Dynamical electroweak symmetry breaking

Some new developments in dynamical electroweak symmetry are reviewed. After summarizing a few of the features of the standard electroweak model and the basics of technicolor theories, recent ideas designed to produce realistically large quark and lepton masses are described. The common feature is high-momentum enhancement - the observation that technicolor theories can naturally contain much more ''action'' at energies well above the weak scale than would be expected if they were simply scaled-up versions of QCD. The original idea is called walking and there is another, closely related possibility. Before reviewing this work, dynamical symmetry breaking in some simpler models - a quenched U(1) theory in four dimensions, and both a U(1) theory and QCD in three dimensions - is described. All the work described here relies on the ladder expansion of the gap equation governing the breaking. Recent studies, pointing to the possibility that this expansion may be sufficiently convergent, even when the couplings are large enough to trigger dynamical breaking, are summarized. Constraints imposed on theories of dynamical symmetry breaking by the increasingly precise tests of the standard model are also summarized. The conclusion includes a listing of some recent work on technicolor model building, some of which makes use of the high momentum enhancement ideas described here. (author). 71 refs, figs