Clifford systems, harmonic maps and metrics with non-negative curvature

TL;DR

This paper constructs explicit characteristic maps for vector bundles associated with Clifford systems, determines when their sphere bundles admit cross-sections, and applies these results to harmonic maps and metrics with non-negative curvature.

Contribution

It explicitly constructs characteristic maps for bundles from Clifford systems and establishes conditions for sphere bundle cross-sections, extending classical results and constructing non-negatively curved metrics.

Findings

Explicit characteristic maps for m=4 and 8 cases.

Conditions for sphere bundle cross-sections.

Construction of non-negatively curved metrics on specific manifolds.

Abstract

Associated with a symmetric Clifford system $\{P_0, P_1,\cdots, P_{m}\}$ on $\mathbb{R}^{2l}$, there is a canonical vector bundle $\eta$ over $S^{l-1}$. For $m=4$ and $8$, we construct explicitly its characteristic map, and determine completely when the sphere bundle $S(\eta)$ associated to $\eta$ admits a cross-section. These generalize the results in \cite{St51} and \cite{Ja58}. As an application, we establish new harmonic representatives of certain elements in homotopy groups of spheres (cf. \cite{PT97} \cite{PT98}). By a suitable choice of Clifford system, we construct a metric of non-negative curvature on $S(\eta)$ which is diffeomorphic to the inhomogeneous focal submanifold $M_+$ of OT-FKM type isoparametric hypersurfaces with $m=3$.