Constraints on Z′ couplings in 331 models from flavor changing neutral currents.

J. M. CABARCAS; D.GÓMEZ DUMM; R. MARTINEZ

Águas de Lindóia, Sao Paulo, Brasil.

Congreso; XXVIII Encontro Nacional de Física de Partículas Campos; 2007

Sociedade Brasilera de Física.

The so-called “331” models are built as an extension of the Standard Model (SM), having an enlarged gauge symmetry group SU(3)C x SU(3)L x U(1)X. In these theories one expects the presence of a new neutral gauge boson Z′ which, in general, gives rise to flavor changing neutral currents (FCNC) already at the tree level. In this work we have taken into account one of the simplest versions of the available 331 theories,which does not include quarks with exotic charges. Within this framework, we have studied the admissible range for the model parameters in order to be compatiblewith recent experimental data. We have concentrated on observables that could reveal the presence of tree level FCNC in the down quark sector, in particular, considering
S = 2 and
B = 2 neutral currents. Observables like the mass difference MKL −MKs are highly suppressed in the SM, where they appear to be nonzero only due to one-loop contributions, and therefore impose severe constraints to the couplings of the new Z′ boson to the usual fermions. In our analysis we consider the Z′ mass as a varying parameter, and analyze the allowed range for the angles and phases of the down quark mixing matrix Vd L . Finally we study the lower bounds on the Z′ mass taking into account a standard ansatz for the quark mixing matrices.