Studies Of B-meson Mixings And Decays Within Supersymmetry Models

The Standard Model(SM),the most successful particle physics theory describing electromagnetic,weak and strong interactions,has been verified by almost all the experiments since its establishment.However,there are still some unknown questions in the Standard Model,such as the fine-tuning problem of the Higgs mass,the inability to provide dark matter candidates,not being able to explain the experimental anomalies like RK and so on.Therefore,we need to explore the New Physics(NP)beyond the Standard Model.Although the high energy physics experiments can directly detect new physics particles,it is also necessary to investigate the effects of these hypothesized new physics particles on the low-energy processes.In this dissertation,we shall study the new physics effects on B-meson mixings and decays.The new physics models involved are the Next-to-Minimal Supersymmetric Standard Model(NMSSM)and the R-Parity Violating(RPV)Minimal Supersymmetric Standard Model(MSSM).We begin with the phenomenological study of B3(d)-meson mixings and decays in the NMSSM.Motivated by the observation that the Standard Model predictions are now above the experimental data for the mass difference ?Ms(d),we perform a detailed study of Bs(d)-Bs(d)mixing and Bs??+?-decay in the Z3-invariant NMSSM with non-minimal flavour violation,using the recently developed procedure based on the Flavour Expansion Theorem(FET),with which one can perform a purely algebraic mass-insertion(MI)expansion of an amplitude written in the mass eigenstate basis without performing any diagrammatic calculations in the interaction/flavour basis.Specifically,we consider the finite orders of mass insertions for neutralinos but the general orders for squarks and charginos,under two sets of assumptions for the squark flavour structures.By checking if the Flavour Expansion Theorem results agree with the ones calculated directly in the mass basis,our estimation for the optimal cutting-off mass insertion orders has been examined.Our analytic results are then expressed directly in terms of the initial Lagrangian parameters in the interaction/flavour basis,making it easy to impose the experimental bounds on them.It is found numerically that the NMSSM effects with the above two assumptions for the squark flavour structures can accommodate the observed deviation for ?Ms(d),while complying with the experimental constraints from the branching ratios of Bs??+?-and B??Xs? decays.In the second part of this dissertation,we perform a complete one-loop calculation of the b?s?+?-Wilson coefficients in the R-Parity Violating MSSM.Recently,the updated measurements of RK indicate that the Lepton-Flavour Universality(LFU)anomaly still exists.We use the model-independent global fit containing both the Lepton-Flavour Universality operators and the Lepton-Flavour Universality Violating(LFUV)operators.We found that the photon penguin diagrams in R-Parity Violating MSSM can provide the Lepton-Flavour Universality Wilson coefficient in the specific parameter space.In this fit-scenario,we assume that the masses of the second and third generations of sneutrino have a large split,then the b?sl+l-and RD(*)anomaly can be explained simultaneously at 2? level while complying with the experimental constraints from Bs-Bs mixing,B?K(*)?? and Z decays to two charged leptons and so on.In the future with the experimental progress in direct searches for supersymmetric particles as well as the more and more precise nonperturbative calculations from like Lattice,the supersymmetric effects on these low-energy flavour processes could be further examined.