Neutron β-decay as the origin of IceCube's PeV (anti)neutrinos

Motivated by the indications of a possible deficit of muon tracks in the first three-year equivalent dataset of IceCube we investigate the possibility that the astrophysical (anti)neutrino flux (in the PeV energy range) could originate from \beta-decay of relativistic neutrons. We show that to accommodate IceCube observations it is necessary that only about 1% to 10% of the emitted cosmic rays in the energy decade 10^{8.5} \alt E_{CR}/GeV \alt 10^{9.5}$, yielding antineutrinos on Earth (10^{5.5} \alt E_{\bar \nu}/GeV \alt 10^{6.5}), are observed. Such a strong suppression can be explained assuming magnetic shielding of the secondary protons which diffuse in extragalactic magnetic fields of strength 10 \alt B/nG \alt 100 and coherence length \alt Mpc.