İNŞaat mühendiSLİĞİ anabiLİm dali

Investıgatıon Of The Hadronıc Fcnc Transıtıons In Unıversal Extra Dımensıon And Some Other New Physıcs Scenarıos
The standard model is recognized as a highly successful theory due to the fact that it has shown the most impressive harmony between the obtained experimental data and theoretical predictions until now. This model has considered to be complete with the discovery of the Higgs boson at the LHC in 2012. Although this theory has been clarified many questions, there are some important conceptual deficiencies such as origin of the matter, gauge and fermion mass hierarchy, matter-antimatter asymmetry, unification, etc. that this model can not answer. In order to solve these problems, many new physics scenarios have been proposed in energies beyond TeV scale. It is believed that the standard model is a low energy manifestations of those more fundamental theories.

The main purpose of this thesis is to analyze some baryonic FCNC transitions like () and using some new physics models such as universal extra dimension with one or two extra dimensions, different supersymmetric models (SUSY I, SUSY II, SUSY III ve SUSY SO(10)) and topcolor-assisted technicolor scenario. The FCNC transitions are important not only for determination of many parameters of the standard model, but also because of their sensitivity to new particles predicted by new physics scenarios. The above mentioned channels are also investigated in standard model. The obtained results from new physics models are compared with the predictions of the standard model.

Firstly, using the form factors calculated via light cone QCD sum rules in full theory, the baryonic FCNC transition is analyzed both in standard model and universal extra dimension scenario in the presence of a single extra compact dimension. Various physical quantities related to this decay channel like branching ratio, forward-backward asymmetry, baryon polarizations and double lepton polarization asymmetries have been calculated and the results obtained in universal extra dimension have been compared with those of the standard model. A lower limit on the compactification scale (1/R) of extra dimension has also been put via comparison of our theoretical results with the experimental data in the baryonic decay channel provided by CDF Collaboration.

In the next part of the thesis, the radiative transition is investigated in the standard model as well as models with one or two compact universal extra dimensions. Using the form factors entered the low energy matrix elements, calculated via light cone QCD, the total decay width and branching ratio of this decay channel are calculated. The results of the extra dimensional models are compared with those of the standard model on the considered physical quantities. It is looked for the deviations of the results from the standard model predictions at different values of the compactification factor.

The next study is the investigation of the semileptonic decay channel in standard model as well as different supersymmetric models. Especially, considering the parametrization of the matrix elements entered the low energy effective Hamiltonian in terms of form factors, the amplitude and differential decay rate responsible for this transition are calculated in supersymmetric models. The form factors calculated via light cone QCD sum rules are again used to analyze the differential branching ratio and lepton forward-backward asymmetry in different supersymmetric models such as SUSY I, SUSY II, SUSY III ve SUSY SO(10). The obtained results are compared with those of the standard model. It is discussed how the results of different supersymmetric models deviate from the standard model predictions.

Finally, the FCNC transition has been comparatively analyzed in the standard model as well as the topcolor-assisted technicolor scenario. The decay width, branching ratio and lepton forward-backward asymmetry related to this decay channel are calculated in those models. The results of the topcolor-assisted technicolor model have also been compared with those of the standard model and it is debated how the results of the topcolor-assisted technicolor model depart from the standard model predictions.

Any comparision of the results obtained in this thesis with the future experimental data on the considered decay channels can help us in the course of search for new physics effects beyond the standard model.