ΔF=1constraints on composite Higgs models with left-right parity

Abstract

We analyze the bounds on the spectrum of composite Higgs models (CHM) that come from flavor observables, by means of simple two-site effective Lagrangians, which incorporate a custodial symmetry and a Left-Right parity and which could also be adopted in further phenomenological studies on CHM. We derive, in particular, an important constraint on the masses of the $(t_L, b_L)$ partners, which does not depend on the flavor structure of the sector beyond the SM. This bound is obtained from the "infrared" contribution to $b \to s\gamma$ induced by the flavor-conserving effective vertex $Wt_Rb_R$. We find that the presence of a custodial symmetry can play a role in protecting this effective coupling and, as a consequence, in attenuating the constraint, which, however, remains of the order of 1 TeV. In addition to this bound, we calculate the constraints from the "ultraviolet" contribution to $b \to s \gamma$, induced by loops of heavy fermions, and to $\epsilon^{'}/\epsilon_K$.