Phenomenological Studies Of New Physics Effects In Low-energy Flavour Processes

The Standard Model of particle physics has been successful in describing and predicting a large number of experimental observations,and it has been widely validated spanning various fields by a variety of experiments.Especially,after discovering the Higgs boson in 2012,all the particles in the Standard Model have been discovered experimentally.Although Standard Model has gotten great success in many areas,there are also significant problems in it.Many anomalies have been observed in our universe.There exist several categories of anomalies,including flavour anomalies,multi-lepton anomalies at the LHC,neutrino anomalies,astrophy sical anomalies,cosmological anomalies and anomalies in ultra-high energy cosmic rays.Moreover,gravitational interactions cannot be combined with other fundamental interactions through the Standard Model.But in the current experiments,there is no convincing resonances observed to offer direct guidance to particle physics.But the passion for New Physics has not been diminished.We will search New Physics from the anomaly of flavor physics in the low energy processes.In this thesis,we search for potential new physical effects based on higgs flavour changing neutral current with Higgs coupling to leptons,the anomaly from the CDF W-boson mass,b→sl+ltransition and(g-2)μ.In our first work,we are motivated from the CDF W-boson mass shift.The recently updated measurement of the W-boson mass by the CDF collaboration is about 7σ deviation from the standard model value obtained from the electroweak global fit,which implies that there exists new physics beyond the Standard Model.This observed discrepancy can be explained by new fermions carrying an electroweak gauge charge by affecting the vacuum polarization of the gauge bosons.If a fermion has the same quantum number as the Standard Model quark.They can mix with each other and change the penguin diagram of the b→sl+l-transitions.Thus,the Wboson mass shift may be associated with anomalies in the b→sl+l-transition observed in the LHCb collaboration over the past few years.To explore this possibility,we consider the model containing a vector-like top partner under the new U(1)’symmetry.We find that b→sl+lanomalies and the latest CDF mW shift can be simultaneously accommodated at 2σ level.The second work expands on the first work by introducing a moun-partner to make the model UV complete.Our model can accommodate the(g-2)μ the CDF W-boson mass shift and the b→sl+l-anomalies,while satisfying the other constraints such as the ν trident production and the Zμ+μ-coupling.In the third work,we assume new physic may appear behind Higgs mechanism,then offdiagonal element of Yukawa matrix of charge lepton can exist,which contribute to process such as μ→eγ,μ→3e,μ→e conversion,τ→eγ,τ→μγ and others in low energy experiment and h→eτ,h→μτ in high energy experiment.We calculate tree level,one-loop and twoloops effect to these effects in full theory and get wilson coefficient in analysis form.After matching them to a complete basis of low energy effective operator,we translate electroweak scale via one-loop QCD and one-loop QED renormalization group equations to experimential scale,considering threshold effect,mixing of scalar,tensor and dipole and get the constrains on off-diagonal element of Yukawa matrix.Yukawa coupling at electroweak scale.We also give uncertain of the constraint due to uncertain of quark-currents in the nucleus.In the end,we summarize and outlook,and add some details of the article in the appendix.