Jacobi fields of the Tanaka-Webster connection on Sasakian manifolds
نویسندگان
چکیده
We build a variational theory of geodesics of the Tanaka-Webster connection ∇ on a strictly pseudoconvex CR manifold M . Given a contact form θ on M such that (M, θ) has nonpositive pseudohermitian sectional curvature (kθ(σ) ≤ 0) we show that (M, θ) has no horizontally conjugate points. Moreover, if (M, θ) is a Sasakian manifold such that kθ(σ) ≥ k0 > 0 then we show that the distance between any two consecutive conjugate points on a lengthy geodesic of∇ is at most π/(2 √ k0). We obtain the first and second variation formulae for the Riemannian length of a curve in M and show that in general geodesics of ∇ admitting horizontally conjugate points do not realize the Riemannian distance.
منابع مشابه
On Para-sasakian Manifolds Satisfying Certain Curvature Conditions with Canonical Paracontact Connection
In this article, the aim is to introduce a para-Sasakian manifold with a canonical paracontact connection. It is shown that φ−conharmonically flat , φ−W2 flat and φ−pseudo projectively flat para-Sasakian manifolds with respect to canonical paracontact connection are all η−Einstein manifolds. Also, we prove that quasi-pseudo projectively flat para-Sasakian manifolds are of constant scalar curvat...
متن کاملSubmanifolds with Harmonic Mean Curvature in Pseudo-hermitian Geometry
We classify Hopf cylinders with proper mean curvature vector field in Sasakian 3-manifolds with respect to the Tanaka-Webster connection.
متن کاملA Basic Inequality for the Tanaka-Webster Connection
For submanifolds tangent to the structure vector field in Sasakian space forms, we establish a Chen’s basic inequality between the main intrinsic invariants of the submanifold namely, its pseudosectional curvature and pseudosectional curvature on one side and the main extrinsic invariant namely, squared pseudomean curvature on the other side with respect to the TanakaWebster connection. Moreove...
متن کاملRicci Curvature Type Lower Bounds for Sub-riemannian Structures on Sasakian Manifolds
Measure contraction properties are generalizations of the notion of Ricci curvature lower bounds in Riemannian geometry to more general metric measure spaces. In this paper, we give sufficient conditions for a Sasakian manifold equipped with a natural sub-Riemannian distance to satisfy these properties. Moreover, the sufficient conditions are defined by the Tanaka-Webster curvature. This genera...
متن کاملOn the pseudohermitian sectional curvature of a strictly pseudoconvex CR manifold
We show that the pseudohermitian sectional curvature Hθ(σ) of a contact form θ on a strictly pseudoconvex CR manifold M measures the difference between the lengthes of a circle in a plane tangent at a point of M and its projection on M by the exponential map associated to the Tanaka-Webster connection of (M, θ). Any Sasakian manifold (M, θ) whose pseudohermitian sectional curvature Kθ(σ) is a p...
متن کامل