Dynamical Electroweak Symmetry Breaking

We review the status of and recent developments in dynamical electroweak symmetry breaking, concentrating on the ideas of technicolour and top quark condensates. The emphasis is on the essential physical ideas and experimental implications rather than on detailed mathematical formalism. After a general overview of the subject, we give a first introduction to technicolour, and extended technicolour, illustrating the ideas with a simple (unrealistic) model. Then we review the progress that has been made with enhancing the technicolour condensate, using the Schwinger-Dyson gap equation. The discussion includes the so-called walking technicolour and strong extended technicolour approaches. We then turn to the experimental prospects of technicolour models, including longitudinal gauge boson scattering experiments at the LHC, the detection of pseudo-Goldstone bosons and the hints about electroweak symmetry breaking which comes from precision measurements at LEP. We also discuss a low-scale technicolour model, which has experimental signatures at LEP and the Tevatron. Finally we turn to the idea of the top quark condensate. After reviewing the basic ideas of this approach, we turn to some extensions of these ideas involving the idea of fourth family condensates, and the role of irrelevant operators. This revised version appears in Reports on Progress in Physics 58 (1995) 263. e-mail address [email protected]