Stellar-Evolution Limits on Axion Properties

If axions exist, they are copiously produced in hot and dense plasmas, carrying away energy directly from the interior of stars. Various astronomical observables constrain the operation of such anomalous stellar energy-loss channels and thus provide restrictive limits on the axion interactions with photons, nucleons, and electrons. In typical axion models a limit m_a < 0.01 eV is implied. The main arguments leading to this result are explained, including more recent work on the important supernova 1987A constraint.