Production and signatures of neutral pseudo-Goldstone bosons at the Z0 pole in Technicolor and Extended Technicolor models

The existence of pseudo-Goldstone bosons (PGBs) is a common prediction of almost all non-minimal technicolor and extended technicolor models. In this paper we present a study of the production and decay of neutral PGBs at the Z0 pole. We have expressed the couplings of the PGBs to ordinary particles in a form that is, to a large extent, model independent. This allows to obtain quite a general predictions of the theory for the various production and decay rates. The favorite channel in which neutral PGBs can be produced in Z0 decays is usually represented by the simple Z0 --> P(gamma) decay. The main new result of this paper is an extensive analysis of the various Z0 --> PffBAR decays, where P is a PGB and ffBAR is a fermion pair. The corresponding branching ratios are smaller than 10(-7) for almost all the possible values of the PGB mass, unless some specific theoretical assumptions are introduced. We also discuss the Z0 --> l- l-gamma events with large photon invariant mass, recently observed by the L3 Collaboration at LEP. in the framework of ETC models.