Almost-Riemannian manifolds do not satisfy the curvature-dimension condition

The Lott-Sturm-Villani curvature-dimension condition $$ provides a synthetic notion for a metric measure space to have curvature bounded from below by K and dimension bounded from above by N. It was proved by Juillet (Rev Mat Iberoam 37(1), 177-188, 2021) that a large class of sub-Riemannian manifolds do not satisfy the $$ condition, for any $$ and $$ . However, his result does not cover the case of almost-Riemannian manifolds. In this paper, we address the problem of disproving the $$ condition in this setting, providing a new strategy which allows us to contradict the one-dimensional version of the $$ condition. In particular, we prove that 2-dimensional almost-Riemannian manifolds and strongly regular almost-Riemannian manifolds do not satisfy the $$ condition for any $$ and $$ .