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A restricted $2$-plane transform related to Fourier restriction for surfaces of codimension $2$

Spyridon Dendrinos, Andrei Mustaţă and Marco Vitturi

Vol. 18 (2025), No. 2, 475–526
Abstract

We draw a connection between the affine invariant surface measures constructed by P. Gressman (Duke Math. J. 168:11 (2019), 2075–2126) and the boundedness of a certain geometric averaging operator associated to surfaces of codimension 2 and related to the Fourier restriction problem for such surfaces. For a surface given by (ξ,Q1(ξ),Q2(ξ)), with Q1,Q2 quadratic forms on d , the particular operator in question is the 2-plane transform restricted to directions normal to the surface, that is,

𝒯 f(x,ξ) :=|s|,|t|1f(x sQ1(ξ) tQ2(ξ),s,t)dsdt,

where x,ξ d . We show that when the surface is well-curved in the sense of Gressman (that is, the associated affine invariant surface measure does not vanish) the operator satisfies sharp Lp Lq inequalities for p, q up to the critical point. We also show that the well-curvedness assumption is necessary to obtain the full range of estimates. The proof relies on two main ingredients: a characterisation of well-curvedness in terms of properties of the polynomial det (s2Q1 + t2Q2), obtained with geometric invariant theory techniques, and Christ’s method of refinements. With the latter, matters are reduced to a sublevel set estimate, which is proven by a linear programming argument.

Keywords
harmonic analysis, geometric invariant theory, restricted 2-plane transform, $k$-plane transform, Fourier restriction, Kakeya, Mizohata–Takeuchi
Mathematical Subject Classification
Primary: 44A12
Secondary: 14L24, 42B10
Milestones
Received: 16 November 2022
Revised: 26 August 2023
Accepted: 20 October 2023
Published: 5 February 2025
Authors
Spyridon Dendrinos
School of Mathematical Sciences
University College Cork
Cork
Ireland
Andrei Mustaţă
School of Mathematical Sciences
University College Cork
Cork
Ireland
Marco Vitturi
Department of Mathematics
Munster Technological University
Cork
Ireland

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