On the Flavor Problem in Strongly Coupled Theories - THEP Mainz

UNIVERSITY OF MAINZ
ABSTRACT
THEORETICAL HIGH ENERGY PHYSICS (THEP)
INSTITUT FÜR PHYSIK
Doctor rerum naturalium
by Martin Bauer
This thesis is on the flavor problem of Randall Sundrum models and their strongly
coupled dual theories. These models are particularly well motivated extensions of the
Standard Model, because they simultaneously address the gauge hierarchy problem
and the hierarchies in the quark masses and mixings. In order to put this into context,
special attention is given to concepts underlying the theories which can explain
the hierarchy problem and the flavor structure of the Standard Model (SM). The
AdS/CFT duality is introduced and its implications for the Randall Sundrum model
with fermions in the bulk and general bulk gauge groups is investigated. It will be
shown that the different terms in the general 5D propagator of a bulk gauge field can
be related to the corresponding diagrams of the strongly coupled dual, which allows
for a deeper understanding of the origin of flavor changing neutral currents generated
by the exchange of the Kaluza Klein excitations of these bulk fields.
In the numerical analysis, different observables which are sensitive to corrections from
the tree-level exchange of these resonances will be presented on the basis of updated
experimental data from the Tevatron and LHC experiments. This includes electroweak
precision observables, namely corrections to the S and T parameters followed by corrections
to the Zb ¯ b vertex, flavor changing observables with flavor changes at one
vertex, viz. B(Bd → µ + µ − ) and B(Bs → µ + µ − ), and two vertices, viz. Sψφ and |ɛK|,
as well as bounds from direct detection experiments.
The analysis will show that all of these bounds can be brought in agreement with a
new physics scale ΛNP in the TeV range, except for the CP violating quantity |ɛK|,
which requires ΛNP = O(10) TeV in the absence of fine-tuning. The numerous modifications
of the Randall Sundrum model in the literature, which try to attenuate this
bound are reviewed and categorized.
Subsequently, a novel solution to this flavor problem, based on an extended color
gauge group in the bulk and its thorough implementation in the RS model, will be
presented, as well as an analysis of the observables mentioned above in the extended
model. This solution is especially motivated from the point of view of the strongly
coupled dual theory and the implications for strongly coupled models of new physics,
which do not possess a holographic dual, are examined.
Finally, the top quark plays a special role in models with a geometric explanation of
flavor hierarchies and the predictions in the Randall-Sundrum model with and without
the proposed extension for the forward-backward asymmetry At FB in top pair
production are computed.