Exotic sources of ultra-high energy cosmic rays

The mystery of UHECR corresponds to the fact that with ordinary astrophysical objects it seems impossible to accelerate them in our galaxy, to avoid the identification of their source if it is in a nearby region and to evade the degrading of their energy if they come from far way. We will consider the alternatives based on non-standard physics which imply topological defects or superheavy particles in the case of a galactic origin, abnormal extragalactic magnetic fields if the source is a nearby astrophysical object, and cosmic strings or non-conventional messengers even with violation of Lorentz invariance if they travel through a long distance.