proved by fractional integral operator with rough kernelsIΩ,α, containing the result in [21,24].

THEOREM2.2. LetΩ∈Ls(Sn−1), 1<s, be homogeneous of degree zero.

Let0<α<n, s<p<αn, 1q=1pαn andϕ(x,r)satisfy the condition(2.1)and

r tαpϕ(x,t)pdt

t C rαpϕ(x,r)p, (2.3) where C does not depend on x and r . Then the operator IΩ,α is bounded from Mp,ϕ to Mq,ϕ.

The following statements, containing results obtained in [21], [24] was proved in [13,15] (see also [4]–[6], [14]–[17]).

THEOREM2.3. Let0<α<γ,1p<αγ, 1q= 1pαγ and1,ϕ2)satisfy the

condition

r tα1ϕ1(x,t)dtCϕ2(x,r), (2.4) where C does not depend on x and r . Then the operator IαP is bounded from Mp,ϕ1,P to Mq,ϕ2,P for p>1 and from M1,ϕ1,Pto W LMq,ϕ2 for p=1.

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Let v be a weight on (0,∞). We denote by L,v(0,∞) the space of all functions g(t),t>0 withfinite norm

gL,v(0,∞)=ess sup

t>0 v(t)|g(t)|

and writeL(0,∞)≡L,1(0,∞). Let M(0,∞) be the set of all Lebesgue-measurable functions on (0,∞) and M+(0,∞) its subset of all nonnegative functions. By M+(0,∞;)we denote the cone of all functions inM+(0,∞)non-decreasing on(0,∞) and introduce also the set

A=

ϕM+(0,∞;): lim

t→0+ϕ(t) =0 .

Letube a non-negative continuous function on (0,∞). We define the supremal opera- torSuon g∈M(0,∞)by

(Sug)(t):=u gL(t,∞), t∈(0,∞).

The following theorem was proved in [5].

THEOREM2.4. Let v1, v2 be non-negative measurable functions satisfying 0<

v1L(t,∞) <for any t>0 and let u be a continuous non-negative function on (0,∞).Then the operator Suis bounded from L,v1(0,∞)to L,v2(0,∞)on the coneA if and only if

v2Su

v11L(·,∞)

L(0,∞)<. (2.5)

We are going to use the following statement on the boundedness of the weighted Hardy operator

Hwg(t):=

t g(s)w(s)ds, 0<t<, wherewis afixed function non-negative and measurable on(0,∞).

The following theorem was proved in [18].

THEOREM2.5. Let v1, v2and w be positive almost everywhere and measurable functions on(0,∞). The inequality

ess sup

t>0 v2(t)Hwg(t)Cess sup

t>0 v1(t)g(t) (2.6)

holds for some C>0 for all non-negative and non-decreasing g on(0,∞) if and only if

B:=ess sup

t>0 v2(t)

t

w(s)ds ess sup

s<τ<v1(τ)<. (2.7) Moreover, if Cis the minimal value of C in(2.6), then C=B.

REMARK2.1. In (2.6) and (2.7) it is assumed that 1 =0 and 0·∞=0.

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3. Boundedness of the parabolic fractional operators in the spacesLp(Rn)

In this section we prove the (p,p)-boundedness of the operator MΩP and the (p,q)-boundedness of the operatorsIΩ,αP andMΩ,αP .

THEOREM3.1. LetΩ∈Ls(Sρ),1<s, be At-homogeneous of degree zero.

Then the operator MΩP is bounded in the space Lp(Rn), p>s.

Proof. In the cases=∞the statement of Theorem3.1is known and may be found in [8] and [27]. So we assume that 1<s<∞.

Note that

Ω(x− ·)Ls(E(x,t))=

E(0,t)|Ω(y)|sdy1/s

= t 0rγ1dr

Sρ|Ω(ω)|sdσ(ω)1/s

(3.1)

=c0ΩLs(Sρ)|E(x,t)|1/s, wherec0=

γvρ1/s

andvρ=|E(0,1)|.

The case p=∞is easy. Indeed, making use of (3.1), we get MΩPfLfLsup

t>0|E(x,t)|1+s1Ω(x− ·)Ls(E(x,t))c0ΩLs(Sρ)fL. So we assume thats<p<.Applying H¨older’s inequality, we get

MΩPf(x)sup

t>0|E(x,t)|1Ω(x− ·)Ls(E(x,t))fLs(E(x,t)). (3.2) Then from (3.2) and (3.1) we have

MΩPf(x)c0ΩLs(Sρ)sup

t>0|E(x,t)|1+1/sfLs(E(x,t))

=c0ΩLs(Sρ)

sup

t>0|E(x,t)|1|f|sL1(E(x,t))

1/s

=c0ΩLs(Sρ)

MP(|f|s)(x)1/s

. (3.3)

Therefore, from (3.3) for 1s<p<∞we get MΩPfLpc0ΩLs(Sρ)

MP(|f|s)(x)1/s Lp

=c0ΩLs(Sρ)MP|f|s1/sLp

/s |f|s1/sLp

/s =fLp.

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THEOREM3.2. Suppose that 0<α<γ and the function Ω∈L γ

γα(Sρ), is At- homogeneous of degree zero. Let1p<αγ and1/p−1/q/γ. Then the fractional integral operator IΩ,αP is bounded from Lp(Rn)to Lq(Rn)for p>1and from L1(Rn) to W Lq(Rn)for p=1.

Proof. We denote

K(x):= Ω(x) ρ(x)γα for brevity, and may assume thatK(x)0. We have

{x∈Rn:IαPf(x)>λ}{x∈Rn:IΩPf(x)>Cγ,α1λ}I1+I2,

where I1:=

x∈Rn:|K1μ∗f(x)|>λ

2, I2:=

x∈Rn:|Kμ2∗f(x)|>λ 2, Kμ1(x) = (K(x)μ)χE(μ)(x) and Kμ2(x) =K(x)−Kμ1(x), μ>0 and E(μ) ={x∈Rn:K(x)>μ}. Note that

|E(μ)|Bμγγα. (3.4)

whereB=α1ΩLγγαγ

γα(Sρ) as seen from the following estimation:

|E(μ)| 1 μ

E(μ)

|Ω(x)|

ρ(x)γαdx

= 1 μ

SρΩ(x)dσ(x) |Ω(x)|

μ

γ1α

0 rα1dr=Bμγγα. By means of (3.4) we can prove the estimate

Kμ2Lp γα γ Bq

p1

μ(γγα)q, 1p< γ α. Forp=1 it easily follows from (3.4), and for p>1 we have

Rn|Kμ2(x)|pdx=p

μ

0 tp1|E(t)|dt pB μ

0 tp1γγαdt

α

γ Bqμγγαpq.

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Then by the Young inequality we obtain Kμ2∗fLKμ2LpfLpγα

γ Bq p1

μ(γγα)q fLp. Now for a λ>0, we choose μ such that

γα γ Bq

p1

μ(γγα)q fLp =λ 2, then

x∈Rn:|Kμ2∗f(x)|>λ 2=0. Thus

{x∈Rn:IαPf(x)>λ}

x∈Rn:|Kμ1∗f(x)|>λ 2

2

λ Kμ1fLp p

. (3.5)

The following estimations take (3.4) into account:

Rn|Kμ1(x)|dx=

E(μ)

|K(x)| −μdx

0 |E(t+μ)|dt

B

μ tγγαdt (3.6)

= αB

γα μγαα. For all f ∈L(Rn)andx∈Rn, from (3.6) it follows that

|K1μ∗f(x)|fL

Rn|K1μ(x)|dx αB

γα μγαα fL. (3.7) For all f ∈L1(Rn), from (3.6) follows

Kμ1∗fL1

Rn

Rn|Kμ1(x−y)||f(y)|dxdy αB

γα μγαα fL1. (3.8) Thus from (3.7) and (3.8) follows that the operatorT1:f→Kμ1∗f is of(∞,∞)and (1,1)-type. Then by the Riesz-Thorin theorem the operator T1 is also of (p,p)-type, 1<p<∞, and

T1fLp αB

γα μγαα fLp. (3.9)

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From (3.5) and (3.9) we get

{x∈Rn:IαPf(x)>λ}2

λ K1μfLp p

C1

λ fLp q

, (3.10)

whereCis independent ofλ and f.

To finish the proof, i.e. prove that the operator IαP is bounded from Lp(Rn) to Lq(Rn) for 1<p<αγ and 1/p−1/q/γ, observe that the inequality (3.10) tells us thatIαP is bounded fromL1(Rn)toW Lq(Rn)with 11/q/γ. We choose any p0 such that p<p0<αγ, and put q10 = p10αγ. By (3.10) the operatorIαP is of weak (p0,q0)-type. Since it is also of weak(1,q)-type by the Marcinkiewicz interpolation theorem, we conclude thatIαP is of(p,q)-type.

COROLLARY3.1. Under the assumptions of Theorem3.2, the fractional maximal operator MΩ,αP is bounded from Lp(Rn) to Lq(Rn) for p>1 and from L1(Rn) to W Lq(Rn)for p=1.

Proof. It suffices to refer to the known fact that

MΩ,αP f(x)Cγ,αIΩ,αP f(x), Cγ,α=|E(0,1)|γγα, Note that in the isotropic case P=I Theorem3.2was proved in [23].

4. Parabolic fractional maximal operator with rough kernels in the spaces Mp,ϕ,P(Rn)

Note that in the next Section 5 we obtain boundedness results of Spanne and Adams type for the fractional integral operator IΩ,αP . Although MPΩ,αf is dominated byIΩ,αP f and consequently from the results of Section5there may be derived the cor- responding results forMΩ,αP f, we obtain here a Spanne type statement for the operator MΩ,αP f separately from Section5, because for this operator we are able to obtain the boundedness results under weaker assumptions than in Section5, see Remark5.3.

Recall that in the classical isotropic case, i.e. in the case of of the operator Mα, 0α<nonRnwith Euclidean distance, sufficient conditions on for the boundedness of this operator in generalized Morrey spacesMp,ϕ(Rn) have been obtained in [2,5, 15,24].

LEMMA4.1. Suppose that 0<α <γ and the function Ω∈L γ

γα(Sρ) is At- homogeneous of degree zero. Let1p<αγ, 1q=1pαγ. Then for any ballE =E(x,r) inRn and f∈Llocp (Rn)there hold the inequalities

MΩ,αP fLq(E(x,r))fLp(E(x,2kr))+rγq sup

t>2krtγ+αΩ(x− ·)f(·)L1(E(x,t)), p>1,

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MΩ,αP fW Lq(E(x,r))fL1(E(x,2kr))+rγq sup

t>2krtγ+αΩ(x− ·)f(·)L1(E(x,t)), p=1. (4.1) Proof. Given a ball E =E(x,r), we split the function f as f = f1+f2, where f1=fχE(x,2kr) and f2=fχ(E(x,2kr)),and then

MPΩ,αfLq(E)MPΩ,αf1Lq(E)+MΩ,αP f2Lq(E). Let p>1.By Corollary3.1

MΩ,αP f1Lq(E)fLp(E(x,2kr)).

To estimateMΩ,αP f2(y), observe that ifE(y,t)(E(x,2kr)) =/0, wherey∈E, then t>r. Indeed, if z∈E(y,t)(E(x,2kr)),thent>ρ(y−z)1kρ(x−z)ρ(x−y)>

2r−r=r.

On the other hand, E(y,t)(E(x,2kr))⊂E(x,2kt). Indeed, for z∈E(y,t)

(E(x,2kr))we getρ(x−z)kρ(y−z) +kρ(x−y)<k(t+r)<2kt.

Hence

MΩ,αP f2(y) =sup

t>0

1

|E(y,t)|1α/γ

E(y,t)(E(x,2kr))|f(z)||Ω(x−z)|dz (2k)γαsup

t>r

1

|E(x,2kt)|1α/γ

E(x,2kt)|f(z)||Ω(x−z)|dz

= (2k)γα sup

t>2kr

1

|E(x,t)|1α/γ

E(x,t)|f(z)||Ω(x−z)|dz. Therefore, for ally∈E we have

MΩ,αP f2(y)(2k)γα sup

t>2kr

1

|E(x,t)|1α/γ

E(x,t)|f(z)||Ω(x−z)|dz. (4.2) Thus

MΩ,αP fLq(E)fLp(E(x,2kr))+|E|1q sup

t>2kr

1

|E(x,t)|1α/γ

E(x,t)|f(z)||Ω(x−z)|dz. Let p=1. We have

MΩ,αP fW Lq(E)MΩ,αP f1WLq(E)+MΩ,αP f2W Lq(E). By Corollary3.1we get

MΩ,αP f1WLq(E)fL1(E(x,2kr)). Then by (4.2) we arrive at (4.1) and complete the proof.

Similarly to Lemma4.1and Theorem3.1the following lemma may be proved.

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LEMMA4.2. Let the function Ω∈Ls(Sρ), 1<s, be At-homogeneous of degree zero. Then for p>s and any ballE =E(x,r)the inequality

MΩPfLp(E(x,r))fLp(E(x,2kr))+rγp sup

t>2krtγΩ(x− ·)f(·)L1(E(x,t)) holds for all f∈Lloc1 (Rn).

LEMMA4.3. Suppose that the functionΩ∈L γ

γα(Sρ)is At-homogeneous of de- gree zero. Let0<α<γ, 1p<αγ, 1q=1pαγ. Then for f ∈Llocp (Rn) there hold the inequalities

MΩ,αP fLq(E(x,r))rγq sup

t>2krtγqfLp(E(x,t)), p>1, (4.3) MΩ,αP fWLq(E(x,r))rγq sup

t>2krtγqfL1(E(x,t)), p=1. (4.4) Proof. Let p>1 Denote

A1:=|E|1q

t>2krsup 1

|E(x,t)|1α/γ

E(x,t)|f(z)||Ω(x−z)|dz

, A2:=fLp(E(x,2kr)).

Applying H¨older’s inequality, we get A1|E|1q sup

t>2krfLp(E(x,t))Ω(x− ·)L γ

γα(E(x,t))|E(x,t)|αγ1p |E|1q sup

t>2kr|E(x,t)|1qfLp(E(x,t)). On the other hand,

|E|1q sup

t>2kr|E(x,t)|1qfLp(E(x,t))

|E|1q sup

t>2kr|E(x,t)|1qfLp(E(x,2kr))A2. SinceMPΩ,αfLq(E)A1+A2, by Lemma4.1, we arrive at (4.3).

Let p=1. The inequality (4.4) directly follows from (4.1).

Similarly to Lemma4.3and Theorem3.1the following lemma is also proved.

LEMMA4.4. Suppose that the functionΩ∈Ls(Sρ), 1<s, is At-homoge- neous of degree zero. Then for p>s and any ballE =E(x,r), the inequality

MPΩfLp(E(x,r))rγq sup

t>2krtγpfLp(E(x,t))

holds for f∈Llocp (Rn).

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THEOREM4.1. Suppose that0<α <γ and the functionΩ∈L γ

γα(Sρ) is At- homogeneous of degree zero. Let 1p< αγ, 1q= 1pαγ, and1,ϕ2) satisfy the condition

r<t<sup tαγp ess inf

t<τ<ϕ1(x,τ)τγp Cϕ2(x,r), (4.5) where C does not depend on x and r . Then the operator MΩ,αP is bounded from Mp,ϕ1,P(Rn) to Mq,ϕ2,P(Rn)for p>1 and from M1,ϕ1,P(Rn)to WMq,ϕ2,P(Rn) for p=1.

Proof. By Theorem2.4and Lemma4.3we get MΩ,αP fMq,ϕ2,P sup

x∈Rn,r>0ϕ2(x,r)1sup

t>rtγqfLp(E(x,t))

sup

x∈Rn,r>0ϕ1(x,r)1rγpfLp(E(x,r))=fMp<

Referanslar

Benzer Belgeler