Georgiou, Nikos and Guilfoyle, Brendan
(2017)
*Hopf hypersurfaces in spaces of oriented geodesics.*
Journal of Geometry, 108 (3).
pp. 1129-1135.
ISSN 0047-2468

## Abstract

A Hopf hypersurface in a (para-)Kaehler manifold is a real hypersurface for which one of the principal directions of the second fundamental form is the (para-)complex dual of the normal vector. We consider particular Hopf hypersurfaces in the space of oriented geodesics of a non-flat space form of dimension greater than 2. For spherical and hyperbolic space forms, the space of oriented geodesics admits a canonical Kaehler–Einstein and para-Kaehler–Einstein structure, respectively, so that a natural notion of a Hopf hypersurface exists. The particular hypersurfaces considered are formed by the oriented geodesics that are tangent to a given convex hypersurface in the underlying space form. We prove that a tangent hypersurface is Hopf in the space of oriented geodesics with respect to this canonical (para-)Kaehler structure if and only if the underlying convex hypersurface is totally umbilic. In the case of three dimensional space forms there exists a second canonical complex structure which can also be used to define Hopf hypersurfaces. We prove that in this dimension, the tangent hypersurface of a convex hypersurface in the space form is Hopf if and only if the underlying convex hypersurface is totally umbilic.

Item Type: | Article |
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Additional Information: | Publisher Copyright: © 2017, Springer International Publishing AG. |

Uncontrolled Keywords: | /dk/atira/pure/subjectarea/asjc/2600/2608 |

Departments or Groups: | |

Depositing User: | Admin SSL |

Date Deposited: | 19 Oct 2022 23:02 |

Last Modified: | 07 Jun 2023 18:41 |

URI: | http://repository-testing.wit.ie/id/eprint/3689 |

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