Moose models with vanishing $S$ parameter

Abstract

In the linear moose framework, which naturally emerges in deconstruction models, we show that there is a unique solution for the vanishing of the $S$ parameter at the lowest order in the weak interactions. We consider an effective gauge theory based on $K$ SU(2) gauge groups, $K+1$ chiral fields and electroweak groups $SU(2)_L$ and $U(1)_Y$ at the ends of the chain of the moose. $S$ vanishes when a link in the moose chain is cut. As a consequence one has to introduce a dynamical non local field connecting the two ends of the moose. Then the model acquires an additional custodial symmetry which protects this result. We examine also the possibility of a strong suppression of $S$ through an exponential behavior of the link couplings as suggested by Randall Sundrum metric.

Figures (8)

• Figure 1:
• Figure 2: Graphic representation of the linear moose model with the $m$ link cut described by the lagrangian (\ref{['lagrangian:c']}). The dashed lines represent the identification of the global symmetry groups after weak gauging.
• Figure 3: For $K$ odd, putting one of the $f_i$'s to zero in a reflection invariant model, one is left with a string containing more vector fields than scalars.
• Figure 4: For $K$ even, cutting the central link we are left with two strings, each of them ending with a gauge field.
• Figure 5: The left panel gives a graphic representation of the lagrangian (\ref{['lbess']}) for $a_1=0$, $a_2=a_3$. The right panel gives a graphic representation of the D-BESS model lagrangian (\ref{['lagrangian:2']}). The dash lines represent the identification of the global symmetry groups after the electroweak gauging.