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An $L^{3/2}$ $\mathrm{SL}_2$ Kakeya maximal inequality

John Green, Terence L. J. Harris and Yumeng Ou

Vol. 19 (2026), No. 7, 1295–1338
Abstract

We prove a special case of the Kakeya maximal function conjecture in ℝ3, with C𝜖δ−𝜖 loss, when the centre lines of the tubes are SL ⁡ 2 lines and the tubes satisfy a 2-dimensional ball condition (equivalent to the Wolff axioms in this case). We show that the exponent p = 3 2 is sharp and that some loss (such as C𝜖δ−𝜖) is necessary, even in the SL ⁡ 2 case where the δ-tubes have δ-separated directions and the cardinality of the tube family is maximal ( ∼ δ−2).

The SL ⁡ 2 Kakeya maximal inequality is deduced from an L3∕2 inequality for restricted families of projections onto planes. A related L3∕2−𝜖 inequality is also derived for restricted projections onto lines, and an application is given to generic intersections of sets in ℝ3 with “light rays” and “light planes”.

Keywords
Besicovitch set, Kakeya maximal function, restricted projections
Mathematical Subject Classification
Primary: 28A78, 28A80
Milestones
Received: 21 June 2024
Revised: 6 May 2025
Accepted: 19 September 2025
Published: 18 September 2026
Authors
John Green
Mathematics Institute
University of Warwick
Coventry
United Kingdom
Terence L. J. Harris
Department of Mathematics
University of Wisconsin-Madison
Madison, WI
United States
Yumeng Ou
Department of Mathematics
University of Pennsylvania
Philadelphia, PA
United States

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