Diffuse Neutrino Intensity from the Inner Jets of Active Galactic
  Nuclei: Impacts of External Photon Fields and the Blazar Sequence
  We study high-energy neutrino production in inner jets of radio-loud active
galactic nuclei (AGN), taking into account effects of external photon fields
and the blazar sequence. We show that the resulting diffuse neutrino intensity
is dominated by quasar-hosted blazars, in particular, flat spectrum radio
quasars, and that PeV-EeV neutrino production due to photohadronic interactions
with broadline and dust radiation is unavoidable if the AGN inner jets are
ultrahigh-energy cosmic-ray (UHECR) sources. Their neutrino spectrum has a
cutoff feature around PeV energies since target photons are due to Ly$\alpha$
emission. Because of infrared photons provided by the dust torus, neutrino
spectra above PeV energies are too hard to be consistent with the IceCube data
unless the proton spectral index is steeper than 2.5, or the maximum proton
energy is $\lesssim100$ PeV. Thus, the simple model has difficulty in
explaining the IceCube data. For the cumulative neutrino intensity from blazars
to exceed $\sim{10}^{-8}~{\rm GeV}~{\rm cm}^{-2}~{\rm s}^{-1}~{\rm sr}^{-1}$,
their local cosmic-ray energy generation rate would be $\sim10-100$ times
larger than the local UHECR emissivity, but is comparable to the averaged
gamma-ray blazar emissivity. Interestingly, future detectors such as the
Askaryan Radio Array can detect $\sim0.1-1$ EeV neutrinos even in more
conservative cases, allowing us to indirectly test the hypothesis that UHECRs
are produced in the inner jets. We find that the diffuse neutrino intensity
from radio-loud AGN is dominated by blazars with gamma-ray luminosity of
$\gtrsim10^{48}~{\rm erg}~{\rm s}^{-1}$, and the arrival directions of their
$\sim1-100$ PeV neutrinos correlate with the luminous blazars detected by
Fermi.
