Hindawi Publishing Corporation Abstract and Applied Analysis Volume 2012, Article ID 583156, 23 pages doi:10.1155/2012/583156 Research Article Carleson Measure and Tent Spaces on the Siegel Upper Half Space Kai Zhao College of Mathematics, Qingdao University, Qingdao 266071, China Correspondence should be addressed to Kai Zhao, zkzc@yahoo.com.cn Received 22 April 2012; Accepted 31 October 2012 Academic Editor: Natig Atakishiyev Copyright q 2012 Kai Zhao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Hausdorff capacity on the Heisenberg group is introduced. The Choquet integrals with respect to the Hausdorff capacity on the Heisenberg group are defined. Then the fractional Carleson measures on the Siegel upper half space are discussed. Some characterized results and the dual of the fractional Carleson measures on the Siegel upper half space are studied. Therefore, the tent spaces on the Siegel upper half space in terms of the Choquet integrals are introduced and investigated. The atomic decomposition and the dual spaces of the tent spaces are obtained at the last. 1. Introduction It is well known that harmonic analysis plays an important role in partial differential equations. The theory of function spaces constitutes an important part of harmonic analysis. Heisenberg group, just as its name coming from the physicists Heisenberg, is very useful in quantum mechanics. Therefore, to discuss new function or distribution spaces and some characterizations of them is very significant in modern harmonic analysis and partial differential equations. Especially, the function spaces related to the Heisenberg group will be used in partial differential equations and physics. It is precisely the reason in which we are interested. The Hausdorff capacity on Rn is introduced by Adams in 1. Some limiting form is the classical Hausdorff measure. Adams also discussed some boundedness of Hardy-Littlewood maximal functions related to it. The capacity and Choquet integrals, in some sense, are from and applied to partial differential equations see 2, 3. As we know, the tent spaces have been considered by many authors and play an important role in harmonic analysis on Rn cf. 4, 5. By using the Choquet integrals with respect to Hausdorff capacity on Rn , the new tent spaces and their applications on the duality results for fractional Carleson measures, 2 Abstract and Applied Analysis Q spaces, and Hardy-Hausdorff spaces were discussed see 6. The theory of Q spaces can be found in 7–11. Inspired by the literature 6, in this paper, we will discuss the fractional Carleson measures and the tent spaces on the Siegel upper half space. In order to get the results in Section 3, some boundedness of Hardy-Littlewood maximal functions q on the Choquet integral space LΛ∞p Hn with Hausdorff capacity on the Heisenberg group are discussed in Section 2. In Section 3, by the Choquet integrals with respect to Hausdorff capacity on the Heisenberg group, we will introduce the fractional Carleson measures on the Siegel upper half space. The characterizations of the fractional Carleson measures on the Siegel upper half space are obtained. And the dual of the fractional Carleson measures on the Siegel upper half space is also obtained. In the last section, the tent spaces on the Siegel upper half space in terms of Choquet integrals with respect to the Hausdorff capacity on the Heisenberg group are introduced. Then, the atomic decomposition and the dual spaces of the tent spaces are obtained. The fractional Carleson measures and the tent spaces on the Siegel upper half space will be used for Q spaces and the Hardy-Hausdorff spaces on the Heisenberg group which will be discussed in another paper by us. On the other hand, they may be used in partial differential equations and quantum mechanics. As we know, Heisenberg group was discussed by many authors, such as 5, 12–15. For convenience, let us recall some basic knowledge for the Heisenberg group. Let Z, R, and C be the sets of all integers, real numbers, and complex numbers, and n n Z , R , and Cn be n-dimensional Z, R, and C, respectively. The Siegel upper half space Un in Cn1 is defined by 2 Un z z , zn1 ∈ Cn1 : Im zn1 > z , where z z1 , z2 , . . . , zn ∈ Cn , |z |2 n k1 1.1 |zk |2 . The boundary of Un is 2 ∂Un z z , zn1 ∈ Cn1 : Im zn1 z . 1.2 The Heisenberg group on Cn × R, denoted by Hn , is a noncommutative nilpotent Lie group with the underlying manifold Cn × R. The group law is given by zw z , t w , s z w , t s 2 Im z w , for z z , t , w w , s ∈ Hn , 1.3 where z w z1 w1 · · · zn wn is the Hermitean product on Cn . It is easy to check that the inverse of the element z z , t is z−1 −z , −t, and the unitary element is 0 0, 0. The Haar measure dz on Hn coincides with the Lebesgue measure dz dt on Cn × R. For each element ζ ζ , t of Hn , the following affine self-mapping of Un : 2 ζ , t : z , zn1 −→ z ζ , zn1 t 2iz ζ iζ 1.4 is an action of the group Hn on the space Un . Observe that the mapping 1.4 gives us a realization of Hn as a group of affine holomorphic bijections of Un see 5. Abstract and Applied Analysis 3 The dilations on Hn are defined by δz δz , t δz , δ2 t, δ > 0, and the rotation on H is defined by σz σz , t σz , t with a unitary map σ of Cn . The conjugation of z is z z , t z , −t. The norm function is given by n 1/4 4 , |z| z |t|2 z z , t ∈ Hn , 1.5 which is homogeneous of degree 1 and satisfies |z−1 | |z| and |zw| ≤ C|z| |w| for some absolute constant C. The distance function dz, w of point z and w in Hn is defined by dz, w |w−1 z|. For z z , t ∈ Hn or z x, y, t ∈ Hn for x x1 , x2 , , . . . , xn , y y1 , y2 , , . . . , yn , we define |z|∞ max |x1 |, . . . , |xn |, y1 , . . . , yn , |t| , 1.6 where z z1 , . . . , zn , and zk xk iyk , 1 ≤ k ≤ n. To define the cube in Hn , let x x1 , x2 , . . . , xn , where a denotes the largest integer less than or equal to a, and x x − x. We define the function Fx, y by ∞ 2 j j n j j n − 2 , 2 x 2 y mod y 2 x mod F x, y 2Z 2Z j j1 4 1.7 and set I0 x, y, t ∈ Hn : 0 ≤ xk ≤ 1, 0 ≤ yk ≤ 1, 1 ≤ k ≤ n, 0 ≤ t − F x, y ≤ 1 , 1.8 Γ {m, n, l ∈ Hn : m, n ∈ Zn ; l ∈ Z}. Then Hn γ −1 I0 , disjoint union , γ∈Γ 1.9 where I0 {x, y, t ∈ Hn : 0 ≤ xk < 1, 0 ≤ yk < 1, k 1, 2, . . . , n, 0 ≤ t − Fx, y < 1} see 14. Now a “cube” in fact, called “tile” more precisely with center w u, v, s and edge sidelength l is defined by I lw−1 I0 . Let |I| with the Lebesgue measure be the volume of I with length lI. It is easy to see that |I| lI2n2 . Obviously, the diameter of I denoted by diamI is equal to cn lI, where cn is a constant depending only on n. The “dyadic cubes” on Hn can be defined by I 2−j γ −1 I0 , γ ∈ Γ, j ∈ Z. We also call the “cube” and “dyadic cube” as cube and dyadic cube, respectively. A ball in Hn with center w and radius r is denoted as B Bw, r {z : |w−1 z| < r}. The tent based on the set E ⊂ Hn is defined by T E ξ, ρ ∈ Un : B ξ, ρ ⊂ E . 1.10 The Schwartz class of rapidly decreasing smooth function on Hn will be denoted by SH . The dual of SHn is S Hn , the space of tempered distributions on Hn . n 4 Abstract and Applied Analysis 2. Hausdorff Capacity on Heisenberg Group In order to discuss the fractional Carleson measures on the Siegel upper half space, we introduce the p-dimensional Hausdorff capacity and Choquet integral on the Heisenberg group in the following. Definition 2.1. For p ∈ 0, 1 and E ⊂ Hn , the p-dimensional Hausdorff capacity of E is defined by ⎫ ⎧ ∞ ⎬ ⎨ I p : E ⊂ Ij , Λ∞ p E inf ⎭ ⎩ j j j1 2.1 where the infimum ranges only over covers of E by dyadic cubes. Remark 2.2. It is easy to check that Λ∞ p satisfies the following properties. ∞ i If Ej is nondecreasing, then Λ∞ p j Ej limj → ∞ Λp Ej . ∞ ii If Ej is nonincreasing, then Λ∞ p j Ej limj → ∞ Λp Ej . iii Λ∞ p has the strong subadditivity condition. ∞ ∞ E2 Λ∞ Λ∞ p E1 p E1 ∩ E2 ≤ Λp E1 Λp E2 . 2.2 For a nonnegative function f on Hn , the Choquet integral with respect to the Hausdorff capacity on the Heisenberg group is defined by Hn fzdΛ∞ p ∞ 0 Λ∞ p z ∈ Hn : fz > λ dλ. 2.3 Since Λ∞ p is monotonous, the integrand on the right hand side in 2.3 is nonincreasing and then is Lebesgue measurable on 0, ∞. It is easy to see that the equality 2.3 with the Hausdorff measure is similar to the equality of the distribution function with Lebesgue measure. In order to characterize the fractional Carleson measure in the Siegel upper half space in Section 3, we need to discuss the Hardy-Littlewood maximal operator on the Heisenberg group. Let f ∈ L1loc Hn . Mf, the dyadic Hardy-Littlewood maximal operator of f, is defined by 1 M f z sup Iz |I| I fξdξ, 2.4 where the supremum is taken over all dyadic cubes I containing z. The boundedness of the dyadic Hardy-Littlewood maximal operators on the Choquet q integral spaces LΛ∞p Hn is as follows. Abstract and Applied Analysis 5 Theorem 2.3. Suppose 0 < p ≤ 1. There exists a constant C depending only on p and n such that Hn Λ∞ p q M f dΛ∞ p ≤C Hn q ∞ f dΛp , C ξ ∈ Hn : M f ξ > λ ≤ p λ Hn q ∀f ∈ LΛ∞p Hn , q > p, p ∞ f dΛp , p ∀f ∈ LΛ∞p Hn . 2.5 2.6 To prove Theorem 2.3, we need to prove the following lemmas first. Lemma 2.4. For p ∈ 0, 1, let {Ij } be a sequence of dyadic cubes in Hn such that j |Ij |p < ∞. Then there is a sequence of disjoint dyadic cubes {Jk } so that k Jk j Ij and k |Jk |p ≤ j |Ij |p . Moreover, if E ⊂ j Ij , then the following tent inclusion T E ⊂ k T Jk∗ holds, where Jk∗ is the cube with the same center as Jk and δn times the sidelength (δn is some constant depending only on n). Proof. Since j |Ij |p < ∞, p ∈ 0, 1, we have that j |Ij | < ∞. Thus the union of Ij cannot form arbitrarily large dyadic cubes. Thus, each Ij must be included in some maximal dyadic cube Jk ∈ J, where J denotes the collection of all dyadic cubes J {Ij : Ij ⊂ J}. If we write these maximal cubes as a sequence {Jk }, then Jk is disjoint and k Jk j Ij . By the definition of Jk in J, we know that |Jk | ≤ Ij ⊂Jk |Ij |. Jensen’s inequality gives |Jk |p ≤ Ij ⊂Jk |Ij |p for 0 < p ≤ 1. Consequently, k |Jk |p ≤ p p Ij ≤ Ij . k Ij ⊂Jk 2.7 j Suppose that E ⊂ j Ij and ξ, ρ ∈ T E. Then ξ ∈ E ⊂ k Jk and ξ ∈ Jk for some fixed k. For this Jk , we consider the parent dyadic cube Jk , namely, the unique dyadic cube containing Jk whose sidelength is double of that of Jk . Since Jk is maximal in J, we have that Jk is not a union of the Ij ’s, that is, Jk contains a point η ∈ Hn \ j Ij ⊂ Hn \ E. Denoting the boundary of E by ∂E, there is ρ < distξ, ∂E ≤ diam Jk cn l Jk 2cn lJk . 2.8 If Jk∗ is the cube with the same center as Jk , and 5cn times the sidelength, then 1 dist ξ, ∂Jk∗ ≥ 5cn − 1lJk ≥ 2cn lJk > ρ, 2 since cn > 1, 2.9 which means that ξ, ρ ∈ T Jk∗ . The proof is completed. Lemma 2.5. Let χI be the characteristic function on the cube I. Then Hn q p M χI dΛ∞ p ≤ C|I| , q > p. 2.10 6 Abstract and Applied Analysis Proof. Let zI be the center of I. By the definition of the maximal function M, we obtain ⎫ ⎧ ⎬ ⎨ |I| . M χI ξ ≤ C inf 1, ⎩ z−1 ξ2n2 ⎭ 2.11 I Since p/q < 1, there is Hn q p M χI dΛ∞ p ≤ C|I| C 1 |I|p λ−p/q dλ C|I|p . 2.12 0 The proof of Lemma 2.5 is complete. Lemma 2.6. Let {Ij } be a family of nonoverlapping dyadic cubes. Then there is a maximal subfamily {Ijk } such that for every dyadic cube I, p Ij ≤ 2|I|p , k Ijk ⊂I Λ∞ p p Ij ≤ 2 Ijk . k 2.13 2.14 Proof. Similar to the proof in 16, if Ij1 I1 , then obviously Ij1 satisfies 2.13. If j1 , . . . , jk have been chosen so that 2.13 holds, then we define jk1 as the first index such that the family {Ij1 , . . . , Ijk , Ijk1 } satisfies 2.13. Continuing this proceeding, therefore, we have that {Ijk } is a maximal subfamily of {Ij } satisfying 2.13. Hence 2.13 holds. To prove 2.14, let j be an index such that jm < j < jm1 for some m ∈ Z. Then by the proof of 2.13, there exists a dyadic cube Ij∗ ⊃ Ij such that p p p Ij Ij > 2I ∗ . k j Ijk ⊂Ij∗ ,k≤m 2.15 Therefore, p ∗ Ij ≤ Ijk ⊂Ij∗ ,k≤m p Ij . k 2.16 We can assume that k |Ijk |p < ∞. Otherwise 2.14 is obviously correct. Then the sequence {|Ij∗ |} is bounded. Thus, we can consider the family {Il } of maximal cubes of the family {Ij∗ }. Hence Ij ⊂ j Ijk k Il . l 2.17 Abstract and Applied Analysis 7 Consequently, by the definition of Λ∞ p , we obtain Λ∞ p p Ij ≤ 2 Ijk . 2.18 k The proof is complete. Proof of Theorem 2.3. By the definition of Λ∞ p , for any ε > 0, there exist {Ij }j such that p Ij < Λ∞ p Ek ε, 2.19 j where Ek {ξ ∈ Hn : 2k < |fξ| ≤ 2k1 }. If Λ∞ p Ek 0, we can choose Λ∞ p Ek > 0, then p Ij ≤ 2Λ∞ p Ek . j |Ij |p 0. If 2.20 j k By Lemma 2.4, for each integer k, there is a family of nonoverlapping dyadic cubes {Ij } such that k ξ ∈ Hn : 2k < fξ ≤ 2k1 ⊂ Ij , j k p ξ ∈ Hn : 2k < fξ ≤ 2k1 . Ij ≤ 2Λ∞ p 2.21 j k Set g k 2k1q χFk , where χFk is the characteristic function of Fk j Ij . Then |f|q ≤ g. First, assume that q > 1. Then the Hölder inequality tells us ! " q q k1q 2 M χI k . M f ≤M f ≤M g ≤ k j j 2.22 Therefore, by Lemma 2.5, we have Hn q M f dΛ∞ 2k1q p ≤ C j k ≤C k 2k1q Hn ! " M χI k dΛ∞ p j k p Ij ≤ C 2k1q Λ∞ p Ek j k 2kq 22q q ≤C Λ∞ ξ ∈ Hn : fξ > λ dλ p q −1 2 2k−1q k ∞ q q ∞ ∞ n f dΛp . Λp ξ ∈ H : fξ > λ dλ C ≤C 0 Hn 2.23 8 Abstract and Applied Analysis Now, assume that p < q ≤ 1. Since |f| ≤ k 2k1 χFk , there is " ! k1 M f ≤ 2 M χI k . 2.24 j j k By using Jensen’s inequality, we obtain ! "q q k1q k M f ≤ 2 M χI . 2.25 j j k Thus, also by Lemma 2.5, there is Hn q M f dΛ∞ 2k1q p ≤ C j k ≤C 2k1q ∞ 0 Hn ! " M χI k dΛ∞ p j k p Ij ≤ C 2k1q Λ∞ p Ek j k ≤C Λ∞ p 2.26 k q ξ ∈ Hn : fξ > λ dλ C Hn q ∞ f dΛp . That means that 2.5 holds. For a given λ > 0, let {Ij } be the family of maximal dyadic cubes Ij such that 1 Ij fξdξ > λ. Note that Mf is dyadic and {z ∈ Hn : Mfz > λ} ⎛ ⎞1/p p Ij ≤ ⎝ Ij ⎠ , j j 2.27 Ij j Ij . Since 0 < p ≤ 1, there is 1/p ∞ Λ∞ . 1 E ≤ Λp E 2.28 Abstract and Applied Analysis 9 Hence Hn fzdz ∞ 0 ≤ 1 p 1 p Λ∞ 1 ∞ 0 ∞ 0 ξ ∈ Hn : fξ > λ dλ Λ∞ 1 ξ ∈ Hn : fξ > ρ1/p ρ1/p−1 dρ Λ∞ p 1/p ξ ∈ Hn : fξ > ρ1/p ρ1/p−1 dρ p 1/p−1 ∞ 1 ∞ ∞ Λp ξ ∈ Hn : fξ|p > ρ ρ Λp ξ ∈ Hn : fξ > ρ dρ p 0 ! "1/p−1 ∞ p p 1 f dΛ∞ ≤ Λ∞ ξ ∈ Hn : fξ > ρ dρ p p p Hn 0 ! "1/p p 1 f dΛ∞ , p p Hn 2.29 where the last inequality is due to the fact that Λ∞ p p ξ ∈ Hn : fξ > ρ ρ ≤ {ξ∈Hn :|fξ|p >ρ} p ∞ f dΛp , ρ > 0. 2.30 Therefore, by 2.27 and 2.29, we obtain p Ij ≤ 1 f dξ λ Ij p ≤ Cλ −p Ij p ∞ f dΛp . 2.31 For the above {Ij }, by Lemma 2.6 and 2.31, there exists a subfamily {Ijk } such that ⎛ ⎞ ⎝ Ij ⎠ ≤ 2 Ijk p Λ∞ z ∈ Hn : M f z > λ Λ∞ p p j ≤ Cλ−p k k Ij k p ∞ f dΛp ≤ Cλ−p Hn p ∞ f dΛp . 2.32 The proof of Theorem 2.3 is complete. 3. p-Carleson Measure on Siegel Upper Half Space Let I be a cube in Hn with center η. The Carleson box based on I is defined by SI lI −1 ξ, ρ ∈ U : η ξ ≤ , ρ ≤ lI . ∞ 2 n 3.1 10 Abstract and Applied Analysis For p > 0, a positive Borel measure μ on the Siegel upper half space Un is called a p-Carleson measure if there exists a constant C > 0 such that μSI ≤ C|I|p , ∀ cubes I ⊂ Hn . 3.2 For z ∈ Hn , let Γz {ξ, ρ ∈ Un : |z−1 ξ| < ρ} be the cone at z. Suppose that f is a measurable function on Un . The nontangential maximal function Nf of f is defined by N f z sup f ξ, ρ . 3.3 ξ,ρ∈Γz Since the nontangential maximal function and Hausdorff capacity are defined, we are paying attention on the characterizations of the p-Carleson measures. Theorem 3.1. For p ∈ 0, 1, let μ be a positive Borel measure on Un . Then the following three conclusions are equivalent. i μ is a p-Carleson measure. ii There exists a constant C > 0 such that Un f ξ, ρ dμ ≤ C Hn ∞ N f dΛp 3.4 holds for all Borel measurable functions f on Un . iii For every q > 0, there exists a constant C > 0 such that Un q f ξ, ρ dμ ≤ C Hn q ∞ N f dΛp 3.5 holds for all Borel measurable functions f on Un . Proof. i⇒ii. Assume that μ is a p-Carleson measure, and f is a Borel measurable function on Un . For λ > 0, let Eλ {z ∈ Hn : Nfz > λ}. If the integral on the right hand side of 3.4 ∞ is finite, we may assume that Λp Eλ < ∞. Let {Ij } be any of the dyadic cubes covering of Eλ with j |Ij |p < ∞. Then Lemma 2.4 tells us that there is a sequence {Jk } of dyadic cubes with mutually disjointed so that k Jk j Ij , k |Jk |p ≤ j |Ij |p and T Eλ ⊂ k T Jk∗ , where Jk∗ is the cube with the same center and 5cn times sidelength of Jk . If ξ, ρ ∈ Un satisfies |fξ, ρ| > λ, then Nfz > λ for all z ∈ Bξ, ρ. Thus ξ, ρ ∈ T Eλ , and hence ξ, ρ ∈ Un : f ξ, ρ > λ ⊂ T Eλ ⊂ T Jk∗ . k 3.6 Abstract and Applied Analysis 11 By Lemma 2.4, we obtain μ T Jk∗ ξ, ρ ∈ U : f ξ, ρ > λ ≤ μ ≤ n k ' ' p ≤ C'μ' Jj∗ . ' ' p μ T Jk∗ ≤ C'μ' Jk∗ k k 3.7 j Taking an infimum over all such dyadic cube coverings, we have μ ' ' ∞ ξ, ρ ∈ Un : f ξ, ρ > λ ≤ C'μ'Λp Eλ . 3.8 Therefore, Un f ξ, ρ dμ ∞ μ ξ, ρ ∈ Un : f ξ, ρ > λ dλ 0 ≤C ∞ ' ' ' ' ∞ 'μ'Λp Eλ dλ C'μ' 0 Hn ∞ N f dΛp . 3.9 ii⇒i. Suppose that 3.4 is valid for all Borel measurable functions on Un . For a cube I ⊂ H , let φξ, ρ χT I . Note that ξ, ρ ∈ T I ∩ Γz if and only if z ∈ Bξ, ρ ⊂ I, there is Nφ χI . Then, by 3.4, we have n μT I ≤ C ∞ ∞ Λp N φ > λ dλ C 0 1 ∞ Λp Idλ ≤ C|I|p . 3.10 0 It means that μ is a p-Carleson measure. ii⇒iii. Replacing |f| with |f|q in 3.4 for q > 0, we immediately obtain Un q f ξ, ρ dμ ≤ C Hn q ∞ N f dΛp . 3.11 iii⇒ii. If we set q 1 in 3.5, then 3.4 holds. The proof of Theorem 3.1 is complete. To continue the characterization of the p-Carleson measures on the Siegel upper half space, we need to prove the following Lemma 3.2. It is said that the nontangential maximal functions are dominated by the dyadic Hardy-Littlewood maximal operators on the Heisenberg group. 12 Abstract and Applied Analysis Lemma 3.2. Let f be a locally integrable function on Hn , and φ ∈ SHn be a nonnegative radial and ( decreasing function with Hn φz dz 1. Then NFz sup F ξ, ρ ξ,ρ∈Γz sup f ∗ φρ ξ ≤ CM f z, ξ,ρ∈Γz 3.12 where φρ ξ ρ−2n2 φρ−1 ξ and ρ > 0 is real. Proof. Since φ ∈ SHn , we can suppose that |φz| ≤ C/1 |z|2n2ε for some ε > 0. Then f ∗ φρ ξ ≤ Hn ρ−2n2 φ ρ−1 η−1 ξ f η dη |η−1 ξ|≤ρ ∞ 2k ρ<|η−1 ξ|≤2k1 ρ k0 ≤ ρ−2n2 φ ρ−1 η−1 ξ f η dη C ρ2n2 |η−1 ξ|≤ρ ρ−2n2 φ ρ−1 η−1 ξ f η dη ∞ f η dη C k0 ∞ 1 ≤ CM f ξ C 2n2 ρ k0 2k ρ<|η−1 ξ|≤2k1 ρ |η−1 ξ|≤2k1 ρ 1 2k2n2ε ρ−2n2 f η 2n2ε dη 1 η−1 ξ /ρ 3.13 f η dη ∞ ≤ C M f ξ 2−k1ε C M f ξ. k0 Hence NFz sup f ∗ φρ ξ ≤ CM f z. ξ,ρ∈Γz 3.14 Lemma 3.2 is proved. Theorem 3.3. For 0 < p ≤ 1, q > p, let μ be a positive Borel measure on Un . Then μ is a p-Carleson measure if and only if Un q G ξ, ρ dμ ≤ C Hn q ∞ g dΛp 3.15 holds for all functions G on Un which can be written as Gξ, ρ g ∗ φρ ξ, where g is a locally integrable function on Hn , and φ is the function in Lemma 3.2. Abstract and Applied Analysis 13 Proof. Suppose that μ is a p-Carleson measure. By the conclusions of Theorems 3.1 and 2.3 and Lemma 3.2, there is Un q G ξ, ρ dμ ≤ C ∞ Hn NGq dΛp ≤C q ∞ M g dΛp ≤ C Hn Hn q ∞ g dΛp . 3.16 Conversely, for any cube I ⊂ Hn , if we set g χI , then for ξ, ρ ∈ T I, there is G ξ, ρ −1 φρ η ξ dη ≥ −1 φρ η ξ dη I Bξ,ρ φ1 η−1 ξ dη Bξ,1 3.17 φzdz c. B0,1 Thus, by using the inequality 3.15, we obtain cq μT I cq C T I Hn dμ ≤ ∞ χI dΛp T I q G ξ, ρ dμ ≤ ∞ CΛp I Un q G ξ, ρ dμ ≤ C Hn q ∞ g dΛp 3.18 p ≤ C|I| . This ends the proof of Theorem 3.3. ∞ Let NΛp be the space of all Borel measurable functions f on Un satisfying ' ' 'f ' ∞ NΛp Hn ∞ N f dΛp < ∞. 3.19 ∞ gives a quasi norm and NΛp is complete. Then · NΛ∞ p ∞ The following result says that NΛp is the dual of p-Carleson measure. Theorem 3.4. Let p ∈ 0, 1. Then there exists a duality between the space of p-Carleson measures ∞ and NΛp in the following sense. ∞ i Every p-Carleson measure μ on Un defines a bounded linear functional on NΛp via the pairing ) ∞ * μ, f Un f ξ, ρ dμ. 3.20 ∞ ii Let N0 Λp be the closure in NΛp of the continuous functions with compact support ∞ in Un . Then every bounded linear functional on N0 Λp given via the pairing 3.20 by a Borel measure μ on Un is a p-Carleson measure. 14 Abstract and Applied Analysis ∞ Proof. Assume that μ is a p-Carleson measure and f ∈ NΛp . By 3.19 and ii in Theorem 3.1, we have Un f ξ, ρ dμ ≤ C Hn ∞ N f dΛp < ∞. 3.21 ( Thus, μ, f Un fξ, ρdμ is well defined. Hence, every p-Carleson measure μ defines a ∞ bounded linear functional on NΛp . The part i is proved. ∞ For part ii, let L be a bounded linear functional on N0 Λp . By the continuity and ∞ the closure of N0 Λp , applying the Riesz representation theorem, we obtain a Borel measure μ on Un having L f Un ) * f ξ, ρ dμ μ, f . 3.22 If f χT I for any cube I ∈ Hn , then μT I Un L ' ' χT I dμ L χT I ≤ L · 'χT I 'NΛ∞ p Hn ∞ N χT I dΛp CL 3.23 ∞ dΛp ∞ CLΛp I p ≤ CL · |I| . I Hence, μ is a p-Carleson measure with μ ≤ CL. This ends the proof of Theorem 3.4. 4. Tent Spaces with Hausdorff Capacity With Hausdorff capacity on the Heisenberg group discussed above, in this section, we introduce the tent spaces on the Siegel upper half space, an analogy of the Coifman-MeyerStein tent space on Rn cf. 4, 6. Then the atomic decomposition of the tent spaces and the duality of the tent space are discussed. Definition 4.1. Let p ∈ 0, 1. A Lebesgue measurable function f on Un is said to belong to Tp∞ if ' ' 'f ' ∞ sup Tp B⊂Hn 1 |B|p T B 2 f ξ, ρ dξdρ 1/2 < ∞, ρ12n11−p 4.1 where B runs over all balls in Hn , and T B is a tent based on B. Definition 4.2. Let p ∈ 0, 1. The tent space Tp1 consists of all measurable functions f on Un for which ' ' 'f ' 1 inf Tp w Un 2 −1 f ξ, ρ w ξ, ρ dξdρ ρ1−2n11−p 1/2 < ∞, 4.2 Abstract and Applied Analysis 15 where the infimum is taken over all nonnegative Borel measurable functions w on Un satisfying ∞ Hn NwdΛp ≤ 1, 4.3 and w is allowed to vanish only where f vanishes. We will identify Tp∞ with a dual space of Tp1 . In order to do this, we first introduce the 1 Tp -atom as follows. Definition 4.3. A function a on Un is said to be a Tp1 -atom, if there exists a ball B ⊂ Hn such that a is supported in the tent T B and satisfies T B 2 a ξ, ρ dξdρ ρ1−2n11−p ≤ 1 . |B|p 4.4 For the tent space Tp1 on Un and · Tp1 , we have the triangle inequality with a constant in the following lemma. Lemma 4.4. Let p ∈ 0, 1. If j gj Tp1 < ∞, then g j gj ∈ Tp1 and ' ' ' ' 'g ' 1 ≤ C 'gj ' 1 . Tp T 4.5 p j Proof. Without loss of generality, we assume that λj gj Tp1 > 0 for all j. Set fj g−1 g. Tp1 j ( ∞ Then fj Tp1 ≤ 1 and g j λj fj . Suppose that wj ≥ 0 for all j such that Hn Nwj dΛp ≤ 1 and Un 2 −1 gj ξ, ρ wj ξ, ρ dξdρ ρ1−2n11−p ' '2 ≤ 2'gj 'T 1 . p 4.6 According to the definition of Tp1 , the above inequality holds obviously. By using the CauchySchwarz inequality, we have ⎛ ⎞⎛ ⎞ 2 2 g ≤ ⎝ λj wj ⎠⎝ λj fj w−1 ⎠. j j 4.7 j Let w j λj −1 j λj wj . Notice that the vanishing of w implies the vanishing of all wj , which can only happen whenever all the gj vanish, that is, g 0, then ∞ Hn NwdΛp ⎛ ⎞−1 ≤ ⎝ λj ⎠ λj j j Hn ∞ N wj dΛp ≤ 1. 4.8 16 Abstract and Applied Analysis Thus, by the inequality 4.7, we obtain Un 2 −1 g ξ, ρ w ξ, ρ dξdρ ρ1−2n11−p ⎛ ⎞ ≤ C⎝ λj ⎠ λj j ⎛ ≤ 2C⎝ j j Hn 2 −1 fj ξ, ρ wj ξ, ρ dξdρ 4.9 ρ1−2n11−p ⎞ ⎞2 ⎞2 ⎛ ⎛ ' '2 ' ' λj ⎠ λj 'fj 'T 1 C⎝ λj ⎠ C⎝ 'gj 'T 1 ⎠ . p j j j p Taking the infimum on the left above inequality, we have ' ' ' ' 'g ' 1 ≤ C 'gj ' 1 . Tp T j 4.10 p The proof of Lemma 4.4 is complete. Remark 4.5. By Lemma 4.4, one can show that · Tp1 is a quasinorm and the tent space Tp1 is complete. The main result of this section is the atomic decomposition of the tent space Tp1 as follows. Theorem 4.6. Let p ∈ 0, 1. Then a function f on Un belongs to Tp1 if and only if there exist a sequence of Tp1 -atoms {aj } and an l1 -sequence {λj } such that f λj aj . 4.11 j Moreover, ' ' 'f ' Tp1 ⎧ ⎫ ⎨ ⎬ λj : f ≈ inf λj aj , ⎩ j ⎭ j 4.12 where the infimum is taken over all possible atomic decompositions of f ∈ Tp1 . Note that the right hand side of 4.12 in fact defines a norm and then Tp1 becomes a Banach space. Proof. Suppose that a is a Tp1 -atom on Un . Then there exists a ball B Bz, r ⊂ Hn such that supp a ⊂ T B and T B 2 a ξ, ρ dξdρ ρ1−2n11−p ≤ 1 . |B|p 4.13 Abstract and Applied Analysis 17 Fix ε > 0, and let + ! −2n2p w ξ, ρ hr min 1, r Dξ, z "2n2pε , , 4.14 where Dξ, z denotes the distance between ξ, ρ and z, 0 in Un , and h is a suitable constant which will be chosen later. Obviously, wξ, ρ is identically equal to hr −2n2p on the upper half ball of radius r center is z, 0, and Dξ, z ≤ r and decays radially outside the ball outside the ball Dξ, z > r, and Dξ, z → ∞. For ξ ∈ Hn , the distance in Un from the cone Γξ to z, 0 is c|z−1 ξ| cdz, ξ. Then Nwz ≤ hr −2n2p + ! min 1, r cdξ, z "2n2pε , . 4.15 Therefore, −1 h Hn ∞ NwdΛp ∞ ∞ Λp ξ ∈ Hn : h−1 Nw > λ dλ 0 ≤ r −2n2p - ∞ Λp 0 ≤C r −2n2p . ! " 1 r ε 1/2n2pε dλ B z, c λ - ∞ Λ p 0 . ! " 1 r ε 1/2n2pε dλ B z, c λ 4.16 2n2p r −2n2p ≤ C r ε/2n2pε λ−2n2p/2n2pε dλ C. 0 ( ∞ Thus, Hn Nw dΛp ≤ 1 by choosing h C−1 . On the other hand, let w−1 r 2n2p on T B. We have T B 2 −1 a ξ, ρ w ξ, ρ dξdρ ρ1−2n11−p r 2n2p ≤r 2n2p T B −p |B| 2 a ξ, ρ dξdρ ρ1−2n11−p 4.17 C. Therefore, a ∈ Tp1 and aTp1 ≤ C. Now, taking a sum j λj aj , where j |λj | < ∞ and every aj is Tp1 -atom on Un , by Lemma 4.4, the sum converges in the quasinorm to f ∈ Tp1 with ' ' ' ' 'f ' 1 ≤ λj 'aj ' 1 ≤ C λj < ∞. Tp T j That means f j λj aj ∈ Tp1 . p j 4.18 18 Abstract and Applied Analysis Conversely, let f ∈ Tp1 . We choose a Borel measurable function w ≥ 0 on Un such that 4.3 holds and Un ∞ Λp , 2 −1 f ξ, ρ w ξ, ρ dξdρ ρ1−2n11−p ' '2 ≤ 2'f 'Tp1 . 4.19 For each k ∈ Z, let Ek {Z ∈ Hn : Nwz > 2k }. By Lemma 2.4 and the definition of it follows that there exists a disjoint dyadic cubes sequence {Ik,j } such that p Ik,j ≤ 2Λ∞ p Ek , T Ek ⊂ j S∗ Ik,j , j 4.20 where S∗ Ik,j {ξ, ρ ∈ Un : ξ ∈ Ik,j , ρ < 2 diamIk,j }. Define ∗ Tk,j S∗ Ik,j \ S Im,l . 4.21 m>k l Then Tk,j is disjoint in Un for different j, k. Therefore, K ∗ Tk,j S∗ I−K,j \ S Im,l ⊃ T E−K \ S∗ Im,l . k−K j j m>k l 4.22 m>k l Note that k T Ek {ξ, ρ ∈ Un : wξ, ρ > 0}, ξ, ρ ∈ / T Ek implies wξ, ρ ≤ 2k . And each S∗ Im,l is contained in a cube of sidelength 4 diamIm,l in Un . By using the subadditivity of the p-Hausdorff capacity and 4.3, there is ∞ Λp S∗ Im,l m>k l ≤C |Im,l |p ≤ C m>k l ∞ Λp Em −→ 0 4.23 m>k as k → ∞. Thus, by 4.21, k j Tk,j ⊃ k T Ek \ / k m>k l S∗ Im,l ξ, ρ ∈ Un : w ξ, ρ > 0 \ E∞ , 4.24 Abstract and Applied Analysis 19 where E∞ is a set of zero p-Hausdorff capacity, that is, ∞ Λp E∞ / S∗ Im,l ∞ Λp 0. 4.25 k m>k l Since w is allowed to vanish only where f vanishes, we have f p ∗ Ik,j ak,j 2 f ξ, ρ Tk,j λk,j p ∗ Ik,j ρ1−2n11−p Tk,j k,j f · χTk,j a.e. on Un . Let −1/2 dξdρ 2 f ξ, ρ dξdρ f · χTk,j , 4.26 1/2 ρ1−2n11−p , ∗ ∗ where the Ik,j is a cube as Lemma 2.4, that is, Ik,j 5cn Ik,j . Thus f λk,j ak,j , a.e. on Un . 4.27 k,j Note that, by 4.21, Tk,j ⊂ S∗ Ik,j ⊂ T Bk,j , where Bk,j is the ball with the same center as Ik,j ∗ and radius clIk,j c > 1 is a constant. Thus, ak,j is supported in T Bk,j , and T Bk,j 2 ak,j ξ, ρ dξdρ ρ1−2n11−p p ∗ Ik,j 2 f ξ, ρ Tk,j −1 dξdρ ρ1−2n11−p T Bk,j 2 f · χTk,j dξdρ 4.28 ρ1−2n11−p −p −p ∗ Ik,j CBk,j . This means that every ak,j is a Tp1 -atom. The remaining is to estimate Notice the fact that w≤2 k1 on Tk,j ⊂ S∗ Ik1,l l k,j |λk,j |. c ⊂ T Ek1 c . 4.29 20 Abstract and Applied Analysis By the Cauchy-Schwarz inequality, 4.19 and 4.20, we have p/2 k1/2 ∗ λk,j ≤ 2 Ik,j k,j k,j 2 −1 f ξ, ρ w ξ, ρ Tk,j ⎞1/2 ⎛ ⎛ p k1 ∗ ⎠ ⎝ ⎝ ≤ 2 Ik,j k,j k,j 1/2 dξdρ ρ1−2n11−p 2 −1 f ξ, ρ w ξ, ρ Tk,j ⎞1/2 dξdρ ρ1−2n11−p ⎛ ⎞1/2 p ' ' ' ' ∞ k Ik,j ⎠ ≤ C'f ' 1 ≤ C'f 'Tp1 ⎝ 2 2k Λp Ek Tp j k ' ' C'f 'Tp1 ' ' ≤ C'f 'Tp1 If f k ! ∞ ⎠ 1/2 4.30 k "1/2 ∞ Λp {ξ ∈ Hn : Nw > λ}dλ 0 ! ∞ Hn "1/2 NwdΛp ' ' ≤ C'f 'Tp1 . λk ak and every ak is a Tp1 -atom, then, by Lemma 4.4, we obtain ' ' 'f ' 1 ≤ C |λk |ak 1 ≤ C |λk |. T Tp p k k 4.31 Thus ' ' 'f ' Tp1 ⎧ ⎫ ⎨ ⎬ λj : f ≈ inf λj aj , ⎩ j ⎭ j 4.32 where the infimum is taken over all atomic decompositions of f ∈ Tp1 . The proof is complete. The dual result is as follows. Theorem 4.7. Let p ∈ 0, 1. Then the dual of Tp1 can be identified with Tp∞ under the pairing ) * f, g dξdρ . f ξ, ρ g ξ, ρ ρ Un 4.33 Proof. We first show that ' ' ' ' dξdρ f ξ, ρ g ξ, ρ ≤ C'f 'Tp1 'g 'Tp∞ ρ Un holds for all f ∈ Tp1 and g ∈ Tp∞ . 4.34 Abstract and Applied Analysis 21 In fact, assume that w is a nonnegative Borel measurable function on Un satisfying inequality 4.3 in Definition 4.2 and g ∈ Tp∞ . Then there exists a constant C for any ball B ⊂ Hn satisfying 1 |B|p T B 2 g ξ, ρ dξdρ ρ12n11−p ≤ C. 4.35 It means that |gξ, ρ|2 ρ−2n11−p−1 dξdρ is a p-Carleson measure, and μ ≈ g2Tp∞ . Hence, by Theorem 3.1, we obtain Un ' '2 2 w ξ, ρ g ξ, ρ ρ−2n11−p−1 dξdρ ≤ C'g 'Tp∞ ∞ Hn NwdΛp ' '2 ≤ C'g 'Tp∞ . 4.36 Thus, for f ∈ Tp1 , by using the Cauchy-Schwarz inequality, there is dξdρ f ξ, ρ g ξ, ρ ρ Un 2 −1 dξdρ f w ≤ 1−2n11−p ρ Un ≤C Un 2 −1 f ξ, ρ w ξ, ρ 1/2 Un 2 g w dξdρ ρ12n11−p 1/2 dξdρ ρ1−2n11−p 1/2 4.37 ' ' · 'g 'Tp∞ ' ' ' ' ≤ C'f 'Tp1 'g 'Tp∞ . This gives 4.34. Thus, every g ∈ Tp∞ induces a bounded linear functional on Tp1 via the pairing 4.33. It suffices to prove the converse. Let L be a bounded linear functional on Tp1 and fix a ball B Bz, r ⊂ Hn . If f is supported in T B with f ∈ L2 T B, ρ−1 dξdρ, then T B 2 f ξ, ρ dξdρ ρ1−2n11−p ≤ r 2n11−p Cr 2n1 2 dξdρ f ξ, ρ ρ T B ' '2 |B| f 'L2 T B,ρ−1 dξdρ . 4.38 −p ' Therefore, f is a multiple of a Tp1 -atom with ' '2 ' ' 'f ' 1 ≤ Cr 2n1 'f '2 2 . Tp L T B,ρ−1 dξdρ 4.39 22 Abstract and Applied Analysis Hence, L induces a bounded linear functional on L2 T B, ρ−1 dξdρ. Thus, there exists a function g which is locally in L2 Un , ρ−1 dξdρ such that L f dξdρ , f ξ, ρ g ξ, ρ ρ Un 4.40 whenever f ∈ Tp1 with support in some finite tent T B. By the atomic decomposition of tent function in Theorem 4.6, obviously, the subspace of such f is dense in Tp1 . Therefore, the rest of the proof is to show that g ∈ Tp∞ and gTp∞ ≤ CL. Now, again fix a ball B ⊂ Hn and for every ε > 0, let fε ξ, ρ ρ−2n11−p g ξ, ρ χT ε B ξ, ρ , 4.41 where T ε B T B ∩ {ξ, ρ : ρ > ε} is the truncated of T B. Since g ∈ L2 T B, there is T B 2 fε ξ, ρ dξdρ ρ1−2n11−p T ε B 2 g ξ, ρ dξdρ ρ12n11−p < ∞. 4.42 Hence, fε is a multiple of a Tp1 -atom with ' '2 'fε ' 1 ≤ Cr 2n1p Tp T ε B 2 g ξ, ρ dξdρ ρ12n11−p 4.43 , where C is independent of ε. By 4.40, we obtain T ε B 2 g ξ, ρ dξdρ ρ12n11−p ' ' L fε ≤ L · 'fε 'Tp1 ≤ CL |B| p T ε B 2 g ξ, ρ dξdρ ρ12n11−p 4.44 1/2 . Thus −p |B| T ε B 2 g ξ, ρ dξdρ 1/2 ρ12n11−p ≤ CL. 4.45 ≤ CL, 4.46 It follows that −p |B| T B 2 g ξ, ρ dξdρ ρ12n11−p 1/2 Abstract and Applied Analysis 23 since 4.40 is true for all ε > 0. Therefore, g ∈ Tp∞ and gTp∞ ≤ CL. In fact, in 4.40, we can replace the local function g by ordinary. Thus, we obtain the representation of L via the pairing 4.40 for all f ∈ Tp1 . This ends the proof of Theorem 4.7. Acknowledgments The author would like to thank the referees for their meticulous work and helpful suggestions, which improve the presentation of this paper. 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