Standard And Covariant Light Front Approaches And Their Application In The Semileptonic Decays Of B-flavor Hadrons

Heavy flavor physics is one of the most important parts of particle physics,especially bflavor hadrons.It plays an indispensable role in accurately testing the standard model of particle physics,finding indirect signs of new physics,and exploring the origin of CP violation.In recent years,the "RD(*)anomaly" in the semileptonic B?D(*)??? decays has attracted much attention,which implys a possible new physical effect.If it is confirmed by more accurate high energy physical experiments in the future,a similar anomaly may also exist in other semileptonic decays of b-flavor hadron.In addition,with the rapid development of high energy physical experiments,the semileptonic b-flavor hadron decays with large branching ratio is expected to be observed in future high energy physical experiments.Therefore,similar to the semileptonic B?D(*)???decays,we study other b-flavor hadron semileptonic decays induced by b?c??? transition.In addition,the form factors are necessary non-perturbative inputs in the theoretical calculation of b-flavor hadron semileptonic decays.In this thesis,we use CLF method to calculate these non perturbative quantities.Finally,we present the main body of the thesis,which is composed of the following parts:In this thesis,firstly,we study the light-front quark models(LFQM)in detail.And then,we investigate the tensor form factors of P?P,S,V,A transitions within the standard light-front(SLF)and the covariant light-front(CLF)quark models(QMs),and self-consistency and Lorentz covariance of SLF QM and CLF QM are analyzed via these quantities.The research found that such two problems have the same origin(the non-vanishing ?-dependent spurious contributions associated with B functions),and can be resolved simultaneously by employing the self consistent scheme(type-? scheme).Besides,we find a "new" self consistence problem of traditional CLF quark model for the first time.It is found that this "new" self consistence problem can also be solved by self consistent type-? scheme.Finally,using the CLF approach with the covariant and self-consistent type-? scheme,the theoretical predictions for the tensor form factors of c?q,s(q=u,d)induced Dq,s?P,S,V,A and b?q,s,c induced Bq,s,c P,S,V,A transitions are presented.Considering that similar to the semileptonic B?D(*)??? decays,the the semileptonic B*?V???(V=Du,d*,Ds*,J/? and ?=e,?,?)and ?(1S,2S)?Bc*??? decays induced by b?c??? transition can further test "RD(*)anomaly",and they are also an ideal process to test the accuracy of form factors which are non-perturbative quantities.Therefore,we study these two types of semileptonic decay in detail.The CLF method is used to calculate the form factors of B*?V and ?(1S,2S)?Bc*transitions respectively.And the results obtained are used to calculate and analyze the semileptonic B*?V??? and ?(1S,2S)?Bc*??? decays respectively.Finally,The theoretical predictions for the observables including the branching ratio,the lepton spin asymmetries and forward-backward asymmetries,branching ratio fractions and so on are presented.Numerically,the B*and ?(nS)semileptonic decays have relatively large branching fractions,which are expected to be observed in future high energy physical experiments.Our results provide a theoretical reference for the change of calculation method of non-perturbative quantities and the detection of b-flavor hadron semileptonic decays in future high energy physical experiments.