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On the Flavor Problem in Strongly Coupled Theories - THEP Mainz

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(ND)<br />

and all possible<br />

Higgs<br />

<strong>in</strong>sertions<br />

2.3. Profiles of Gauge Bosons 63<br />

This is <strong>the</strong> “messiest” scenario, <strong>in</strong> <strong>the</strong> sense that all possible diagrams <strong>in</strong><br />

Figure 2.7 contribute to <strong>the</strong> propagator, besides <strong>the</strong> pure gauge boson<br />

propagator, because it will be massive due to mix<strong>in</strong>g with a composite<br />

which breaks <strong>the</strong> gauge symmetry. In <strong>the</strong> language of Section 2.2, <strong>the</strong><br />

group I is empty here. The correspond<strong>in</strong>g propagator should have flavordiagonal,<br />

∆F = 1 and additional ∆F = 2 contributions and we f<strong>in</strong>d<br />

D ξ=1<br />

µν (q, t; t ′ ) = ηµν L<br />

4πrc M 2 KK<br />

� t 2 < − t 2 − t ′2 + 1 � . (2.87)<br />

This is not exactly what one would expect. The Higgs corrections to<br />

<strong>the</strong> ∆F = 2 contributions we found for (DD) BCs are absent. This can<br />

not be expla<strong>in</strong>ed by a direct cancellation between diagrams, because<br />

all o<strong>the</strong>r diagrams will not lead to ∆F = 2 effects. Also, <strong>the</strong> flavordiagonal<br />

factor is much larger compared to (NN) BCs, which can only<br />

be expla<strong>in</strong>ed by <strong>the</strong> Higgs <strong>in</strong>sertions <strong>the</strong>re hav<strong>in</strong>g a large effect.<br />

We will close this section with <strong>the</strong> <strong>in</strong>troduction of <strong>the</strong> KK decomposition for <strong>the</strong><br />

different scenarios just <strong>in</strong>troduced and a discussion of <strong>the</strong> behavior of <strong>the</strong> profile<br />

functions for <strong>the</strong> lightest modes.<br />

The generic bulk Lagrangian (2.53) suggests a KK decomposition <strong>in</strong> t-notation<br />

� �<br />

Aµ(xµ, t)<br />

=<br />

A5(xµ, t)<br />

1<br />

�<br />

� An µ(xµ) χn(t)<br />

√<br />

rc<br />

�<br />

. (2.88)<br />

n<br />

MKK A n 5 (xµ) ∂tχn(t)<br />

If this decomposition is <strong>in</strong>serted <strong>in</strong>to equation (2.53), one f<strong>in</strong>ds <strong>the</strong> important relation<br />

(valid <strong>in</strong> Feynman gauge)<br />

iDµν(q, t; t ′ ) =<br />

∞�<br />

n=0<br />

−iηµν<br />

q 2 − x 2 n + iɛ χn(t)χn(t ′ ) , (2.89)<br />

<strong>in</strong> which xn ≡ mn/MKK and mn denotes <strong>the</strong> mass of <strong>the</strong> nth KK mode. This shows<br />

how <strong>the</strong> 5D propagator is equivalent to <strong>the</strong> exchange of <strong>the</strong> whole KK tower and<br />

represents ano<strong>the</strong>r connection to <strong>the</strong> strongly coupled dual <strong>the</strong>ory, compare (2.42). It<br />

also follows that <strong>the</strong> normalization of <strong>the</strong> k<strong>in</strong>etic terms imposes <strong>the</strong> orthonormality<br />

relation<br />

2π<br />

L<br />

� 1<br />

ɛ<br />

dt<br />

t χm(t)χn(t) = δmn . (2.90)<br />

Fur<strong>the</strong>r, all terms <strong>in</strong>clud<strong>in</strong>g derivatives with respect to φ and <strong>the</strong> bulk mass have to<br />

be matched to a 4D mass term for each mode. The result<strong>in</strong>g equations are called<br />

EOM, and read for <strong>the</strong> vector component<br />

�<br />

1<br />

− t∂t<br />

t ∂t + c2 A<br />

t2 �<br />

χn(t) = x 2 nχn(t) . (2.91)

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