Cosmic ray knee and new physics at the TeV scale

Abstract

We analyze the possibility that the cosmic ray knee appearsat an energy threshold where the proton-dark matter cross section becomes large due to new TeV physics. It has been shown that such interactions could break the proton and producea diffuse gamma ray flux consistent with MILAGRO observations.We argue that this hypothesis implies knees that scale with the atomic mass for the different nuclei, asKASKADE data seem to indicate.We find that to explain the change in the spectral index in the flux from E−2.7to E−3.1 the cross section must grow like E0.4+β above the knee, where β = 0.3–0.6 parametrizesthe energy dependence of the age (τ∝E−β) of the cosmic rays reaching the Earth. The hypothesis also requires mbarn cross sections (that could be modelled with TeV gravity) and large densities of dark matter (that could be clumped around the sources of cosmic rays). We argue that neutrinos would also exhibit athreshold at E = (mχ/mp) Eknee ≈ 108 GeV where their interaction with a nucleon becomesstrong. Therefore, the observation at ICECUBE or ANITA of standard neutrino events above this threshold would disprove the scenario.