Distribution-valued Ricci Bounds for Metric Measure Spaces
We will study metric measure spaces (X, d, m) beyond the scope of spaces with synthetic lower Ricci bounds. In particular, we introduce distribution- valued lower Ricci bounds BE_1(\kappa, \infty)
* for which we prove the equivalence with sharp gradient estimates,
* the class of which will be preserved under time changes with arbitrary \psi \in Lip_b(X), and
* which are satisfied for the Neumann Laplacian on arbitrary semi-convex subsets Y \subset X.
In the latter case, the distribution-valued Ricci bound will be given by the signed measure \kappa = k m_Y + l \sigma_{\partial Y} where k denotes a variable synthetic lower bound for the Ricci curvature of X and l denotes a lower bound for the "curvature of the boundary" of Y, defined in purely metric terms.