Composite models of weak gauge bosons

Abstract

Composite models of quarks, leptons and weak bosons are reviewed. It is shown that they can reproduce the low energy results of the Standard Weinberg-Salam Model of electroweak interactions. The consequences of assuming composite W and Z bosons are examined and many new particles are predicted, including excited W and Z states and their pseudoscalar partners. Estimates of the masses and decay widths of these particles are given. It is also shown that coloured weak bosons may exist in the energy range 100-200 GeV. The decays of a composite Z boson are studied in detail using both a potential model and an effective Lagrangian approach. It is found that the width is likely to be significantly different from that of the elementary Z of the Standard Model, In particular there are additional contributions to the decays Z → qqg and Z → ggg which are likely to affect the total Z width by an appreciable amount. The decay of the Z into hypercoloured particles is also examined and it is found that the width is likely to exceed greatly the current experimental bound. It is concluded that the W and Z bosons are likely to be elementary particles because if they were composite their decay widths would be much greater than is found experimentally, unless of course their internal dynamics are quite unlike the model which has been employed.