Semi-parallelism of normal Jacobi operator for Hopf hypersurfaces in   complex two-plane Grassmannians
  It is proved the non-existence of Hopf hypersurfaces in $G_{2}({\Bbb C}^{m+2})$, $m \geq 3$, whose normal Jacobi operator is semi-parallel, if the principal curvature of the Reeb vector field is non-vanishing and the component of the Reeb vector field in the maximal quaternionic subbundle ${\frak D}$ or its orthogonal complement ${\frak D}^{\bot}$ is invariant by the shape operator. 
Konstantina Panagiotidou and Mukut Mani Tripathi
math.DG