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Free, publiclyaccessible full text available December 1, 2024

Abstract In 1980 Carleson posed a question on the minimal regularity of an initial data function in a Sobolev space $H^s({\mathbb {R}}^n)$ that implies pointwise convergence for the solution of the linear Schrödinger equation. After progress by many authors, this was recently resolved (up to the endpoint) by Bourgain, whose counterexample construction for the Schrödinger maximal operator proved a necessary condition on the regularity, and Du and Zhang, who proved a sufficient condition. Analogues of Carleson’s question remain open for many other dispersive partial differential equations. We develop a flexible new method to approach such problems and prove that for any integer $k\geq 2$, if a degree $k$ generalization of the Schrödinger maximal operator is bounded from $H^s({\mathbb {R}}^n)$ to $L^1(B_n(0,1))$, then $s \geq \frac {1}{4} + \frac {n1}{4((k1)n+1)}.$ In dimensions $n \geq 2$, for every degree $k \geq 3$, this is the first result that exceeds a longstanding barrier at $1/4$. Our methods are numbertheoretic, and in particular apply the Weil bound, a consequence of the truth of the Riemann Hypothesis over finite fields.more » « less

Abstract We formulate a general problem: Given projective schemes and over a global field
K and aK ‐morphism η from to of finite degree, how many points in of height at mostB have a pre‐image under η in ? This problem is inspired by a well‐known conjecture of Serre on quantitative upper bounds for the number of points of bounded height on an irreducible projective variety defined over a number field. We give a nontrivial answer to the general problem when and is a prime degree cyclic cover of . Our tool is a new geometric sieve, which generalizes the polynomial sieve to a geometric setting over global function fields. 
null (Ed.)Abstract This paper provides a rigorous derivation of a counterexample of Bourgain, related to a wellknown question of pointwise a.e. convergence for the solution of the linear Schrödinger equation, for initial data in a Sobolev space. This counterexample combines ideas from analysis and number theory, and the present paper demonstrates how to build such counterexamples from first principles, and then optimize them.more » « less