İNŞaat mühendiSLİĞİ anabiLİm dali

Phenomenology Of The Hadronıc Fcnc Transıtıons In Dıfferent Supersymmetrıc Models And Some Other New Physıcs Approaches
The standard model of particle physics has been a successful theory for many years. It has shown a perfect agreement with the experimental data so far and has explained almost all known data. In recent years, significant progresses have been made regarding the investigation of Higgs boson as a missing element of the standard model since 1964. In 2012, the ATLAS and CMS experiments at CERN reported their observations of a Higgs like boson with a mass of 126 GeV at a statistical significance of 5_. Experimental attempts on the decay properties of this boson are continued. Although the standard model has successfully explained almost all data obtained from particle accelerators in a period of nearly twenty years, it can not be considered as a ultimate theory of nature due to many questions that can not be answered by this model. For this reason, some alternative theories under new physics have been proposed. The new physics models have been mainly proposed in energies beyond the TeV scale and it is believed that the standard model is a low energy manifestation of those theories. There are two ways of searches for new physics effects: direct and indirect. In direct search, people are looking for the particles beyond the standard model at colliders directly, but in indirect search, we look at the effects of new particles to the flavor changing neutral current (FCNC) based decay channels. In this connection, in this thesis, some FCNC based channels are studied using some new physics scenarios like different supersymmetric models, extra dimensional models with one or two universal extra dimensions and topcolor-assisted technicolor model. The results obtained are compared with those of the standard model.
As the first study which constitutes the most important part of the thesis, the semileptonic _ transition is studied in standard as well as different supersymmetric models (SUSY I, SUSY II, SUSY III, SUSY SO(10)). In particular, 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 decay channel are calculated in supersymmetric models. The form factors calculated via light cone QCD sum rules in full theory are used to analyze the differential branching ratio and lepton forward-backward asymmetry related to this decay channel in different supersymmetric models. The obtained results are compared with those of the standard model. Also it is discussed how the results of different supersymmetric models deviate from the standard model predictions and which SUSY scenarios are favored.
As the second work, using transition form factors calculated again via light cone QCD sum rules in full theory, the rare radiative _ decay is comparatively analyzed in the standard model and models with one or two universal extra dimensions. The total decay width and branching ratio associated with this decay channel are estimated in extra dimensional models. The obtained results are compared with those of the standard model. It is discussed how the results of universal extra dimensional models approach to the standard model predictions when the compactification factor of extra dimension is increased.
Finally, the flavor changing neutral current process of the _ is comparatively analyzed in the standard model as well as topcolor-assisted technicolor model using the form factors calculated via light cone QCD sum rules in full theory. In particular, the decay width, branching ratio and lepton forward-backward asymmetry related to this decay channel are calculated. The results of the topcolor-assisted technicolor model are compared with those of the standard model and debated how the results of the topcolor-assisted technicolor model depart from the standard model predictions. Also our results on the branching ratio and differential branching ratio are compared with recent experimental data provided by CDF and LHCb Collaborations.
Since the flavor changing neutral current based transitions in baryonic sector provide the most sensitive test for the standard model and are sensitive to new physics effects beyond the standard model, the decay channels considered in this thesis can help us not only in analyzing the experimental data but also in getting useful information about the perturbative and non-perturbative aspects of the quantum chromodynamics.