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The IceCube collaboration has reported neutrinos with energies between ~30TeV and a few PeV that are significantly enhanced over the cosmic-ray inducedatmospheric background. Viable high-energy neutrino sources must contain veryhigh-energy and ultra-high energy cosmic rays while efficiently making PeVneutrinos. Gamma-ray Bursts (GRBs) and blazars have been considered ascandidate cosmic-ray accelerators. GRBs, including low-luminosity GRBs, can beefficient PeV neutrino emitters for low bulk Lorentz factor outflows, althoughthe photopion production efficiency needs to be tuned to simultaneously explainultra-high-energy cosmic rays. Photopion production efficiency of cosmic-raysaccelerated in the inner jets of flat spectrum radio quasars (FSRQs) is ~1-10%due to interactions with photons of the broad-line region (BLR), whereas BL Lacobjects are not effective PeV neutrino sources due to the lack of externalradiation fields. Photopion threshold effects with BLR photons suppressneutrino production below ~1 PeV, which imply that neutrinos from other sourceswould dominate over the diffuse neutrino intensity at sub-PeV energies.Reduction of the >> PeV neutrino flux can be expected when curving cosmic-rayproton distributions are employed. Considering a log-parabolic function todescribe the cosmic-ray distribution, we discuss possible implications forparticle acceleration in black-hole jets. Our results encourage a search forIceCube PeV neutrino events associated with gamma-ray loud FSRQs usingFermi-LAT data. In our model, as found in our previous work, the neutrino fluxis suppressed below 1 PeV, which can be tested with increased IceCube exposure.

Photopion Production in Black-Hole Jets and Flat-Spectrum Radio Quasars as PeV Neutrino Sources