Symmetries of null geometry in indefinite Kenmotsu manifolds (Q1949869)

The author investigates some symmetries of null hypersurfaces in indefinite Kenmotsu manifolds tangent to the structure vector field, by particularly paying attention to the local symmetry, semi-symmetry and Ricci semi-symmetry, as well as their relationships with induced connections studied. He shows that locally symmetric and semi-symmetric null hypersurfaces are totally geodesic and parallel. This is also true for Ricci semi-symmetric null hypersurfaces under certain conditions. The local symmetry, semi-symmetry and Ricci semi-symmetry notions are equivalent for a null Einstein hypersurface. By defining an \(\eta\)-Weyl connection the author shows that an induced connection cannot be an \(\eta\)-Weyl connection.