Neutron oscillations to parallel world: earlier end to the cosmic ray spectrum?

Present experimental data do not exclude fast oscillation of the neutron n to its degenerate twin from a hypothetical parallel sector, the so called mirror neutron n'. We show that this effect brings about remarkable modifications of the ultrahigh-energy cosmic ray spectrum testable by the present Pierre Auger Observatory (PAO) and Telescope Array (TA) detector, and the future JEM-EUSO experiment. In particular, the baryon non-conservation during UHECR propagation at large cosmological distances shifts the beginning of the GZK cutoff to lower energies, while in the presence of mirror sources it may enhance the spectrum at E > 100 EeV. As a consequence, one can expect a significant reduction of the diffuse cosmogenic neutrino flux.