They are normalized to Tr T $^{α}$T β = δ $^{αβ}$. In this basis 5 , which decomposes into ( 2 , 2 ) ⊕ ( 1 , 1 ) under SU (2)$_{L}$ × SU (2)$_{R}$, reads where the first (second) subscript ± , 0 corresponds to T 3 L = ± 1 $_{2}$, 0 ( T 3 R = ± 1 $_{2}$, 0), respectively. Appendix B: KK expansion in the presence of boundary Majorana masses Let us consider the effect on the KK expansion of a bulk fermion ψ with a UV localized Majorana mass term and then satisfying the UV boundary condition The corresponding KK expansion can be written where the 4D fields are assumed to obey a Majorana equation If we insert these expansions in the 5D equations of motion and use the 4D Majorana equations, we get a system of coupled differential equations The solution of this system of equations can be obtained using standard techniques (decou- pling by iteration and use of the first order equation to obtain the second solution), θ$_{ij}$ψ c $_{iR}$ψ$_{jR}$ + h . c ., (B1) ψ$_{iL}$ ( x, R ) + θ † $_{ij}$ψ c $_{jR}$( x, R ) = 0 . (B2) ψ$_{iL}$ ( x, z ) = ∑ n g$_{in}$ ( z ) ξ$_{n}$ ( x ) , ψ$_{iR}$ ( x, z ) = ∑ n f$_{in}$ ( z ) ¯ ξ$_{n}$ ( x ) , (B3) i ¯ σ $^{µ}$∂$_{µ}$ ξ$_{n}$ − m$_{n}$ ¯ ξ$_{n}$ = 0 , iσ $^{µ}$∂$_{µ}$ ¯ ξ$_{n}$ − m ∗ $_{n}$ξ$_{n}$ = 0 . (B4) f ′ in + m$_{n}$g$_{in}$ − c$_{i}$ + 2 z f$_{in}$ = 0 , (B5) g ′ in − m ∗ $_{n}$f$_{in}$ + c$_{i}$ − 2 z g$_{in}$ = 0 . (B6) g$_{in}$ ( z ) = z 5 / 2 ( A$_{in}$J$_{c}$$_{i}$$_{+1}$$_{/}$$_{2}$ ( | m$_{n}$ | z ) + B$_{in}$Y$_{c}$$_{i}$$_{+1}$$_{/}$$_{2}$ ( | m$_{n}$ | z ) ) , (B7) f$_{in}$ ( z ) = m$_{n}$ | m$_{n}$ | z 5 / 2 ( A$_{in}$J$_{c}$$_{i}$ − 1 / $_{2}$( | m$_{n}$ | z ) + B$_{in}$Y$_{c}$$_{i}$ − 1 / $_{2}$( | m$_{n}$ | z ) ) . (B8) 33 Q = 1 √$_{2}$     q$_{++}$ − q −− iq$_{++}$ + iq −− − iq$_{+}$ − + iq − + q$_{+}$ − + q − + √$_{2}$$_{q}$$_{00}$    $^{,}$ (A7)