Equivariant min-max theory and the spherical Bernstein problem in ${\mathbb{S}}^4$

We construct an embedded non-equatorial minimal hypersphere in the unit $4$-sphere ${\mathbb{S}}^4$, which provides a new resolution of Chern’s spherical Bernstein problem in ${\mathbb{S}}^4$. The construction is based on our equivariant min-max theory for $G$-invariant minimal hypersurfaces with reduced genus bound, where $G$ is a compact Lie group acting by isometries on a closed Riemannian manifold with $3$-dimensional orbit space. This confirms an assertion made by Pitts-Rubinstein in 1986. We also show the regularity for the solutions of the $G$-equivariant Plateau problem and the $G$-equivariant isotopy area minimization problem.