On the Flavor Problem in Strongly Coupled Theories - THEP Mainz

A t FB ���
8.75
8.70
8.65
8.60
2 4 6 8 10
MKK �TeV�
4.5. Numerical Analysis 169
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Figure 4.8: The forward backward asymmetry At FB in the minimal RS model plotted
for the complete dataset versus MKK. The red line indicates the SM value.
asymmetry as envisioned. Given that ˜ CV uū > 0 is a robust prediction of the RS framework,
as long as the top quark is mainly composite, we conclude that the corrections
to At FB are necessarily negative.
This feature is illustrated in Figure 4.8, which shows the predictions for the RS corrections
to the forward-backward asymmetry for our complete dataset, plotted versus
the KK scale. The central value of the SM prediction is indicated by the red line.
It is evident, that the maximal attainable effects amount to not even −0.05%. For
all parameter points, the correction to the total inclusive cross section is larger than
the contribution to the asymmetric cross section, which fixes the sign of the overall
correction. Another representation of the small effects can be found in Figure 4.10,
which shows that the scatter plot of the complete parameter set in the � C V uū− � C A uū plane
ends up in the tiny red region. These results should be contrasted with the analysis
[124], which finds positive corrections to the t¯t forward-backward asymmetry of up to
5.6% (7%) arising from KK gluons (Z ′ -boson exchange) at LO. In the latter article,
sizable corrections to ˜ C A q¯q arise since the 5D doublet and singlet light-quark fields are
localized at different ends of the extra dimension by choosing cuL = cdL ∈ [−0.4, 0.4]
(IR-localized) and cuR = cdR = −0.8 (UV-localized).10 This will sabotage the generation
of hierarchical masses and mixings on the basis of fundamental anarchic parameters.
As a consequence, one would have to reintroduce a structure in the fundamental
Yukawas in order to make such a model viable.
10 Notice that the convention of the bulk mass parameters used in [124] differs from ours by an
overall sign.