{ "id": "0704.0808", "version": "v3", "published": "2007-04-05T21:33:13.000Z", "updated": "2008-01-11T00:26:28.000Z", "title": "On a Conjecture of EM Stein on the Hilbert Transform on Vector Fields", "authors": [ "Michael Lacey", "Xiaochun Li" ], "comment": "92 pages, 20+ figures. Final version of the paper. To appear in Memoirs AMS", "categories": [ "math.CA" ], "abstract": "Let $ v$ be a smooth vector field on the plane, that is a map from the plane to the unit circle. We study sufficient conditions for the boundedness of the Hilbert transform \\operatorname H_{v, \\epsilon}f(x) := \\text{p.v.}\\int_{-\\epsilon}^ \\epsilon f(x-yv(x)) \\frac{dy}y where $ \\epsilon $ is a suitably chosen parameter, determined by the smoothness properties of the vector field. It is a conjecture, due to E.\\thinspace M.\\thinspace Stein, that if $ v$ is Lipschitz, there is a positive $ \\epsilon $ for which the transform above is bounded on $ L ^{2}$. Our principal result gives a sufficient condition in terms of the boundedness of a maximal function associated to $ v$. This sufficient condition is that this new maximal function be bounded on some $ L ^{p}$, for some $ 1