Symmetry breakdown and coupling constants of leptons

Based on a new approach to symmetries of the fundamental interactions we deal, in this paper, with the electroweak interactions of leptons. We show that the coupling constants, arising in the way leptons are coupled to intermediate bosons, can be understood as parameters associated to the breakdown of SU(2) and parity symmetries. The breakdown of both symmetries is characterized by a new parameter (the asymetry parameter) of the electroweak interactions. This parameter gives a measure of the strength of breakdown of symmetries. We analyse the behaviour of the theory for three values of this parameter. The most relevant value is the one for which only the electromagnetic interactions do not break parity (the maximally allowed left-right asymetric theory). Maximamally allowed parity asymmetry is a requirement that is met for a value of Weinberg's theta-angle that is quite close to the experimental value of this parameter.

NEW TENSOR INTERACTIONS IN μ-DECAY

The most general form of Hamiltonian for the muon decay is presented. We assume that it arises as a result of the exchange of intermediate bosons with a momentum q and naturally should depend on this momentum. That allows us to introduce two additional coupling constants for the tensor interactions which give rise to new parameters in the energy spectrum of positrons. The experimental consequences of such a generalization are discussed.

The award of medals by the President, Lord Porter, O.M., at the Anniversary Meeting, 30 November 1990

The Copley Medal is awarded to Professor A. Salam, K.B.E., F.R.S., in recognition of his work on the symmetries of the laws of nature, and especially the unification of the electromagnetic and weak forces. Professor Salam has made outstanding and influential contributions to elementary particle theory over a period of 40 years. His early work included the completion of Dyson's proof of the renormalization of quantum electrodynamics, and his work on parity violation, dispersion relations and SU(3) invariance. This work contributed greatly to the development of elementary particle theory, but his major contribution was the proposal, in parallel with S. Weinberg, of the electroweak theory, unifying quantum electrodynamics with the weak interactions between atomic particles. That theory, the first to bring together the theories of the atomic forces, received spectacular confirmation through the discovery at CERN in 1983 of W + and Z intermediate bosons.