Possible Explanation for $E>{10}^{20}$ eV Air Showers with Flavour-Changing Neutral Currents

Air showers observed with $E>{10}^{20}$ eV pose a problem since protons at such energies cannot survive a long journey through the 2.7 K microwave background. It is suggested that they are initiated instead by neutrinos which become strongly interacting through exchanges of gauge bosons associated with generation-changing neutral currents, a suggestion which is supported by calculations in a dualized standard model recently proposed. In turn, the suggestion bounds the mass of the gauge bosons and gives estimates for the branching ratios of FCNC s, c, b, and t meson decays which are accessible to experiments now being planned.