Studies In Higgs Physics And Qcd Resummations

This thesis is mainly centered around specific studies of radiative corrections involving the Higgs boson. We first consider the Stealthy Higgs Model, which assumes that the Higgs boson interacts with a set of scalar particles carrying no Standard Model charge. We explicitly show such possibility is consistent with current experiments. As a consequence, the Higgs signal at the Large Hadron Collider (LHC) is broadened and can be hidden by the large background. The Next Linear Collider (NLC) might then be the facility to observe the Higgs boson. We then discuss some aspects of observing the Higgs boson through the two photon decay mode. We develop a method to resum Sudakov-like large QCD corrections to this process. More specifically, leading logarithms of the type anslog 2nm2 Hm2b and next-to-leading logarithms (NLL) of the type anslog 2n- 1m2 Hm2 b are resummed to all-loop-orders. We find that the NLL contributions account for 5% of that at the leading order, thus indicating that the resummation is under control. The process γγ → bb¯ is the dominant background for Higgs production at a future photon photon collider. Here again, there are similar large logarithms, anslog 2ns m2b and anslog 2n- 1s m2b , which have to be resummed to all orders. We show explicitly that leading logarithms from non-Sudakov-like configurations cancel in subgroups at three-loop order. The corresponding cancellations of next-to-leading logarithms are proven at two-loop order. The mechanism for the cancellations can be readily generalized to all- loops. With this understanding, we can employ a similar approach as for H → γγ to achieve resummation of up to next-to-leading logarithms at all-loop-orders. The NLL contributions are less than 8% of those from leading order, again indicating a stable resummation and ensuring that the radiative corrections are under control. CP violation is also an important issue. The preliminary experimental result on CP asymmetry in the Bd → &phis; KS decay exhibits 2.7σ deviation from the Standard Model prediction. It could be the first evidence for low-energy beyond Standard Model physics if the deviation is finally confirmed. Although its discussion lies somewhat outside the main theme of this thesis, we include it in an appendix due to its importance. We will show the Minimal Supersymmetric Standard Model (MSSM) can easily accommodate the experimental result with certain types of mass insertions in gluino mediated Flavor Changing Neutral Current (FCNC). On the other hand, the Higgs mediated FCNC cannot explain the experimental result