Independence of synthetic Curvature Dimension conditions on transport distance exponent

Abstract

The celebrated Lott-Sturm-Villani theory of metric measure spaces furnishes synthetic notions of a Ricci curvature lower bound $K$ joint with an upper bound $N$ on the dimension. Their condition, called the Curvature-Dimension condition and denoted by $\mathrm{CD}(K,N)$, is formulated in terms of a modified displacement convexity of an entropy functional along $W_2$-Wasserstein geodesics. We show that the choice of the squared-distance function as transport cost does not influence the theory. By denoting with ${\mathrm{CD}}_p(K,N)$ the analogous condition but with the cost as the $p^{th}$ power of the distance, we show that ${\mathrm{CD}}_p(K,N)$ are all equivalent conditions for any $p>1$ -- at least in spaces whose geodesics do not branch. We show that the trait d'union between all the seemingly unrelated ${\mathrm{CD}}_p(K,N)$ conditions is the needle decomposition or localization technique associated to the $L^1$-optimal transport problem. We also establish the local-to-global property of ${\mathrm{CD}}_p(K,N)$ spaces.