  While propagating from their source to the observer, ultrahigh energy cosmic
rays interact with cosmological photon backgrounds and generate to the
so-called "cosmogenic neutrinos". Here we study the parameter space of the
cosmogenic neutrino flux given recent cosmic ray data and updates on plausible
source evolution models. The shape and normalization of the cosmogenic neutrino
flux are very sensitive to some of the current unknowns of ultrahigh energy
cosmic ray sources and composition. We investigate various chemical
compositions and maximum proton acceleration energies E_p,max which are allowed
by current observations. We consider different models of source evolution in
redshift and three possible scenarios for the Galactic to extragalactic
transition. We summarize the parameter space for cosmogenic neutrinos into
three regions: an optimistic scenario that is currently being constrained by
observations, a plausible range of models in which we base many of our rate
estimates, and a pessimistic scenario that will postpone detection for decades
to come. We present the implications of these three scenarios for the detection
of cosmogenic neutrinos from PeV to ZeV (10^14-21 eV) with the existing and
upcoming instruments. In the plausible range of parameters, the narrow flux
variability in the EeV energy region assures low but detectable rates for
IceCube (0.06-0.2 neutrino per year) and the Pierre Auger Observatory
(0.03-0.06 neutrino per year), and detection should happen in the next decade.
If EeV neutrinos are detected, PeV information can help select between
competing models of cosmic ray composition at the highest energy and the
Galactic to extragalactic transition at ankle energies. With improved
sensitivity, ZeV neutrino observatories, such as ANITA and JEM-EUSO could
explore and place limits on the maximum acceleration energy.
