  Recently, the IceCube collaboration made a big announcement of the first
discovery of high-energy cosmic neutrinos. Their origin is a new interesting
mystery in astroparticle physics. The present multimessenger data may give us
hints of connection to cosmic-ray and/or gamma-ray sources. We look over
possible scenarios for the cosmic neutrino signal, and emphasize the importance
of multimessenger approaches in identifying the PeV neutrino sources and
obtaining crucial clues to the cosmic-ray origin. We also discuss some
possibilities to study neutrino properties and probe new physics.
