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On the Flavor Problem in Strongly Coupled Theories - THEP Mainz

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2.3. Profiles of Gauge Bosons 57<br />

see Table 2.1. But <strong>the</strong> A5 component will also not propagate <strong>in</strong> <strong>the</strong> unitary gauge,<br />

ξ → ∞, which is <strong>the</strong> exact behavior of a Goldstone boson and confirms <strong>the</strong>refore our<br />

<strong>the</strong> f<strong>in</strong>d<strong>in</strong>gs of Section 2.2, that A5 can be considered to be <strong>the</strong> holographic dual of<br />

a Goldstone boson. In this limit, <strong>the</strong> KK excitations of <strong>the</strong> vector fields will eat <strong>the</strong><br />

KK modes of <strong>the</strong> A5s and become massive, compare [62]. The behavior of <strong>the</strong> zero<br />

modes will depend on <strong>the</strong> BCs.<br />

The propagator is symmetric <strong>in</strong> t and t ′ and a viable ansatz for <strong>the</strong> bulk solution is<br />

<strong>the</strong>refore<br />

B(q, t>, t, t 1 J∆−2(qt>) + C > �<br />

2 Y∆−2(qt>)<br />

where <strong>the</strong> normalization is fixed by <strong>the</strong> jump condition,<br />

so that<br />

× � C < 1 J∆−2(qt) B(q, t>, t 1 C< 2 − C< 1 C> 2<br />

1<br />

Lt ′<br />

2πrcM 2 KK<br />

(2.70)<br />

, (2.71)<br />

. (2.72)<br />

The rema<strong>in</strong><strong>in</strong>g coefficients are fixed by <strong>the</strong> boundary conditions. We will be ma<strong>in</strong>ly<br />

<strong>in</strong>terested <strong>in</strong> gauge bosons, that is ∆ = 3. However, a mass term may be <strong>in</strong>duced by<br />

a bulk Higgs, and can <strong>the</strong>n be written as<br />

c 2 A → L v2 4g2 4<br />

4M 2 , (2.73)<br />

KK<br />

<strong>in</strong> which we follow [57] <strong>in</strong> def<strong>in</strong><strong>in</strong>g g5 = √ 2πrcg4, and fur<strong>the</strong>r use v4 = ɛv5 √ √<br />

as well as<br />

adjust<strong>in</strong>g <strong>the</strong> mass dimension by 〈H〉 = v5 k/ 2. Note, that this expression is not<br />

general, but true for <strong>the</strong> SM. 9 In <strong>the</strong> case of such a spontaneous symmetry break<strong>in</strong>g<br />

<strong>in</strong> <strong>the</strong> bulk, one also has to <strong>in</strong>troduce <strong>the</strong> correspond<strong>in</strong>g Goldstone bosons ϕA <strong>in</strong> <strong>the</strong><br />

gauge fix<strong>in</strong>g term <strong>in</strong> (2.52),<br />

�<br />

∂µA µ − ξ<br />

r2 ∂φe<br />

c<br />

−2σ �2 �<br />

Aφ → ∂µA µ �<br />

√k v5g5<br />

− ξ<br />

2 ϕA + 1<br />

r2 ∂φe<br />

c<br />

−2σ ��2 Aφ . (2.74)<br />

Note, that <strong>in</strong> this model a l<strong>in</strong>ear comb<strong>in</strong>ation of Aφ and <strong>the</strong> Goldstone boson ϕA,<br />

which has mass dimension [ϕA] = 3/2, is absorbed by <strong>the</strong> KK modes of <strong>the</strong> Aµ, while<br />

<strong>the</strong> o<strong>the</strong>r comb<strong>in</strong>ation rema<strong>in</strong>s physical, see [50, App. A]. As a consequence, <strong>the</strong>re<br />

is a tower of additional pseudo scalars, which is a dist<strong>in</strong>ctive signal of a bulk Higgs<br />

mechanism.<br />

This is not <strong>the</strong> case if brane Higgs fields are <strong>in</strong>troduced, which can be implemented<br />

9 O<strong>the</strong>r gauge groups and symmetry break<strong>in</strong>g patterns <strong>in</strong>duce different numerical factors, compare<br />

Section 3.6.

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