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 to a 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 presence of mirror sources it may enhance the spectrum at $E \gtrsim 100$ EeV. As a consequence, a significant reduction of the expected diffuse cosmogenic neutrino flux is predicted.