Ultra high energy cosmic rays above 1011 GeV: Hints to new physics beyond Standard Model

The observed cosmic ray events above 10¹² GeV are difficult to explain within the context of known physics of propagation of known particles in the Universe and within the standard acceleration mechanisms that are likely to operate in powerful astrophysical objects. Several ideas of possible new physics beyond the Standard Model have been suggested in order to explain these events. The major suggestions are summarized here.