Min-max theory and Yamabe metrics on conical four-manifolds

We prove existence of Yamabe metrics on four-manifolds possessing finitely-many conical points with ${\mathbb{Z}}_2$-group, using for the first time a min-max scheme in the singular setting. In our variational argument we need to deform continuously regular bubbles into singular ones, while keeping the Yamabe energy sufficiently low. For doing this, we exploit recent positive mass theorems in the conical setting and study how the mass of the conformal blow-up diverges as the blow-up point approaches the singular set.