Despite great progress, the spectrum and chemical composition of ultrahigh-energy cosmic rays remain controversial, and their sources are unknown. Interpretations of data by the Pierre Auger Observatory in Argentina and the Telescope Array in the USA are different and model dependent. Uncertainties due to extrapolations of high-energy hadron interaction models to energies well above the LHC scale can partially explain the observed differences. I'll talk about the advantages of the mixed nuclei composition model of UHECR sources supported by the PAO and the disadvantages compared to their pure proton composition. New phenomena will be considered at E>100 EeV, explaining the differences in the spectra of the northern and southern skies.
B.I. Stepanov Institute of Physics