Scalar-mediated New Physics In B_s,d??⁺?^-Decays

After the discovery of the Higgs boson,the Standard Model(SM)of particle physics has been proved to be one of the most accurate theory every discovered by human beings.Although it has achieved great success,it is well known that there have been some unsolvable problems,such as the hierachy problem,problem of the tiny neutrino masses.In addition,in order to explain a varity of astrophysical observations,people have to add Dark Matter to the matter components of the universe.However,the SM can not give a reasonable explanation for the structure of Dark Matter.Therefore,the SM is not a perfect theory and needs to be extended.During the same period,huge efforts have been devoted to direct searches for New Physics beyond the SM(NP)at high-energy colliders,e.g.,the coming Run III of the LHC(Large Hadron Collider)and the planned CEPC(Circular Electron-Positron Collider).In this respect,high-energy colliders can directly search for the NP particles predicted by a particular NP model,or one class of NP particles in a model-independent framework.In this thesis,we investigate a scalar NP particle with top-quark FCNC interactions,which belongs to the latter case.B physics has played an important role in the funding of SM,and is considered to be a crucial place to test the SM and serach for NP beyond it.In this paper,we mainly study the effect of a scalar particle S with top quark flavor change neutral flow on the decay process of B_s,d??⁺?^-.In the SM,the leptonic decays B_s,d??⁺?^-is suffered from both the GIM mechanism and the helicity suppression,which result in a branching ratio of order 10-9?-10.Therefore,B_s,d??⁺?^-decays are sensitive to the NP effects.Furthermore,due to the development of multi-loop calculation technologies and the progress of the Lattice QCD,theoretical predictions of the B_s,d??⁺?^-decays become more and more accurate.With the running of LHCb,B_s,d??⁺?^-decays will play an important role in the indirect searches for NP.In this thesis,we consider a NP scalar particle with top FCNC interactions and investigate its effects on the B_s,d??⁺?^-decays.Although the scalar S affect the B_s,d??⁺?^-at one loop level,its effect is not suppresed the CKM factors.In addition,the salar interactions make its effects free of helicity suppression.Therefore,B_s,d??⁺?^-decays is very sensitive to this NP scalar.In this thesis,we calculate the Wilson coefficients of the NP sacalr in the B_s,d??⁺?^-decays and perform detailed numerical analysis.Furthermore,our results are also compared to the sensitivity of this NP scalar at high-energy colliders.The structure and content of this paper are arranged as follows:The 2 chapter introduces the material content of the standard model,the construction of Lagrangian and the Higgs mechanism,and the 3 chapter introduces mixing B_s,d??⁺?^-with neutral B meson system.In chapter 4,we calculate the Wilson coefficient of the scalar S in the B_s,d??⁺?^-decays,and perform detailed numerical analysis.Comparison to the sensitivy at high-energy colliders are also discussed.We draw conclusions and prospects in chapter 5.