Cosmology in (2 + 1) -Dimensions, Cyclic Models, and Deformations of M2,1. (AM-121), Volume 121

Do there exist Lorentzian manifolds all of whose light-like geodesics are periodic? A surprising fact is that such manifolds exist in abundance in (2 + 1)-dimensions (though in higher dimensions they are quite rare). This book deals with the deformation theory of M2,1 (which furnishes almost all the known examples of these objects).

Obiectul acestei lucrari este o zona a geometriei lorentziene care nu a fost pana acum mult investigata: Exista varietati lorentziene ale caror geodezii asemanatoare luminii sunt periodice? Un fapt surprinzator este ca astfel de varietati exista din abundenta in (2 + 1) dimensiuni (desi in dimensiuni superioare sunt destul de rare).