  New physics beyond the electroweak scale may increase weak interaction cross
sections beyond the Standard Model predictions. Such cross sections can be
expected within theories that solve the hierarchy problem of known interactions
with a unification scale in the TeV range. We derive constraints on these cross
sections from the flux of neutrinos expected from cosmic ray interactions with
the microwave background and the non-observation of horizontal air showers. We
also discuss how this limit can be improved by upcoming cosmic ray and neutrino
experiments, and how the energy dependence of the new interactions can be
probed by these experiments.
