  We review the particle physics ingredients affecting the normalization,
shape, and flavor composition of astrophysical neutrinos fluxes, such as
different production modes, magnetic field effects on the secondaries (muons,
pions, kaons), and flavor mixing, where we focus on p-gamma interactions. We
also discuss the interplay with neutrino propagation and detection, including
the possibility to detect flavor and its application in particle physics, and
the use of the Glashow resonance to discriminate p-gamma from p-p interactions
in the source. We illustrate the implications on fluxes and flavor composition
with two different models: 1) the target photon spectrum is dominated by
synchrotron emission of co-accelerated electrons and 2) the target photon
spectrum follows the observed photon spectrum of gamma-ray bursts. In the
latter case, the multi-messenger extrapolation from the gamma-ray fluence to
the expected neutrino flux is highlighted.
