Reassessment of the GZK cutoff in the spectrum of UHE cosmic rays in a universe with low photon-baryon ratio

A prediction of standard Big Bang cosmology is that the observed UHECR (ultra-high-energy cosmic rays) spectrum will exhibit a cutoff at the GKZ limit, resulting from interaction with the photons that constitute the cosmic microwave background. We show that for the Quasi-Static Universe (QSU) model, in which photon energy is an invariant in the cosmological reference frame, the photon number density in the universe today is a factor of 10^9 less than in the standard model. As a consequence, the mean free path of UHECRs will exceed the horizon distance of the universe, rendering it essentially transparent to UHECRs. The QSU model therefore predicts that no cutoff will be observed in the UHECR spectrum.