doi:10.4236/apm.2011.16060 Published Online November 2011 (http://www.SciRP.org/journal/apm)
A Class of Singular Integral Operators Associated to
Surfaces of Revolution
*
Muliang Cao1, Huoxiong Wu2#
1Guangzhou Branch of Institute of Electronic Technology, PLA Information Engineering University,
Guangzhou, China
2School of Mathematical Sciences, Xiamen University, Fujian, China
E-mail: ml_cao@163.com,#[email protected]
Received July 19, 2011; revised August 10, 2011; accepted August 20, 2011
Abstract
In this paper, the authors establish the Lp-mapping properties of a class of singular integral operators along surfaces of revolution with rough kernels. The size condition on the kernels is optimal and much weaker than that for the classical Calderon-Zygmund singular integral operators.
Keywords:Singular Integrals, Surface of Revolution, Maximal Operator, Rough Kernel
1. Introduction and Main Results
Let , , be the n-dimensional Euclidean space and be the unit sphere in equipped with the normalized Lebesgue measure Let
n
R
n
S
2
n
1 Rn
d d
.
, ; n
y y y R
n
be the surface of revolution generated by a suitable function . For
nonzero points
: 0, R x R , we denote x'x x. Let be a homogeneous function of degree zero on
and satisfyn1
L S1n
R
1 d
n
S y y
0, (1.1) Suppose that is a radial measurable function. De-fine the singular integral operatorh
,h
T in Rn1 along
by
, 1
1
,
. . , d
| | n
h n
n n
R
T f x x
h y y
p v f x y x y y
y
(1.2)for all fn1 (the Schwartz function class on Rn1),
where
, n1
1
n n
x x R R R .
Operators of the type (1.2) have been studied quite extensively (see [1-13] and therein numerous references). We refer the readers to see Stein-Wainger’s report [14, 15] for more background information. In 1996, Kim, Wainger, Wright and Ziesler proved the following result.
Theorem A [10]. Let be convex,
in-creasing and
2 0,
C
0 0 . Suppose that C
Sn1 nR
is a homogeneous function of degree zero on and sat-isfies (1.1). Then T,1 is bounded on L Rp
n1 for1 p .
By a minor modification of the proof in Theorem A, one can show that the conclusion of Theorem A remains valid if the condition is replaced by the
condition
1
n C S
1q n L S
for some (see [16, pp. 372-373], as well as [6]). Subsequently, this result was improved and extended by many authors (see [1,2,5,6, 11,12] et al.). In particular, in 2001, Lu, Pan and Yang gave the general theorem as follows.
1
R q
Theorem B [11]. Let be a
continu-ously differentiable on
: 0,
0,
and satisfy
t 0 Ct for some and small , where is a constant independent of . Suppose that
t
C t
11 n
H S
and h L
0,
. Then,h T is bounded on L Rp
n1 for 1 , provided that themaximal operator
p
defined by
2 12 1 p
2
j j
j
, s
j
u
,
df r s
f r
t s t t
is bounded on L Rp
2 for p1.
h L
Actually, the condition can be
weak-ened to the case:
0,
1
0 0 { ;
s
h sup s
h R s h
t dt }, 1
with 1 p1 2 min
1 2,1
(see [9]), and the size condition on in Theorem B is the best one, so far,
even if
t 0 (see [8]).
t
On the other hand, for , it is known in [17], if , that
2 , 1
h L R r dr ,h
T
0 is bounded on L Rp
n1
S 1
for , provided , which
is optimal and much weaker than that for the classical Calderon-Zygmund singular integral operators. It should be noted that the spaces and
do not include in each other. 1
1 n
H S
p
1
2 R r dr, 1 n
R
1/ 2log
L L
1/ 2log
L L
1/ 2 1log n
L L S
n
Inspired by Al-Salman’s work [17], we shall establish the following main result in this paper.
Theorem 1. Let be a suitable
func-tion, which ensures that the integral in (1.2) exists in principle-value sense when, say, (the Schwartz function class on ). Suppose that
, is a homogenous function of de- gree zero on and satisfies (1.1). If
, then
: 0, R
f
1
n
Sn1
1
n
R
h L
1) T,h f 2
n1 L R2
n1.L R C f 2) T,h
f L Rp
n1 C f L Rp
n1,for provided that the lower dimensional maximal operator
1 p ,
M defined by
1
/ 2 0
, sup R , d
R R
M f r s R f r t s t t
(1.3)is bounded on L Rp
2
for 1 p .In Theorem 1, if
t is continuously differentiable on
0,
and satisfy
t 0 Ct for some and small , where is a constant independent of , in particular, if , then the integral in (1.2) exists in principle-value sense when, say,t C
t1
n
1 0,1
t C
f
(the Schwartz function class on Rn1) (see [11]).
2Remark 1. The L Rp boundedness of M is known for many
t ’s. A few prominent examples are as follows:1) If
t is a real-valued polynomial, then M is bounded on L Rp
2 for , see [16, p. 477] or [15].
t t
1 p
2) If with
0,1
, then M is bounded on L Rp
2 for , see [13].
t C1
p13) If
0,1
such that
0
0 0 0 tand
t is a convex increasing function for , M is bounded on for , see [13], see [7, Corollary 5.3].
2
p
L R
p14) Let b t
t
t t . If
t C2
0,1
,
t is convex on
with , andthere exists an
0,0
0 0 0
so that for each t0,
,b t b t t then M is bounded on L Rp
2 for, see [4, Theorem 1.5]. In particular, if 1
p
t isether even or odd and there exists a so that for each
0 C
0,
t
Ct 2
t , then M is bounded on L Rp
2 for p1, see [3] or [4].In order to obtain Theorem 1, we let S, be the op-erator defined by
1
, 1
1/ 2 2 1
0 ,
d
: n ', d
n
n S
S f x x
r
y f x ry x y y
r
.Clearly, if h L R r dr 2
, 1
, then
2
1
,h , n1 L R r dr, , , n T f x x h S f x x1 . Therefore Theorem 1 can be deduced immediately from the next theorem.
Theorem 2. Let and be as in Theorem 1. Then
1) S,
f L R2
n1 C f L R2
n1.2) S,
f L Rp
n1 C f L Rp
n1,2 p , provided that the maximal operator M
in (1.3) is bounded on L R for p
2 1 p .Remark 2. By the similar arguments as in [1], we
re-mark that the condition is
op-timal. Precisely, there exists an lies in for all
1/ 2 1log n
L L S
log
n1L L S
1 2 and satisfies (1.1) such that S, is unbounded on . And it is worth pointing out that the size condition is much weaker than that for the classical Calderón-Zygmund singular integral operators.
1p n L R
This paper is organize as follows. In Section 2 we will give the proofs of our theorems. An extension of our main results will be given in Section 3. We would like to remark that the main ideas in the proofs of our results are taken from [7,9,17].
Throughout this paper, we always use letter to denote positive constants that may vary at each occur-rence but are independent of the essential variables.
C
2. Proofs of Main Results
Let us begin with a lemma, which will play a key role in the proofs of our main results.
Lemma 2.1. Let and satisfy (1.1). If
the maximal operator
1 n1
L S
M in (1.3) is bounded on
2p
L R for, then the following maximal operator M,
defined by
, 1
1 0 / 2 | |
,
: sup , d
n
n n
R R y R
M f x x y
f x y x y y
y
(2.1)is bounded on L Rp
n1 with bound
1 1 , 1 .
Proof. Since
1
1
1
, 1
1 / 2
0
1 / 2
0
, ' 1
,
d
sup , d
d
| sup ', d
, d
n
n
n
n R
n R S
R
R
n
S R R
y n
S
M f x x
r
y f x ry x r y
r r
y f x ry x r
r
y M f x x y
y
where
2
, ' 1 1
0
1
, : sup R , d
y n R n
R .
M f x x f x ry x r r
R
Thus by Minkowski's inequality, we have
1 1
1
, L Rp n Sn , 'y L Rp n d .
M f
y M f yIt remains to show that
1
1,y L Rp n L Rp n
M f C f
with C independent of .
1
y
n1.Let
1,0, ,0 S For each fixed y'Sn1,choose a rotation such that y 1. Denote the
in-verse of by 1 and define the function f by . Then
,xn1
f
x x, n1
f x
, n 1
1
, n 1
f x ry x r f x r x 1 r . This together with the Lp-bondedness of M
, and change of variables, show that
1
1,y L Rp n L Rp n , 1 ,
M f C f p
where C is independent of. Lemma 2.1 is proved. Next we introduce some notations. Assume that and satisfies (1.1). For any
1/ 2 1log n
L L S
l, let
n1: 2l
2l 1
l
E yS y Also,
we let
1
Set0 : | | 2
n
E yS y
: 4l
l D l E 2
and for l1,
1
1 1 :
d ,
l
n l
n
l E
E S
y y y S
y y y
and 0
y :
y
l D l
y. 0,
Then we have the following:
1 d 0,
n l
S y y l
(2.2)1 2 l 1: 2 ,
l E A l Dl ,
(2.3)
0 1 C 0 2 C ,
(2.4)
y l D {0} l
y ,
(2.5)
1/ 2
1/2 1{0} 1 l log n ,
l D l A C L L S
(2.6)where
1
l
l E
A for l D and A01.
Now we give the proofs of our theorems as follows. Proof of Theorem 2. For each l D
0 , we let
1
, 1
1 2 2 1
0
, :
d
, d
l
n n
l n
S
S f x x
r
y f x ry x y y
r
.By (2.5) and Minkowski's inequality, we have
, , n1 l D {0} l, , n
S f x x
S f x x1
. (2.7) For any l D
0 , let’s argue as in the proof of Theorem 2.1 in [1], choose a collection of C function
l j, j on
0,
with the following properties:supp
1 1 1 1, 2 , 2
j l j l l j
,
(2.8)
,
0l j t 1, and
(2.9)2
, 1,
l j j t
, d
, d
l j t C
t t
(2.10)
where t0, , and C is a constant independ-ent of l.
For each j and l D
0 , denote bythe multiplier l j,
S
, , 1 , ,
l j n l j n
S f f 1 , and 2 by
,
l j
S
2
, , 1 , , ,
l j n l j l j n
S f x x S S f x x1 .
Then by (2.9) and Minkowski’s inequality,
1 1
1 1
1 1
, 1
2 2
1 2 2 2
, 1
2 1
1/ 2 2 2
, 1
, 1
,
d
, d
d
( ', )d
: , ,
l
j l
j l n
l n n
l
j k S
l j k n
l
k j S
l j k n
l k n
k
S f x x
y
r
S f x ry x r y
r y
r
S f x ry x r y
r
I f x x
1 1
2
, 1 1
1/ 2 2 2
, 1
,
d
', d .
l n
l k n j S l
l j k n
I f x x y
r
S f x ry x r y
r
This together with (2.7) implies
1
1, L Rp n l D 0 k l k, L Rp n .
S f
I f (2.11)Now we estimate Il k,
f L Rp
n1
in the followingcases:
Case 1. For p2, we claim that there exists 0
such that for l D
0
,
2
1
2
11/ 2 | |
, n 2 1 n
k
l k L R l L R
I f C l A f , (2.12)
where C is independent of l and k.
Indeed, by Plancheral’s theorem and Fubini’s theorem,
,
2 2
, 2 , 1 , d d 1,
l j k
l k j n l j n
I f f J
(2.13) where
1 1 1
R, : : 2 2 ,
j k l l j k l n
l j k R
1 1
1
2
2 2 '
, 1
d
e d
l j l
n
i ry
l j S l
r
J y
r
yIn order to prove (2.12), we first estimate Jl j,
.Obviously, we have
2
2, 1 1 1
l j l l .
J l C l A (2.14)
By (2.2), a straightforward computing shows that
2 2 1 1
, 1
2 1 1 2
1 2
1 2 ,
j l
l j l
j l
l
J l
C l A
(2.15)
Using interpolation between (2.14) and (2.15), we get
2 1 1 2/ 1, 1 2
l j l
l j l
J C l A . (2.16)
On the other hand, we have
1
1 1 1
1 1 1 1
2
, 1
2
2 2 1
d e d d
d
e d d
l
n n
j l
n n l j l
l j S S l l
i r y u
l l
S S
i r y u
J y u
r
y u
r
y u
r y u
r
.
And by integration by parts,
1 1
2 2 1
1 1
d e
1 2
l j l
i r y u
j l
r r
C l y u
,
with the easy fact
1 1
2 2 1
d
e 1
l i j l r y u r
l r
,we obtain
1 1
2 2 1
1/ 4 1
d e
1 2
l j l
i r y u
j l
r r
C l y u
.
Thus, by Holder’s inequality
1 1
1/ 4 2
1
, 2
1/ 2 1/ 2
1/ 4 2
1
2
1 2
1 2 .
n n
j l
l j l
S S j l
l
J C l
y u d y d u
C l
Note that 0 2 C CA0, and for l D ,
32l l
l l
A C E C2 , we have
1/ 2 2 1 12 2 2
l l
l C El C
.
l A
Consequently,
4 1 1 1/ 4 2, 1 2 2
l j l
l j l
J C l A .
This together with (2.14) and an interpolation implies
2 1 1 4 1, 1 2
l j l
l j l
J C l A . (2.17)
Then by the fact that l j k, l j k, ' whenever
1, , 1 ,
j j j j (2.12) follows from (2.13), (2.16) and (2.17).
Case 2. For p2, we shall show that there exists
0
such that for l D
0 ,
1
11/ 2 | |
, p n 2 1 p n
k
l k L R l L R
I f C l A f
.
(2.18)
where C is independent of l and k.
Indeed, choose g L p/ 2
Rn1 such that p/2
n1 1L R
g and
1
2l
1 1 1
2
, 1
2
1 1
2
, 1
1 1
2 ', 2 d
d
, d d .
p n n n
l k L R R j S l
j l j l
l j k n
n n
I f y
S f x ry x r y
r
g x x x x r
1
1 1
2 2
, 1
1 1
1 2 2
, 1 1 1
sup
d
2 , 2 d
, d d .
l
n n
l k p R j S l
j l j l
n
l j k n n l
j
I f y
r
g x ry x r y
r
S f x x x x
Note that
1 1
2 1
1 ( 1)
1
, 1
sup
d
2 , 2 d
1 , .
l n
l
j S l
j l j l
n
n
y
r
g x ry x r y
r l M g x x
Applying Holder’s inequality again, it follows from Lemma 2.1 and the Littlewood-Paley theory (see [18, Chapter 4]) that
2 2
, 1 / 2
1/ 2 2 2
,
1/ 2 2
2 2
, 1
2 2 2 2
1
1
1
1 1
l k p l p
l j k j
p l j l j k
.
p
l p l p
I f C l g
S f
C l S f
C l f C l A f
This together with (2.12) and an interpolation implies (2.18).
Therefore, by (2.11), (2.12) and (2.6), we get
2 1 2 1
2 1 1/2 1 2 1
1/ 2
, {0}
| |
1/ 2 0
log
1
2
1
.
n
n
n
n n
l D k L R
k
l L R
l
l D L R
L L S L R
S f C l
A f
C l A f
C f
This prove 1) of Theorem 2.
If M is bounded on L Rp
2 for 1 , thenby (2.11), (2.18) and (2.6), we obtain that for ,
p
2
p
1/2 1
11
, L Rp n Llog L Sn L Rp n ,
S f C f
which completes the proof of Theorem 2. Proof of Theorem 1. By the fact
2
1
,h , n1 L R r dr, , , n1
T f x x h S f x x , and Theorem 2, it follows that T,h is bounded on
for . On the other hand, by duality we can obtain that T,h
1p n L R
3. Further Results
In this section, we will extend the definition of T,h to
higher dimensional cases. Let Φ(t)=(1(t), ···, m(t)) be a curve on Rm, , where each
i(t) is a real-valued continuous function. For m2 x, yRn, and x*Rm, we define
, , * . .
, * d .
n
n
h R
T f x x p v h y y y
f x y x y y
(4.1)Also, we define the operator S,Φ by
1
, 0
1/ 2 2
, *
d
, * d ,
n S
S f x x y
r
f x ry x r y
r
(4.2)and the lower dimensional maximal function MΦ by
1 *
1
0 / 2 1 *
,
supr rr , d .
M f x x
r f x t x t
t (4.3)In [10], Fan and Zheng extended the result of Theorem B to the operator TΦ,hfor h∆γ(R+) for γ > 1. Here, we
will obtain the following results.
Theorem 3. Suppose that hL2(R+, r−1dr) and L(log+L)1/2(Sn−1). Then
1) T,h
f L R2
n m
C f L R2
n m
.2) T,h
f L Rp
n m
C f L Rp
n m
, 1 p , provided that the maximal operator M defined in (4.3)is bounded on L Rp
m1
for all p1.Theorem 4. Let Φ and be as in Theorem 3. Then
1) S ,
f L R2
n m
C f L R2
n m
.2) S ,
f L Rp
n m
C f L Rp
n m
, 2 p ,provided that the maximal operator M defined in (4.3)
is bounded on L Rp
m1
for all p1.Clearly, if m = 1 then Theorem 3 and 4 are reduced to Theorem 1 and 2. For m 2, by the same arguments as in the proof of Lemma 2.1, we can obtain the following lemma.
Lemma 4.1. Let L1(Sn−1) and satisfy (1.1). If the maximal operator MΦ in (4.3) is bounded on Lp(Rm+1) for
p > 1, then the following maximal operator M,Φ defined
by
, *
0 *
/ 2 | |
( )( , )
: supr n ,
r y r
M f x x y
f x y x y dy y
(4.4)
2 p is bounded on for . Theorem 1 is proved.
1
p n L R
2
1 p is bounded on L Rp
n m
with bound
1 n1L S
[8] D. Fan and Y. Pan, “Singular Integral Operators with Rough Kernels Supported by Subvarieties,” American
Journal of Mathematics, Vol. 119, No. 4, 1997, pp. 799-
839. doi:10.1353/ajm.1997.0024
1 p .
Then Theorem 3 and 4 follow from this lemma with the arguments and the estimates similar to those in the proofs of our theorems in Section 2. The details are
omitted. [9] D. Fan and Q. Zheng, “Maximal Singular Integral Op-erators along Surfaces,” Journal of Mathematical
Analy-sis and Applications, Vol. 267, No. 2, 2002, pp. 746-759.
doi:10.1006/jmaa.2001.7812
4. Acknowledgements
[10] W. Kim, S. Wainger, J. Wright and S. Ziesler, “Singular Integrals and Maximal Functions Associated to Surfaces of Revolution,” Bulletin London Mathematical Society, Vol. 28, No. 3, 1996, pp. 291-296.
doi:10.1112/blms/28.3.291
The authors are grateful to the referee for his/her helpful comments and suggestions.
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