broken by a combination of Dirichlet BCs and scalar VEV (of the U field) to U (1)$_{e.m.}$ on the y = πR brane. In the following of this work, we will study the model defined by the action (8). First of all, we will perform a general analysis of the full 5D theory by the standard technique of the Kaluza-Klein (KK) expansion. Then we will look at the low-energy limit and derive expression for the ϵ parameters; the results will confirm that this is indeed the 5D limit of GD-BESS. Finally, we will make some remarks on the phenomenology of the model in correspondence with two interesting choices for the geometry of the 5 th dimension, that of a flat dimension ( b ( y ) ≡ 1) and that of a slice of AdS$_{5}$ ( b ( y ) = e − 2 $^{ky}$). 9 Since we wish to keep the metric generic for the moment, a convenient strategy is to expand the gauge fields W a L ( R ) M (and the goldstones π $^{a}$) directly in terms of mass eigenstates [65, 66]. So we define: The expansion (13) is written in full generality. A priori , this means that fields with different SU (2) index could be mixed. The index “( j )” labels all the mass eigenstates. This procedure is in fact more general than it is needed; we will see that, with our choice of BCs for the model, we will get three decoupled towers of eigenstates, so that many of the above wave-functions (or constant coefficients in the case of the brane pseudo-scalars) are vanishing. We will require that the wave-functions in eq.(13) form complete sets, and that after substituting the expansion and performing the integration over the extra-dimensional variable y , a diagonal bilinear Lagrangian result, i.e. the fields defined in eq. (13) are the mass eigenstates. These requests lead to an equation of motion plus a set of BCs that the profiles must satisfy. Details on the derivation are given in Appendix A; here we only report the results. IV. EXPANSION IN MASS EIGENSTATES W a $_{L µ}$( x, y ) = ∞ ∑ j =0 f a $_{L j}$( y ) V ( j ) µ ( x ) , W a L $_{5}$( x, y ) = ∞ ∑ j =0 g a $_{L j}$( y ) G ( j $^{)}$( x ) , W a $_{R µ}$( x, y ) = ∞ ∑ j =0 f a $_{R j}$( y ) V ( j ) µ ( x ) , W a R $_{5}$( x, y ) = ∞ ∑ j =0 g a $_{R j}$( y ) G ( j $^{)}$( x ) , π $^{a}$( x ) = ∞ ∑ j =0 c a j G ( j $^{)}$( x ) . (13)