4 II. REVIEW OF THE GD-BESS MODEL The GD-BESS model is a moose model with a [ SU (2)] 2 N ⊗ SU (2)$_{L}$ ⊗ U (1)$_{Y}$ gauge sym- metry, described by the Lagrangian [60]: L = 2 N +1 ∑ i =1 $^{,i}$̸ = N +1 f 2 i Tr[ D$_{µ}$ $_{Σ}$† $_{i}$D$^{µ}$Σ$_{i}$ ] + f 2 $_{0}$Tr[ D$_{µ}$$_{U}$†$_{D}$ $^{µ}$U ] − 1 2˜ g $_{2}$Tr[( F ˜ W $_{µν}$) $^{2}$] − 1 2˜ g ′ $_{2}$Tr[( F ˜ B $_{µν}$) $^{2}$] − 1 2 g 2 i 2 N ∑ i =1 Tr[( F i $_{µν}$) $^{2}$] , (1) where F i µν = ∂$_{µ}$ A i ν − ∂$_{ν}$ A i µ + i [ A$_{µ}$ , A$_{ν}$ ] , i = 0 , . . . 2 N + 1 (2) with A i ≡ A a i τ a 2 , i = 1 , . . . 2 N are the [ SU (2)] 2 N gauge fields, A 0 ≡ ˜ W ≡ ˜ W a τ a 2 and A 2 N +1 ≡ ˜ B ≡ ˜ B τ 3 2 are the SU (2)$_{L}$ ⊗ U (1)$_{Y}$ gauge fields, and the chiral fields Σ$_{i}$ and U have covariant derivatives defined by D$_{µ}$ Σ i = ∂$_{µ}$ Σ i + i A $^{i}$− 1 µ Σ i − i Σ $^{i}$Ai $_{µ}$, i = 1 , . . . 2 N + 1 , i = N + 1 (3) D$_{µ}$U = ∂$_{µ}$U + i ˜ W$_{µ}$ U − iU ˜ B$_{µ}$ (4) f$_{i}$ = $^{f$_{2}$$_{N}$$_{+2}$}$− $_{i}$, g$_{i}$ = $^{g$_{2}$$_{N}$$_{+1}$}$− $_{i}$. (5) The model has two sets of parameters, the gauge coupling constants ˜ g, ˜ g ′ , g$_{i}$, i = 1 , . . . 2 N , and the “link coupling constants” f$_{i}$, i = 1 , . . . 2 N + 1 , i = N + 1. For simplicity, we will impose a reflection invariance with respect to the ends of the moose, getting the following relations among the model parameters The model content in terms of fields and symmetries can be summarized by the moose in Fig. 1. The most peculiar feature is the absence in the Lagrangian given in Eq. (1) of any field connecting the N th and the N + 1 th sites of the moose. This situation was referred to in ref. [39] as “cutting a link”. As it was shown there, this choice guarantees the vanishing of the leading order corrections from new physics to the EW precision parameters; for instance, in ref. [60], the contributions to the ϵ parameters [67–69] as well as the “universal” form factors [26] were calculated, showing that all these contributions are of order m 2 $_{Z}$/ ¯ M $^{2}$, where ¯ M is the mass scale of the lightest new resonance in the theory.