Abstract. In this paper we give a non-existence theorem for Hopf real hypersurfaces in complex two-plane Grassmannians G 2 (C m+2 ) satisfying the condition that the structure Jacobi operator R ξ commutes with the 3-structure tensors φ i , i = 1, 2, 3.
IntroductionIn the geometry of real hypersurfaces in complex space forms M n (c) Kimura [6] has proved that Hopf real hypersurfaces in a complex projective space P n (C) with constant principal curvatures are locally congruent to of type (A), a tube over a totally geodesic P k (C), of type (B), a tube over a complex quadric Q n−1 , cot 2 2r = n−2, of type (C), a tube over P 1 (C)×P (n−1)/2 (C), cot 2 2r = 1 n−2 and n is odd, of type (D), a tube over a complex two-plane Grassmannian G 2 (C 5 ), cot 2 2r = 3 5 and n = 9, of type (E), a tube over a Hermitian symmetric space SO(10)/U (5), cot 2 2r = 5 9 and n = 15. The notion of Hopf real hypersurfaces means that the structure vector ξ defined by ξ = −JN satisfies Aξ = αξ, where J denotes a Kaehler structure of P n (C), N and A a unit normal and the shape operator of M in P n (C).A Jacobi field along geodesics of a given Riemannian manifold (M, g) is an important role in the study of differential geometry. It satisfies an well-known differential equation which inspires Jacobi operators. The Jacobi operator is defined by (R X (Y ))(p) = (R(Y, X)X)(p), where R denotes the curvature tensor of M and X, Y denote tangent vector fields on M . Then we see that R X is a self-adjoint endomorphism on the tangent space of M and is related to the differential equation, so called Jacobi equation, which is given by ∇ γ (∇ γ Y ) +