Vortices in ionization collisions

We review the concept of quantum vortices and their appearance in ionization collisions. By relaxing the usual geometrical restrictions on the momenta of the final-state, we study these vortices as submanifolds of codimension 2 in the space where the transition matrix element T is defined. In particular, we exemplify their main characteristics by studying the ionization of hydrogen by positron impact. Previous calculation under a collinear geometry for impact energies larger than 270 eV have shown the presence of three isolated vortices. Here we demonstrate that they are produced by a single vortex line intersecting three times the corresponding two-dimensional collinear plane.