Production and signatures of neutral pseudo-Goldstone bosons at the Z0 pole in technicolor and extended technicolor models

Abstract

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 Z 0 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 Z 0 decays is usually represented by the simple Z 0 → Pγ decay. The main new result of this paper is an extensive analysis of the various Z 0 → P ƒƒ decays, where P is a PGB and ƒƒ 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 Z 0 → l + l − γ events with large photon invariant mass, recently observed by the L3 Collaboration at LEP, in the framework of ETC models.