Origin of the ankle in the ultrahigh energy cosmic ray spectrum, and of the extragalactic protons below it
Origin of the ankle in the ultrahigh energy cosmic ray spectrum, and of the extragalactic protons below it
The sharp change in slope of the ultrahigh energy cosmic ray (UHECR) spectrum around $1{0}^{18.6}\text{ }\text{ }\mathrm{eV}$ (the ankle), combined with evidence of a light but extragalactic component near and below the ankle and intermediate composition above, has proved exceedingly challenging to understand theoretically, without fine-tuning. We propose a mechanism …