Sparse Bounds in Harmonic Analysis and Semiperiodic Estimates
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Sparse Bounds in Harmonic Analysis and Semiperiodic Estimates by Alexander Barron May 2019 2 c Copyright 2019 by Alexander Barron i This dissertation by Alex Barron is accepted in its present form by the Department of Mathematics as satisfying the dissertation requirement for the degree of Doctor of Philosophy Date Jill Pipher, Ph.D., Advisor Recommended to the Graduate Council Date Benoit Pausader, Ph.D., Reader Date Sergei Treil, Ph.D., Reader Approved by the Graduate Council Date Andrew G. Campbell, Dean of the Graduate School ii Vitae Alexander Barron graduated from Colby College with a B.A. in Mathematics in May 2013 (summa cum laude, Phi Beta Kappa). He also earned an M.S. in mathematics from Brown University in May 2016. At Brown he was a teaching assistant and instructor for multiple sections of Calculus I and II, and also for multivariable calculus. He has given research talks at various conferences and institutions, including Georgia Tech, the University of Virginia, the University of New Mexico, and the American Institute of Math (AIM). Starting in August 2019 he will be serving as a Doob Visiting Assistant Professor at the University of Illinois Urbana- Champaign. Below is a list of publications and preprints by the author. 1. Weighted Estimates for Rough Bilinear Singular Integrals via Sparse Domination, N.Y. Journal of Math 23 (2017) 779-811. 2. Sparse bounds for bi-parameter operators using square functions, with Jill Pipher. Preprint arXiv:1709.05009. 3. Sparse domination and the strong maximal function, with Jos´eConde Alonso, Yumeng Ou, and Guillermo Rey. Adv. Math. 345 (2019), 1-26. 4. On Global-in-time Strichartz estimates for the semiperiodic Schr¨odingerequation. Preprint, arXiv:1901.01663 iii iv Preface Part I of this thesis studies some results related to sparse bounds in harmonic analysis. We provide a brief overview of sparse bounds in Chapter 1. In Chapter 2 we study sparse bounds for certain `rough' bilinear singular integrals with limited smoothness assumptions. In Chapters 3 and 4 we study the extent to which the sparse theory applies in the setting of operators with a bi- or multi-parameter structure. In particular in Chapter 4 we show that the simplest one- parameter sparse bound (for the dyadic Hardy-Littlewood maximal function) does not directly generalize to the bi-parameter setting. Chapter 2 is based on [1]. Chapter 3 is based on [2] and is joint work with Jill Pipher. Chapter 4 is based on [3] and is joint work with Jos´eConde Alonso, Yumeng Ou, and Guillermo Rey. In Part II we study certain global-in-time Strichartz-type estimates for solutions to the linear n d semiperiodic Schr¨odingerequation (on manifolds of the type R × T ). In Chapter 5 we survey n d the related theory on R and T . In Chapter 6 we discuss some earlier results on R × T and n d then prove a certain generalization on R × T (see Chapter 6 for a precise statement). A large part of Chapter 6 is based on [69]. v vi Acknowledgments This thesis would not have been possible without the generous help and support of my advisor Jill Pipher. I also benefited greatly from discussions with other faculty at Brown, including Jos´e Conde Alonso, Francesco Di Plinio, Benoit Pausader and Sergei Treil. The same can be said of all the students in analysis that I've had the privilege of talking to during my time at Brown: Amalia Culiuc, Milen Ivanov, Spyridon Kakaroumpas, Linhan Li, and Yumeng Ou. vii viii Contents I Sparse Bounds in Harmonic Analysis5 1 A Brief Overview of Sparse Bounds7 2 Sparse Bounds for Rough Bilinear Operators 11 2.0.1 Structure of the Chapter............................ 15 2.0.2 Notation and Definitions............................ 15 2.1 Abstract Sparse Theorem in Multilinear Setting................... 16 2.1.1 Remark on Truncations............................ 18 2.1.2 The Abstract Theorem............................. 19 2.1.3 Some Remarks on Theorem 2.2........................ 21 2.2 Multilinear Calder´on-Zygmund Operators...................... 23 2.2.1 Single-Scale Estimates............................. 25 2.2.2 Cancellation Estimates............................. 28 2.3 Rough Bilinear Singular Integrals........................... 33 2.3.1 Interpolation Lemmas............................. 34 2.3.2 The Sparse Bound............................... 38 2.4 Weighted Estimates.................................. 40 2.4.1 Single Weight - Proof of Corollary 2.2.................... 40 2.4.2 Multiple Weights................................ 42 2.5 Proof of Theorem The Abstract Theorem...................... 44 1 2.5.1 Construction of the Sparse Collection.................... 44 2.5.2 Multiplication Operators........................... 49 3 Sparse Bounds in the Multi-Parameter Setting 53 3.1 Some Difficulties.................................... 54 3.2 An Approach Using Square Functions........................ 56 3.2.1 Remarks on Theorem 3.1........................... 58 3.3 The Lacey-Ou Example................................ 59 3.4 The Bi-Parameter Martingale Transform....................... 62 3.4.1 The Geometric Proof of Theorem 3.1..................... 63 3.5 Bi-Parameter Dyadic Shifts and Singular Integrals................. 67 3.5.1 Definitions.................................... 68 3.5.2 The Sparse Bound............................... 69 3.5.3 Bi-Parameter Singular Integrals........................ 73 3.6 Weighted Estimates for Bi-Parameter Martingale Transform............ 74 3.7 Weighted Estimates for the Shifted Square Function................ 78 3.7.1 Preliminary Results.............................. 79 3.7.2 The Sparse Bound............................... 82 4 A Counterexample for the Strong Maximal Function 93 4.1 Lower bounds for MS and upper bounds for sparse forms............. 96 4.1.1 Lower bound for MS ............................. 99 4.1.2 Upper bound for sparse forms......................... 100 4.2 Construction of the extremal sets........................... 104 4.2.1 Construction of P and the proof of Theorem 4.2.............. 105 4.2.2 Construction of Z ............................... 107 4.2.3 Proof of lemma 4.5 and (Z.5)......................... 109 4.3 Extensions and open questions............................ 114 2 4.3.1 Failure of sparse bound for bi-parameter martingale transform...... 114 4.3.2 Failure of sparse bound in higher dimensions................ 116 4.3.3 Other sparse forms............................... 119 II Semiperiodic Strichartz Etimates 123 n d 5 Strichartz Estimates on R and T 125 5.0.1 Strichartz Estimates on Euclidean Space................... 125 5.0.2 Strichartz Estimates on the Torus...................... 127 6 The Semiperiodic Case 131 6.1 Local Estimates on R × T ............................... 132 n d 6.2 Global Estimates on R × T ............................. 137 6.3 Preliminary Results.................................. 142 6.4 The Decoupling Argument............................... 147 6.4.1 Main Lemmas.................................. 148 6.4.2 Main Argument................................. 150 6.4.3 Proof of Decoupling Lemma 6.7........................ 152 6.5 The -Removal Argument............................... 156 6.5.1 The Local-In-Time Case............................ 156 6.5.2 The Global Case................................ 160 6.6 Some Applications................................... 167 6.6.1 Function Spaces................................ 167 6.6.2 The Quintic Equation on R × T ........................ 169 2 6.6.3 The Cubic Equation on R × T ....................... 176 6.7 Additional Remarks.................................. 178 3 4 Part I Sparse Bounds in Harmonic Analysis 5 Chapter 1 A Brief Overview of Sparse Bounds Over the past several years there has been a lot of activity concerning the sparse domination of various operators arising in harmonic analysis. Given an operator T and suitable test functions n f; g on R one typically shows that there exists a sparse collection of cubes S such that X 1 T f(x) . hfiQ Q(x) Q2S or such that X jhT f; gij ≤ C hfir;Qhgis;QjQj (1.1) Q2S 1 R r 1=r for some 1 ≤ r; s < 1; where hfir;Q = ( jQj Q jfj dx) and hfiQ = hfi1;Q (if T is multilinear one needs to work with a more general multilinear version of this estimate, see below). The sparse collection S is almost disjoint in the following sense: there exists η 2 (0; 1) such that for each Q 2 S there is a subset EQ ⊂ Q such that jEQj ≥ ηjQj, and moreover EQ \ EQ0 = ; for distinct Q; Q0 2 S. The sparse theory offers a new approach to the analysis of many classical (and non-classical) operators in harmonic analysis, and indeed most of the major results in the area were proved within the last five years. We now know that bounds of the type (1.1) hold for a wide variety of operators: smooth and rough Calder´on-Zygmund operators, singular integrals along curves, the 7 spherical maximal function, the variational Carleson operator, the bilinear Hilbert transform, certain Bochner-Riesz multipliers, pseudodifferential operators, singular operators associated to elliptic operators on manifolds, and various discrete analogues of classical operators (this list is far from exhaustive, see for example [53], [48], [4], [6], [19], [1] and the references therein). Sparse bounds typically recover the full range of known strong and weak-type Lp bounds for T , and also yield vector-valued estimates as a corollary. Moreover, a bound of type (1.1) implies a range of quantitative weighted estimates for T with respect to Muckenhoupt and reverse H¨older weight classes, and these bounds are often sharp in terms