Study Of ?_b??_c?(?)_? Decay In The Standard Model And The Aligned Two-Higgs-Doublet Model

The averages of R(D*)and R(D)measurements,evaluated by the Heavy Flavor Averaging Group,exceed the Standard Model predictions by 3.4a and 2.3? respec-tively,which implies possible presence of New Physics beyond the Standard Model.At the quark level,both B?D(*)?-v? and Ab?Ac?-v? decays are induced by the same b ? c?v? transition.Though the decay Ab?Act-v? has not been measured experimentally,we can study the New Physics effect on this decay,using the com-bined constraints on the corresponding New Physics parameters from the R(D*)and R(D)data.This is the main content of this thesis.We firstly discuss the difference between the form factors obtained by the QCD sum rules and the ones obtained by the lattice QCD approaches.Then,using these two kinds of form factors,we cal-culate the differential decay width,the branching ratio and the forward-backward asymmetry of Ab?Ac?-v? decay in a model-independent New Physics framework.After that,we study in detail the impact of the aligned Two-Higgs-Doublet Model on the decay Ab?Ac?-v?.Using the information of B,D,and Ds leptonic decays to constrain the coupling parameters of the A2HDM,we get the following four sets of solutions:?sl*sd/MH2±?[-0.036,0.008]GeV-2,sl*su/MH2±?[-0.006,0.037]GeV-2;?sl*sd/MH2±?[-0.036,0.008]GeV-2,sl*su/MH2±?[0.511,0.535]GeV-2;?sl*sd/MH2±?[0.064,0.108]GeV-2,sl*sd/MH2±?[-0.006,0.037]GeV-2;?sl*sd/MH2±?[0.064,0.108]GeV-2,sl*sd/MH2±?[0.511,0.535]GeV-2.Then,we investigate the effect of these four set of parameters on the decay Ab?Ac?-v?.We find that the results obtained with the third set of coupling parameter-s are much larger than the Standard Model predictions,while the results obtained with the fourth set of coupling parameters are smaller than the Standard Model pre-dictions.Combining further the constraints from RDRatio and RDRatio,we then find that the latter three cases are already excluded.For the first set,sl*su/MH2±?[-0.036,0.008]GeV-2,sl*su/MH2±?[-0.006,0.037]GeV-2,the New Physics has on-ly little effect on the decay width,the branching ratio,and the forward-backward asymmetry of Ab?Ac?-v? decay.These results will be helpful for our further understanding of the possible New Physics current structures involved in b?c?v?decays.