Where are Milky Way’s Hadronic PeVatrons?

Observations indicate the existence of natural particle accelerators in the Milky Way, capable of producing PeV cosmic rays (“PeVatrons”). Observations also indicate the existence of extreme sources in the Milky Way, capable of producing gamma-ray radiations above 100 TeV. If these gamma-ray sources are hadronic cosmic-ray accelerators, then they must also be neutrino sources. However, no neutrino sources have been detected. We discuss how we can consistently understand these observations. We introduce a new population-based approach to probe Milky Way hadronic PeVatrons, demanding consistency between PeV-range data on cosmic rays, gamma rays, and neutrinos. Two extreme scenarios are allowed: (1) the hadronic cosmic-ray accelerators and the gamma-ray sources are the same objects, so that neutrino sources exist and improved telescopes can detect them. (2) the hadronic cosmic-ray accelerators and the gamma-ray sources are distinct, so that there are no detectable neutrino sources. We quantify present constraints and future prospects