Searches for new particle physics by methods of classical and neutrino astronomy

Selected astrophysical methods for testing particle-physics models are reviewed. Stellar structure and evolution constrain additional channels of energy loss and transport; high-energy photon propagation probes photon mixing with new particles and modifications of electron-positron pair production; large-volume neutrino telescopes are used to search for magnetic monopoles, neutrinos from superheavy dark-matter decay, and non-standard neutrino propagation. Recent applications of these methods are discussed, involving the tip of the red-giant branch in the color-luminosity diagram, gamma-ray burst 221009A, and data from the Baikal Gigaton Volume Detector (Baikal-GVD) and the IceCube experiment. In each case, particle-physics parameters are inferred through a forward model that accounts for the response to new physics, propagation, detection, and nuisance parameters.