Poincaré and Brunn–Minkowski inequalities on the boundary of weighted Riemannian manifolds

We study a Riemannian manifold equipped with a density which satisfies the Bakry–Émery Curvature-Dimension condition (combining a lower bound on its generalized Ricci curvature and an upper bound on its generalized dimension). We first obtain a Poincaré-type inequality on its boundary assuming that the latter is locally-convex; this generalizes a purely Euclidean inequality of Colesanti, originally derived as an infinitesimal form of the Brunn-Minkowski inequality, thereby precluding any extensions beyond the Euclidean setting. A dual version for generalized mean-convex boundaries is also obtained, yielding spectral-gap estimates for the weighted Laplacian on the boundary. Motivated by these inequalities, a new geometric evolution equation is proposed, which extends to the Riemannian setting the Minkowski addition operation of convex domains, a notion thus far confined to the purely linear setting. This geometric flow is characterized by having parallel normals (of varying velocity) to the evolving hypersurface along the trajectory, and is intimately related to a homogeneous Monge-Ampère equation on the exterior of the convex domain. Using the aforementioned Poincaré-type inequality on the boundary of the evolving hypersurface, we obtain a novel Brunn–Minkowski inequality in the weighted-Riemannian setting, amounting to a certain concavity property for the weighted-volume of the evolving enclosed domain. All of these results appear to be new even in the classical non-weighted Riemannian setting. Faculty of Mathematics, Higher School of Economics, Moscow, Russia. The author was supported by RFBR project 17-01-00662 and DFG project RO 1195/12-1. The article was prepared within the framework of the Academic Fund Program at the National Research University Higher School of Economics (HSE) in 2017-2018 (grant No 17-01-0102) and by the Russian Academic Excellence Project “5-100”. Emails: [email protected], [email protected]. Department of Mathematics, Technion Israel Institute of Technology, Haifa 32000, Israel. Supported by BSF (grant no. 2010288). The research leading to these results is part of a project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 637851). Email: [email protected].