The extended BESS model: bounds from precision electroweak measurements☆

Abstract We present an effective lagrangian parameterization describing scalar, vector and axial-vector bound states, originating from a strong breaking of the electroweak symmetry, based on the global symmetry SU(N)L ⊗ SU(N)R. In this approach vector and axial-vector bound states are gauge bosons associated to a hidden SU(N)L ⊗ SU(N)R symmetry. After the gauging of the electroweak symmetry, the corrections to the self-energies of the standard model gauge bosons are calculated and bounds on the parameter space of the model arising from precision measurements are studied. The self-energy corrections arise from spin-one mixings, pseudogoldstone loops, pseudogoldstone spin-one loops, and tadpole terms. The one-loop terms tend to decrease both isospin conserving and isospin violating corrections. Careful calculation for standard SU(8) QCD-scaled technicolor shows that strictly this model (which has, however, serious theoretical difficulties on its own) is still marginally allowed at present experimental precision.