15 may 2018 -- 11:50
Cortona
Abstract.
After a short overview on the (non-equivariant) Yamabe invariant, we introduce the equivariant one. We show that the $S^1$-Yamabe invariant of the $3$-sphere, endowed with the Hopf action, is equal to the (non-equivariant) Yamabe invariant of the $3$-sphere. Moreover, we give a topological upper bound for the $S^1$ -Yamabe invariant of any closed oriented $3$-manifold endowed with a circle action. This is joint work with Bernd Ammann and Mihaela Pilca.