Enforcing strongTandPconservation

The derivation of the properties of the axion which results from an extended weak-electromagnetic symmetry is discussed in some detail. A brief review of the experimental difficulties with a light axion is given. The possibility of a heavy axion, which at first would seem to offer a way out of the problem, is shown to lead to an unacceptable distortion of the pseudoscalar mass spectrum. Other reasonable generalizations of the axion scheme are investigated. These do not, on fairly general grounds, seem to offer a resolution of the problem. Two non-axion solutions (i) $m_u=0\mathrm{}$ and (ii) strong dynamical rejection of $T$- and $P$-violating phases are studied. However, there is no clear evidence for them and some (mild) evidence against them. Finally, other non-axion solutions are mentioned.