content_image/349246.jpg content_image/349245.jpg content_image/349244.jpg content_image/349243.jpg
and 

where a “0” entry means ≲ 10 − $^{2}$, and the order of charge − 1 leptons is τ, T $^{1}$, T $^{2}$. These values are in good agreement with the expectations from degenerate bi-doublets [33] (the small deviations, with no consequence at the LHC, are due to the heavy modes with masses ≳ 3 TeV). As we see, all four new leptons decay into taus 100 % of the time, N → W $^{+}$τ , Y → W − τ , T 1 → Zτ and T 2 → Hτ . 

<img src='content_image/349246.jpg'>

The new leptons are produced in pairs at the LHC. Single production in association with a τ is suppressed because the off-diagonal couplings ¯ τF V , with F the new lepton and V = W, Z , are small [55]. Drell-Yan pair production results in different final states 

from W exchange, 

from photon and Z exchange, whereas 

<img src='content_image/349245.jpg'>

<img src='content_image/349244.jpg'>

<img src='content_image/349243.jpg'>

only proceeds through Z exchange. These signals are difficult to disentangle from the back- ground because tau leptons must be reconstructed, but the relative lightness of these new leptons and their very characteristic decay channels help to search for them. A dedicated analysis, that is currently under way, is required to fully assess the LHC reach for vector-like leptonic resonances as predicted in this class of models. (See [56] for generic decay channels.) 

## VI. CONCLUSIONS 

Models with warped extra dimensions provide a neat solution to the hierarchy problem. In this context, models of gauge-Higgs unification in warped extra dimensions are among the most natural models of EWSB, realizing in a calculable way the old idea of composite Higgs. Furthermore, they also offer a rationale for the flavor structure in the quark sector. Mass hierarchies and hierarchical mixing angles are naturally generated by wave function 

