Multi messenger physics of astrophysical neutrinos and cosmic ray sources

The expected relationship between the observed astrophysical high energy neutrinos and sources of high energy cosmic rays provides useful clues for inferring the required physical properties of their sources, whose specific nature is still debated. On the other hand, the poor positional localization afforded by both of these messengers can be off-set by observations of the gamma-rays co-produced along with the neutrinos, with the spectrum of the gamma-rays also providing important constraints. I will discuss the interplay between these messengers among themselves, as well as various possible candidate astrophysical sources and the prospects for identifying them.