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math.DG2025
On the parity of the Betti numbers of 3-manifolds with a parallel vector field
Emmanuel Gnandi, Raymond A. Hounnonkpe
The question of whether a closed, orientable manifold can admit a nontrivial vector field that is parallel with respect to some Riemannian metric is a classical problem in Differen…
gr-qc2025
Compact Cauchy horizons admit constant surface gravity
Raymond A. Hounnonkpe, Ettore Minguzzi
We prove that in any spacetime dimension and under the null energy condition, every totally geodesic connected smooth compact null hypersurface (hence every compact Cauchy horizon)…
math.DG2025
Riemannian flow techniques on totally geodesic null hypersurfaces
Manuel Gutiérrez, Raymond A. Hounnonkpe
We study the influence of the existence of totally geodesic null hypersurface on the properties of a Lorentzian manifold. By coupling the rigging technique with the existence of a…