NON-ABELIAN EFFECTS IN NONLINEAR QUANTUM ELECTRODYNAMICS AND IN Z(0) DECAY INTO 3 PHOTONS

The three-photon decay mode of the neutral weak boson Z0 is studied as an example of a more general class of reactions such as the light by light and the Delbruck scatterings, the splitting of one photon into two under the nuclear electric field and its reverse reaction called the coalescence of photons. All these processes receive contributions - besides the ones due to quarks and leptons - from the W gauge boson in loops. The latter involves the very distinctive non-abelian feature of the standard model through the existence of triple and quadruple couplings between gauge bosons. The W contribution is found to be substantial and may show the (not yet directly tested) fundamental Yang-Mills properties of electroweak theory or reveal non-standard new physics such as the compositeness of the Z0.