A Tumbling Top-Quark Condensate Model

We propose a renormalizable model with no fundamental scalars which breaks itself in the manner of a “tumbling” gauge theory down to the standard model with a top-quark condensate. Because of anomaly cancellation requirements, this model contains two color sextet fermions (quixes), which are vector-like with respect to the standard model gauge group. The model also has a large number of pseudo-Nambu-Goldstone bosons, some of which can be light. The top-quark condensate is responsible for breaking the electroweak gauge symmetry and gives the top quark a large mass. We discuss the qualitative features and instructive shortcomings of the model in its present form. We also show that this model can be naturally embedded into an aesthetically pleasing model in which the standard model fermion families appear symmetrically. Recently there has been a great deal of interest in the idea[1-4] that the electroweak symmetry of the standard model is broken by a top-quark condensate. This would give a natural explanation for the fact that the top quark has a much larger mass than any of the other quarks and leptons, while simultaneously providing an electroweak symmetry breaking mechanism without a fundamental Higgs scalar. In early versions of this idea, the top-quark condensate was supposed to be induced by a gauge-invariant but non-renormalizable four-fermion interaction Leff ∼ g2 M2 (Q i t) (tQ i) (1) introduced at a scale M which must be larger than the electroweak breaking scale. [Here Qi is the left-handed third generation quark doublet, the i is an SU(2)L index, and t is the right-handed part of the top quark. Color indices are suppressed.] If the coupling g is large enough at the scale M , then a Nambu-Jona-Lasinio (NJL) mechanism[5] will trigger the formation of a top-quark vacuum expectation value (“condensate”)