ABSTRACT
Many of the most interesting theoretical speculations about physics beyond the standard model involve energy scales that cannot be probed in terrestrial laboratory experiments. Fortunately, the Heavenly Laboratory, in the guise of the early Universe and various contemporary astrophysical sites, has proven to be invaluable in studying physics in regimes beyond the reach of terrestrial laboratories. The axion is a prediction of the most elegant solution to the strong-CP problem of quantum chromodynamics (QCD), Peccei-Quinn symmetry. QCD is a remarkable theory and is almost universally believed to be the theory of the strong interactions. Owing to the existence of non-trivial, vacuum gauge configurations, non-Abelian gauge theories have a rich vacuum structure. The rather uncomplicated life of a star involves only the simple struggle to regain the state of nuclear statistical equilibrium (NSE) lost during primordial nucleosynthesis. The most dramatic example of the importance of neutrino cooling is SN 1987A.
