Prospects for joint cosmic ray and neutrino constraints on the evolution of trans-Greisen-Zatsepin-Kuzmin proton sources

We consider the prospects for future ultrahigh energy cosmic ray and neutrino observations to constrain the evolution of sources producing a proton flux above 10 EeV (1 EeV=1018 eV). We find that strong constraints on the source evolution can be obtained by combining measurements of the cosmic ray proton fraction above 30 EeV with measurement of the neutrino flux at 1 EeV, if neutrinos are predominantly of cosmogenic origin. In the case that interactions in the source environment produce a significant astrophysical neutrino flux, constraints on the source evolution may require measurement of the observed proton fraction, as well as, the neutrino flux at multiple energies, such as 1 EeV and 10 EeV. Finally, we show that fits to current UHECR data favor models which result in a >30 EeV proton fraction and 1 EeV neutrino flux that could realistically be discovered by the next generation of experiments.