Single t-Quark Productions via Flavor-Changing Processes in Topcolor-Assisted Technicolor Model at Hadron Colliders

In the framework of topcolor-assisted technicolor （TC2） model, there exist tree-level flavor-changing （FC） couplings, which can result in the loop-level FC coupling tcg. Such tcg coupling can contribute significant clues at the forthcoming Large Hadron Collider （LHC） experiments. In this paper, based on the TC2 model, we study some single t-quark production processes involving tcg coupling at the Tevatron and LHC： pp（pp） → tq （q = u, d, s）, tg. We calculate the cross sections of these processes. The results show that the cross sections at the Tevatron are too small to observe the signal, but at the LHC it can reach a few pb. With the high luminosity, the LHC has considerable capability to find the single t-quark signal produced via some FC processes involving coupling tcg. On the other hand, these processes can also provide some valuable information of the coupling tcg with detailed study of the processes and furthermore provide the reliable evidence to test the TC2 model

Searching for Flavor-Changing Neutral-Current Signals via e^+e^-(γγ)→th_t^0 in Topcolor-Assisted Technicolor Model

In the context of the top-color-assisted technicolor （TC2） model, the flavor-changing neutral-current （FCNC） interaction induced by the top-higgs （hOt） are predicted at tree level. We study the relevant processes of e＋e-（γγ）→tcht0 at the International Linear Collider （ILC）. It is found that these rare processes production rates can be enhanced significantly in the TC2 model. Especially for the process γγ→tcht0, the total cross section will reach a few fb in the reasonable parameter space. We also calculate the distributions of transverse momenta, pseudo-rapid and invariant mass of the top-higgs. In view of the main decay modes of top-higgs for mho 〈 2mr, we find that there will be several hundreds FCNC events produced at the ILC with annually integral luminosity of 500 fb-1. Due to the clean background, such FCNC signals can possibly be detected at the ILC.

Flavor-Changing Bottom-Strange Associated in the Littlest Higgs Model with T-parity at the ILC

In the littlest Higgs model with T-parity(LHT) the mirror quarks induce the special flavor structures and some new flavor-changing couplings,which could greatly enhance the production rates of the flavor-changing processes. We in this paper study some bottom and anti-strange production processes in the LHT model at the International Linear Collider(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.

Probing the top quark flavor-changing couplings at CEPC

We propose to study the flavor properties of the top quark at the future Circular Electron Positron Collider(CEPC) in China.We systematically consider the full set of 56 real parameters that characterize the flavor-changing neutral interactions of the top quark,which can be tested at CEPC in the single top production channel.Compared with the current bounds from the LEP2 data and the projected limits at the high-luminosity LHC,we find that CEPC could improve the limits of the four-fermion flavor-changing coefficients by one to two orders of magnitude,and would also provide similar sensitivity for the two-fermion flavor-changing coefficients.Overall,CEPC could explore a large fraction of currently allowed parameter space that will not be covered by the LHC upgrade.We show that the c-jet tagging capacity at CEPC could further improve its sensitivity to top-charm flavor-changing couplings.If a signal is observed,the kinematic distribution as well as the c-jet tagging could be exploited to pinpoint the various flavor-changing couplings,providing valuable information about the flavor properties of the top quark.