Cosmic radiation cutoff at LOW energies?
The energy spectrum of the cosmic radiation (not CMB) is limited on both sides.
I know about the GZK-cutoff at high energies. Basically, the interaction probability for photons of energies above 10^20 eV becomes so high that all have interacted before they can reach us.
But why is there a limit at lower energies? Earth's magnetic field, atmosphere, and/or radiation belt? Perhaps someone can explain that to me.