New stability results for sequences of metric measure spaces with uniform Ricci bounds from below

The aim of this paper is to provide new stability results for sequences of metric measure spaces (Xᵢ, dᵢ, mᵢ) convergent in the measured Gromov-Hausdorff sense. By adopting the so-called extrinsic approach of embedding all metric spaces into a common one (X, d), we extend the results of Gigli-Mondino-Savar\'e by providing Mosco convergence of Cheeger's energies and compactness theorems in the whole range of Sobolev spaces H^1, p, including the space BV, and even with a variable exponent pᵢ 1,. In addition, building on the results of Ambrosio-Stra-Trevisan, we provide local convergence results for gradient derivations. We use these tools to improve the spectral stability results, previously known for p>1 and for Ricci limit spaces, getting continuity of Cheeger's constant. In the dimensional case N<, we improve some rigidity and almost rigidity results by Ketterer and Cavaletti-Mondino. On the basis of the second-order calculus by Gigli, in the class of RCD (K, ) spaces we provide stability results for Hessians and W^2, 2 functions and we treat the stability of the Bakry-\'Emery condition BE (K, N) and of Ric KI, with K and N not necessarily constant.