The Quasi Curvature‐Dimension Condition with Applications to Sub‐Riemannian Manifolds

Abstract

AbstractWe obtain the best known quantitative estimates for the Lp‐Poincaré and log‐Sobolev inequalities on domains in various sub‐Riemannian manifolds, including ideal Carnot groups and in particular ideal generalized H‐type Carnot groups and the Heisenberg groups, corank 1 Carnot groups, the Grushin plane, and various H‐type foliations, Sasakian and 3‐Sasakian manifolds. Moreover, this constitutes the first time that a quantitative estimate independent of the dimension is established on these spaces. For instance, the Li‐Yau / Zhong‐Yang spectral‐gap estimate holds on all Heisenberg groups of arbitrary dimension up to a factor of 4.We achieve this by introducing a quasi‐convex relaxation of the Lott‐Sturm‐Villani CD(K, N) condition we call the “quasi curvature‐dimension condition” QCD(Q, K, N). Our motivation stems from a recent interpolation inequality along Wasserstein geodesics in the ideal sub‐Riemannian setting due to Barilari and Rizzi. We show that on an ideal sub‐Riemannian manifold of dimension n, the measure contraction property MCP(K, N) implies QCD(Q, K, N) with Q = 2N − n ≥ 1, thereby verifying the latter property on the aforementioned ideal spaces; a result of Balogh‐Kristály‐Sipos is used instead to handle nonideal corank 1 Carnot groups. By extending the localization paradigm to completely general interpolation inequalities, we reduce the study of various analytic and geometric inequalities on QCD spaces to the one‐dimensional case. Consequently, we deduce that while (strictly) sub‐Riemannian manifolds do not satisfy any type of CD condition, many of them satisfy numerous functional inequalities with exactly the same quantitative dependence (up to a factor of Q) as their CD counterparts. © 2020 Wiley Periodicals LLC