Smooth compact totally geodesic null hypersurfaces (horizons) arise naturally as Cauchy horizons for partial Cauchy hypersurfaces.
Here I outline a recent proof that if they admit an incomplete generator (non-degenerate) then the surface gravity can be normalized to a non-zero constant.
The proof is, in its most technical part, independent of the approach of Isenberg-Moncrief and Bustamante-Reiris. Also the result holds just under the dominant energy condition, i.e. no vacuum assumption is required. If time permits, I shall also outline the proof that they are actually Cauchy horizons bounded on one-side by a region of chronology violation.
(This is joint work with Sebastian Gurriaran, ENS Paris-Saclay)
Ettore Minguzzi (Firenze): A proof of the constancy of surface gravity for non-degenerate compact horizons
