Extrinsic geometry of the Gromoll-Meyer sphere

TL;DR

This paper investigates the geometry of the Gromoll-Meyer sphere, identifying metrics with nonnegative curvature and Einstein properties, and constructs special foliations and hypersurfaces with positive Ricci and quasi-positive sectional curvature.

Contribution

It introduces new geometric structures on quotients related to the Gromoll-Meyer sphere, including isoparametric foliations and transnormal systems with specific curvature properties.

Findings

Identifies metrics on Sp(2) with nonnegative sectional curvature and Einstein metrics.

Constructs a homogeneous isoparametric foliation with hypersurfaces diffeomorphic to Sp(2).

Creates a transnormal system with hypersurfaces diffeomorphic to the Gromoll-Meyer sphere.

Abstract

Among a family of 2-parameter left invariant metrics on Sp(2), we determine which have nonnegative sectional curvatures and which are Einstein. On the quotiente $\widetilde{N}^{11}=(Sp(2)\times S^4)/S^3$, we construct a homogeneous isoparametric foliation with isoparametric hypersurfaces diffeomorphic to Sp(2). Furthermore, on the quotiente $\widetilde{N}^{11}/S^3$, we construct a transnormal system with transnormal hypersurfaces diffeomorphic to the Gromoll-Meyer sphere $\Sigma^7$. Moreover, the induced metric on each hypersurface has positive Ricci curvature and quasi-positive sectional curvature simultaneously.