##### Abstract

This thesis sets out to explore the methods of and the space available when adding new quarks to

the particle content of the Standard Model and the Left-Right Symmetric Model (LRSM).

Most observations of interactions mediated by the electromagnetic, weak and strong forces can be

adequately explained by the Standard Model. It is known, however, that the Standard Model must

be the effective theory of an extended model which is possibly broken down at a higher energy

scale. The rare deviations of measurements from the Standard Model predictions make it difficult

to grasp and constrain new physics. There are also a number of models which suffer under a

large number of parameters and therefore reveal a difficulty which occurs during model-building,

namely that there exists a fine line between a model which can predict the outcome of an experiment

after inserting a reasonable number of parameters and a model which loses its predictive

capability since the large number of parameters can be arranged in such a way that almost every

possible outcome can be produced.

There is thus a wide range of models based on similar principles to the Standard Model which

have been proposed as possible extensions, including Spontaneous Symmetry Breaking, an extended

Higgs sector and an extended gauge symmetry at a higher energy scale. This thesis lists

and describes some representatives of those models, specifically the Left-Right Symmetric Model,

the Little Higgs Model and the Standard Model with an extended quark sector.

Methods of introducing new quarks to a Lagrangian and the quarks’ mass-gaining process are discussed

in detail. Subsequently the Left-Right Symmetric Model is extended by a vector-like quark

isosinglet and it is shown that in effect, a model extended by an additional Top-quark receives two

additional parameters, the Top-quark mass and the mixing angle theta, as well as a quark mass sign

for every quark.

Parameters of the LRSM with and without an additional heavy quark involved in the calculations

of the B_d-meson mass-mixing, the CP-violating parameter epsilon_K and the B_s-meson decay to two

muons are constrained when calculating those quantities including one-loop corrections.

It emerges that the B-meson mass-mixing and the CP-violating parameter only leave space for an

LRS extension or an additional Top-quark if one allows the Standard Model parameters to alter.

Thus lower bounds, depending on the uncertainty of the Standard Model input parameters, of the

right-handed W-mass are derived and compared with bounds derived in the literature.

It is found that considering both the LRSM and an additional heavy quark leaves space for the new

particles even without altering the Standard Model parameters, due to cancellations between the

two new contributions. Therefore fixing the right-handed W-mass gives a an upper bound to the

Top-mass.

The mixing angle theta is constrained by using the decoupling theorem.

When analysing the CP-violating parameter in the LRSM extended by a Top-quark two regions of

quark mass sign choices are found as well as a constraint on the phase of the vacuum expectation

value arising in the Higgs sector of the LRSM.

In discussing the Bs-meson decay to two muons, the problem of imprecise hadron matrix elements

and the model-dependent interpretation of measured CKM matrix element values is solved by

introducing the new physics-measuring quantity A_s. It is shown that the branching ratio of the

Bs-decay in the LRSM is enhanced for all choices of new parameters and all mass signs set to plus

one. Thus measuring the branching ratio could distinguish between the LRSM and the Standard

Model. The enhancement becomes larger the smaller the W_R-mass and thus once the branching

ratio is observed, a lower bound on the right-handed W-mass can be derived.

A qualitative discussion on the ways in which to extend the calculation of the B_s-meson decay

branching ratio in order to describe an additional Top-quark is made. It is concluded that an enhancement

of A_s is possible.