Abstract
A theorem of L. Caffarelli implies the existence of a map, pushing forward a source Gaussian measure to a target measure which is more log-concave than the source one, which contracts Euclidean distance (in fact, Caffarelli showed that the optimal-transport Brenier map T opt is a contraction in this case). We generalize this result to more general source and target measures, using a condition on the third derivative of the potential, by providing two different proofs. The first uses a map T, whose inverse is constructed as a flow along an advection field associated to an appropriate heat-diffusion process. The contraction property is then reduced to showing that log-concavity is preserved along the corresponding diffusion semi-group, by using a maximum principle for parabolic PDE. In particular, Caffarelli’s original result immediately follows by using the Ornstein–Uhlenbeck process and the Prékopa–Leindler Theorem. The second uses the map T opt by generalizing Caffarelli’s argument, employing in addition further results of Caffarelli. As applications, we obtain new correlation and isoperimetric inequalities.
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Y.-H. Kim and E. Milman were partially supported by the Institute for Advanced Study through NSF Grant DMS-0635607. Y.-H. Kim is also supported by Canadian NSERC discovery Grant 371642-09. E. Milman is also supported by ISF, GIF and the Taub Foundation (Landau Fellow).
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Kim, YH., Milman, E. A generalization of Caffarelli’s contraction theorem via (reverse) heat flow. Math. Ann. 354, 827–862 (2012). https://doi.org/10.1007/s00208-011-0749-x
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DOI: https://doi.org/10.1007/s00208-011-0749-x