Diffuse neutrino flux from blazars via cosmic-ray propagation in extragalactic medium

The origin of the cosmic neutrino signal measured by IceCube is still unknown. A general correlation between the sources of high-energy γ-ray sources with IceCube neutrinos is expected since hadronic interactions are the crucial precursors of both messengers at such high energies. Blazars dominate the extragalactic γ-ray sky. However, neutrinos originating from inside the blazar jets cannot account for more than ∼ 30% of the diffuse flux. We study ultrahigh-energy cosmic-ray contribution to the diffuse flux through photopion interactions on cosmic background photons. The extragalactic background light, consisting of IR/UV/optical photons require a proton energy threshold of E_th^{p, π} ≈ 10¹⁷ eV for pion production. The latter can yield PeV neutrinos. We analyze the total contribution from resolved and unresolved blazars by using a luminosity-dependent density evolution of blazars. The latest Fermi-LAT 4LAC catalog sheds light on the redshift distribution of the diffuse neutrino flux for resolved γ-ray blazars.