Riemannian manifolds with entire Grauert tube are rationally elliptic

It was conjectured by Bott-Grove-Halperin that a compact simply connected Riemannian manifold M with nonnegative sectional curvature is rationally elliptic. We confirm this conjecture under the stronger assumption that M has entire Grauert tube, i.e., M is a real analytic Riemannian manifold that has a unique adapted complex structure defined on the whole tangent bundle TM .