The Study On The Neutral Meson Mixing In Supersymmetry Model With Local Gauged Baryon And Lepton

We perform an analysis on B0-B0mixing in the extension of the minimal supersymmet-ric standard model where baryon and lepton numbers are local gauge symmetries (BLMSSM) by using the effective Hamiltonian method. And the constraint of a125GeV Higgs to the parameter space has also been considered. The numerical results indicate that the contri-butions of the extra particles can be sizeable in B0-B0mixing. For certain parameter sets, the theoretical prediction of mass differences ΔmB agrees with the current experimen-tal result. Furthermore, B0-B0mixing in the BLMSSM can preliminarily constrain the parameter space. We also analyze the CP asymmetry aisd for the B0-B0in the BLMSSM. And the numerical results indicate that the theoretical prediction of afsd agrees with the cur-rent experimental result. For certain parameter sets, the value of afsd can be sizable. With the development of more precise theoretical analysis and experimental determinations, the B0-B0mixing in the BLMSSM will have a clearer picture and the parameter space in this model will also be further constrained.The thesis includes six chapters, and our research works contained in the chapters from3to5.In Chapter1, the Standard Model (SM) of particles physics is introduced, including the main ideas and the history of this model, the content of the particles, the lagrangian and the Higgs mechanism.Chapter2, we give a short introduction to the Minimal Supersymmetry Standard Model (MSSM), including the content of the particles, the lagrangian with the superpotential and the soft breaking terms, R-parity and the mass of Higgs.Chapter3introduces main features of the BLMSSM. First we introduce the background of this model, then, the superfields, the superpotential as well as the soft breaking terms are introduced, after the Higgs fields acquire the Vacuum Expectation Values (VEVs), the local gauge symmetry SU(2)L<g> U(1)Y(?) U(1)B(?)U(1)L is broken down to the electro-magnetic symmetry U(1)e. After that, we obtain the physics spectrum and couplings needed for the calculation of B0-B0mixing. In particular, the constraint of a125GeV Higgs is discussed.Chapter4first outlines the basic formulae and research method for the calculation of B0-B0mixing. Then, the Wilson coefficients are computed and the local operators with color non-singlet are rearranged by the Fierz rearrangement. Considering the QCD corrections the anomalous-dimension matrix is given, finally, using the renormalization group equation, we obtain the mass difference ΔmB at the hadron scale. Ending with the discussion of the numerical analysis. We find the contributions of the extra particles can be sizeable in B0-B0mixing. For certain parameter sets, the theoretical prediction of mass differences ΔmB agrees with the current experimental result. Furthermore, B0-B0mixing can preliminarily constrain the BLMSSM parameter space.In chapter5, we first introduce the CP sources and CKM in SM, then, we discuss the CP sources in BLMSSM, the analytical expressions of the CP asymmetry afsd for the Bd-Bd mixing are obtained. The numerical results indicate that the theoretical prediction of afsd agrees with the current experimental result. For certain parameter sets, the BLMSSM contributions can be sizable in CP asymmetry for the Bd-Bd mixing, which may help understand questions of in cosmology.Chapter6summarises our results, the conclusions and suggestions for future research work are given.