Date/heure
17 novembre 2015
14:00 - 15:00
Oratrice ou orateur
Stephan Suhr
Catégorie d'évènement Séminaire de géométrie différentielle
Résumé
Guillemin calls a compact Lorentzian $3$-manifold « Zollfrei » if the geodesics flow on the nonzero lightlike vectors induces a fibration by circles (especially all lightlike geodesics are closed). He conjectured that these metric can only exist on $3$-manifolds covered by $S^2times S^1$. I will explain counterexamples on every nontrivial circle bundle over a closed surface. If time permits I will discuss what additional assumptions imply the conjecture and hint at what is the right conjecture in the general case.