Phenomenological Study Of The New Physics Models At High Energy Colliders Via Some Processes

In spite of the remarkable success of the Standard Model (SM) in unraveling the basic laws of nature at the smallest accessible length scale and describing all the existing experimen-tal data, the elusive Higgs boson, which is responsible for the electroweak symmetry breaking (EWSB) mechanism in the SM, is yet-to-be found experimentally. However, many theoretical arguments and experimental observations indicate that the model is incomplete and that it should be embedded in a more fundamental theory. One of the major motivations for physics beyond the SM is to resolve the hierarchy and fine-tuning problems between the electroweak scale and the Planck scale. Technicolor theory, which is a kind of dynamical EWSB theory, introduce new strong dynamics at scales not much above the electroweak scale, thus defer the hierarchy problem. The Littlest Higgs model, which is based on a non-linearσmodel describ-ing an SU(5)/SO(5) symmetry breaking, solves the problems by eliminating the lowest order contributions via the presence of a partially broken global symmetry.Among various kinds of dynamical EWSB models, the topcolor-assisted technicolor (TC2) model is especially attractive since it connects the top quark with the EWSB. In this model, the topcolor interactions make small contributions to the EWSB, but give rise to the main part of the top quark mass(1-ε)mt with a model dependent parameterε. The technicolor interactions play a main role in the EWSB, and the extended technicolor (ETC) interactions generate masses of lighter fermions and give contributionεmt to the full mt. This model predicts the existence of three CP-odd pseudo Goldstone bosons (PGB’s) called top-pions(πt±,πt0) and a CP-even salar (ht0) called the top-Higgs, which are condensates of the third generation quarks and have strong couplings with the third generation quarks. The existence of these new particles can be regarded as a typical feature of the TC2 model. Another feature of the TC2 model is the existence of large flavor-changing couplings. In TC2 models the topcolor interactions are non-universal and therefore do not posses a Glashow-Illiopoulos-Maiani (GIM) mechanism. This non-universal gauge interactions result in some flavor-changing-neutral-current vertices when one writes the interactions in the quark mass eigenbasis.In the Littlest Higgs model in addition to the SM particles, new charged heavy vector bosons (WH±), a neutral heavy vector boson (ZH0),a heavy photon(AH), a heavy top quark (T+) and a triplet of scalar heavy particles (Φ) are present. A consistent and phenomenologically viable Littlest Higgs model with T-parity (LHT) requires the introduction of three doublets of "mirror quarks" and three doublets of "mirror leptons" which are odd under T-parity. In the LHT model all new particles listed above, except (T+), are odd under T-parity. Moreover, there is an additional T-odd heavy quark (T-). In LHT model the mirror quarks and mirror leptons could induce the special flavor structures and some new flavor-changing couplings which could greatly enhance the production rates of the flavor-changing processes.Basing on the running large hadron collider (LHC) and the planning international linear collider (ILC), we analyse the conceivable effects of new particles in the TC2 and LHT models to some processes, which include the following aspects:(1) Within the context of TC2 model we investigate the associated production of the neutral top-higgs ht0 with a pair of top quarks i.e. pp→ttht0 at the LHC, which proceeds through the partonic processes qq→ttht0 and gg→ttht0. We present the impact of the top-Higgs mass mht and model dependent parameterεto production cross section of this process, respectively. Our numberical results show that the cross section of pp→ttht0 can reach a few hundreds fb in the most part of the allowed parameter space and even a few tens pb for the light top-Higgs. We also describe the distributions of the transverse momenta of ht0 and investigate the dependence of the tree level cross sections on the renormalization/factorization scale.(2) In the TC2 model we calculate the production cross section of e+e-→ttht0. The results show that the total cross section is typically of the order of 1.0-7.5 fb in the energy range between 1 TeV and 2 TeV of the ILC for the whole top-Higgs mass region of interest. We also present the distributions of the transverse momenta of top-Higgs and top quark, respectively.(3) In the LHT model we study bottom-strange associated production at the ILC, i.e., e+e-→bs andγγ→bs. The results show that the production rates of these processes are sizeable for the favorable values of the parameters. Therefore, it is quite possible to test the LHT model or make some constraints on the relevant parameters of the LHT through the detection of these processes at the ILC.