Abstract: The Universe is a natural laboratory for us to investigate physics. Neutrinos of cosmic origin are an excellent messenger exploring astronomy, cosmology and particle physics, for they are tiny, neutral and weakly-interacting, which leads to undeflected and nearly unscathed travel across the Universe to Earth from their sources. They are an important piece in solving several significant open questions in physics such as the mystery of cosmic ray accelerators, as high-energy cosmic neutrinos play the role of a smoking-gun signal of hadronic interactions of cosmic rays, and the nature of dark matter as neutrinos can be produced in dark matter annihilation or decay, providing an indirect signature.
The IceCube experiment discovered TeV-PeV neutrinos of astrophysical origin with an energy flux comparable to that of gamma rays and cosmic rays. One mission that comes afterwards is to identify where those neutrinos come from and how they are produced. I will discuss the search for their astrophysical sources, emphasizing the efforts to identify sources in our Galaxy from candidates pulsar wind nebulae and X-ray binaries with IceCube data. Like atmospheric neutrinos, the beam of cosmic neutrinos provides us with excellent opportunities to study physics beyond the standard model, e.g. dark matter annihilation and decay. The indirect searches of dark matter will be discussed with a focus on a new computation of neutrino signals from dark matter accumulated in multiple celestial environments.