The Lipschitz Kakeya maximal-function conjecture

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Let vv be a Lipschitz map from R2\mathbb R^2 to the unit circle. For a rectangle RR of sufficiently short length, let V⁡R=R∩v−1(EX⁡R)\operatorname V R=R\cap v^{-1}(\operatorname{EX}R), where EX⁡R\operatorname{EX}R denotes the interval of directions determined by RR, and define

M⁡δ,vf(x)=sup⁡∣V⁡R∣≥δ∣R∣1R(x)∣R∣∫R∣f(y)∣ dy.\operatorname M_{\delta,v}f(x)=\sup_{|\operatorname V R|\geq\delta|R|}\frac{\mathbf 1_R(x)}{|R|}\int_R|f(y)|\,dy.

Lipschitz Kakeya maximal-function conjecture. For some 1<p<21<p<2 and some finite NN, for all 0<δ<10<\delta<1 and all Lipschitz vector fields vv, the operator M⁡δ,v\operatorname M_{\delta,v} maps Lp(R2)L^p(\mathbb R^2) to Lp,∞(R2)L^{p,\infty}(\mathbb R^2) with norm at most ≲δ−N\lesssim\delta^{-N}. The known L2L^2 bound has norm ≲δ−1/2\lesssim\delta^{-1/2}, but the asserted subquadratic estimate is not verified in the source.

References

Primary source

Michael Lacey and Xiaochun Li, “On a Conjecture of EM Stein on the Hilbert Transform on Vector Fields”, arXiv:0704.0808 (2008).

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