Mixing And Rare Decays Of B Meson And New Physics Corrections

In the framework of the Standard Model (SM) and the Top-quark two-Higgs-doublet model (T2HDM), we made a systematic study of the radiative decay B→X_sγ, semi-leptonic decay B→X_sl⁺l^-, B→K^*l⁺l^-, and B⁰- (B|-)⁰ mixing. By comparing the theoretical predictions and the experimental data, we can impose some constraints on the parameter space of the T2HDM. Within the considered parameter space, we calculated and analyzed the new physics contributions to the effective Wilson coefficients and the physical observables, and found some interesting results.In first two chapters, we provided a brief review about the historic developments and the theoretical frameworks of the B physics, including the low energy effective Hamiltonian, the effective Wilson coefficients and the renormalization group equation (RGE). We calculated and show all formulas needed in the calculation. In chapter 3, we gave a brief introduction for the general two-Higgs-doublet models.In chapter 4, we calculated the new one-loop diagrams contributions induced by the neutral and charged-Higgs bosons to the Wilson coefficients in T2HDM, extracted out the new physics contributions and combined these new physics contributions with their SM counterparts. We then calculated the new physics corrections to the effective Wilson coefficients and relevant physical observables, or drew bounds on the parameter space of the model considered here. According to our calculations and phenomenological analysis, we found the following points:By comparing the theoretical predictions with the data of the decay B→X_sγ, a light charged Higgs boson with a mass less than 200 GeV is excluded. For fixed tanβ= 30 andδ= 0°, the lower limit on m_H⁺ is m_H+≥300 GeV. The data of B→X_sγ also prefer a small angleδ:δ< 44°for tanβ= 30 and m^H+ = 400 GeV.Using the well measuredΔM_d and the first observation ofΔM_s, we found that for fixed m_H⁺ = 400 GeV andδ= [0°,60°], the upper bound on tanβis tanβ≤30 after the inclusion of major theoretical uncertainty. For a small tanβ, say tanβ≤20, a light charged Higgs boson with a mass around 300 GeV is allowed. The bounds on tanβand m_H⁺ are indeed strongly correlated.After the inclusion of new physics contributions, the effective Wilson coefficients C_i^eff(m_b) (i = 7γ, 9V and 10A), which govern the branching ratio of B→X_sl⁺l^-decay, are always SM-like within the considered parameter space of T2HDM. The sign of the interference term remains unchanged. The neutral Higgs bosons contributions to C_Qi(i = 1,2) are negligible small for l = e and remarkable for l =μ, (?).The new physics contributions to C_7γ^eff and C_9V^eff can be significant in magnitude respectively for large tanβ, largeδand lighter charged-Higgs boson, but their contributions to Br(B→X_sl⁺l^-) tend to cancel each other.The neutral Higgs contributions to the branching ratio Br(B→X_sl⁺l^-) interfere constructively with their SM counterparts, but small in magnitude. The charged Higgs, however, can provide larger new physics contributions to B→X_sl⁺l^- than that of neutral Higgs.The branching ratios of decays B→K^*l⁺l^- (l = e,μ) can provide additional constraints in some parts of the T2HDM space. After the inclusion of new physics contributions, the theoretical prediction of differential branching ratio for B→K^*l⁺l^-(l =(?)) deviate greatly from SM.The change of the position of the zero-point of the FBA in B→K^*l⁺l^- in the T2HDM is not sizable. The effects of neutral Higgs bosons could be observed possibly in the FBAs and the lepton polarization especially through decays B→K^*l⁺l^-(l = (?)).In the last chapter, we gave a short summary of this paper and some remarks on future developments of B physics in forthcoming years.