Lu Gong-Ru

Flavor-changing neutral-current production of t anti-c in association with a neutral top-Higgs at LHC in the topcolor-assisted technicolor model

In the framework of the topcolor-assisted technicolor (TC2) model we investigate the flavor-changing neutral-current production pp → th0t at the Large Hadron Collider (LHC), which proceeds through the parton-level processes gg → th0t, uū → th0t and dd → th0t. We calculate the production rate and present the distributions of the transverse momenta and the invarient mass of the neutral top-higgs. It is found that the cross section of pp → th0t can reach a few hundreds of fb in a large part of the allowed parameter space. Considering the main decay mode of top-higgs for mht < 2mt, we find that such a production may provide copious events. In the case of unobservation, the LHC can set meaningful constraints on the TC2 model.

Detecting Toppion via a Flavor-Changing Single Top QuarkProduction Process*

In the framework of topcolor-assisted technicolor (TC2) theory, we study a flavor changing single top quarkproduction process pp(pp) →Ⅱ0t → tc(tc) at upgraded Tevatron and LHC. The results show that with the flavor changingcoupling of neutral toppion to top and charm quark, toppion provides a large te-channel resonance effect. The signal ofsingle top production could be detected at LHC. Otherwise, the narrow peak in the invariant mass distribution could beclearly detected both at upgraded Tevatron and LHC. Therefore, such single top production process provides a uniqueway to test TC2 model via the detection of tc-channel neutral toppion contribution.

Top quark pair production at e(+)e(-) colliders in the topcolor-assisted technicolor model

In the framework of topcolor-assisted technicolor model we calculate the contributions from the pseudo Goldstone bosons and new gauge bosons to c(+)c(-) --> t (t) over bar. We End that for reason able ranges of the parameters, the pseudo Goldstone bosons afford dominate contribution, the correction arising from new gauge bosons is negligibly small, the maximum of the relative corrections is similar to 10% with the center-of-mass energy roots- = 500 GeV; whereas in the case of roots- = 1500 GeV, the relative corrections could be up to 16%. Thus large new physics might be observable at the experiments of next-generation linear colliders.

Associated production of a neutral top-Higgs with a heavy-quark pair in the γγ collisions at ILC

We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in γγ collisions at the International Linear Collider (ILC). We find that the cross section for tht in γγ collisions is at the level of a few fb with the am. energy √s = 1000 GeV, which is consistent with the results of the cross section of tH in the standard model and the cross section of tth in the minimal supersymmetric standard model. It should be clear that hundreds of to thousands of ht per year can be produced at the ILC. This process of γγ → tht is really interesting in testing the standard model and searching the signs of technicolor.We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in γγ collisions at the International Linear Collider (ILC). We find that the cross section for tt̄ht in γγ collisions is at the level of a few fb with the c.m. energy √ s = 1000 GeV, which is consistent with the results of the cross section of tt̄H in the standard model and the cross section of tt̄h in the minimal supersymmetric standard model and the littlest Higgs models. It should be clear that hundreds of to thousands of ht per year can be produced at the ILC. This process of γγ → tt̄ht is really interesting in testing the standard model and searching the signs of technicolor.

Rare Decays and in the ,Topcolor-Assisted Technicolor Model*

We calculate the contributions to the rare decays and from one-loop -penguin diagrams in the framework of topcolor-assisted technicolor model. Within the parameter space, we find that: (a) the new contribution from technipions is less than 2% of the standard model prediction; (b) the top-pions can provide a factor of 10 to 30 enhancement to the ratios in question; (c) the topcolor-assisted technicolor model is consistent with the current experimental data.

Searches for the technicolor signatures via gg → W±πt∓ at the Large Hadron Collider

In this paper, we calculate the production of a charged top pion in association with a W boson via gg fusion at CERNs Large Hadron Collider in the context of the topcolor assisted technicolor model. We find that the total cross section of pp → gg → W±πt is several dozen femtobarns with reasonable values of the parameters, and the total cross section of pp → W±πt can reach a few hundred femtobarns when we consider the sum of the contributions of these two parton subprocesses, gg → W±πt and b → W±πt.

Searching for Flavor-Changing Neutral-Current Signals via e+e− (γγ) → tc̄h0t 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 (h0t) are predicted at tree level. We study the relevant processes of e+e− (γγ) → th0t at the International Linear Collider (ILC). It is found that these rare processes production rates can he enhanced significantly in the TC2 model. Especially for the process γγ → th0t, 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 mh0t < 2mt, 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.

New Physics Effects on Rare Decays B+u → π+ℓ+ℓ−, ρ+ℓ+ℓ− in a Top Quark Two-Higgs-Doublet Model

Using the form factors from light-cone sum rules, we study the branching ratios and forward-backward asymmetries (FBAs) of the exclusive decays B+u → π+l+l− and B+u → ρ+l+l− (l = e,μ) in the standard model (SM) and the top quark two-Higgs-doublet model (T2HDM). From the numerical results, we find that the new physics contributions cannot provide very large enhancement to the branching ratios and the theoretical predictions are in good agreement with the SM ones. The T2HDM effects on FBAs of these decays are small. Precision measurements of the dilepton invariant mass distributions, especially in the lower dilepton mass region, and the FBAs in the decays B+u → π+ (ρ+)l+ l− will greatly help in discriminating among the SM and the new physics models.

Constraints on Technicolor Models from Inclusive Decay of B Meson

Corrections to the branching ratio BR(B → Xsγ) from technipions and top pions appeared in technicolor models are investigated. We found that: (a) the multiscale walking technicolor model is ruled out since it is conflict with the CLEO data; (b) the topcolor-assisted technicolor model is consistent with the CLEO data of BR(B → Xsγ) for a certain range of parameters.

The Signatures of the Neutral Top-Pion at the NLC and the Tevatron in Topcolor-Assisted MWTC Model*

The neutral top-pion can couple to the gluons and the photons through the top quark triangle-loop. we calculate the corrections of the neutral top-pion to the production cross section in topcolor-assisted multiscale walking technicolor model. We find that, for a heavy neutral top-pion, the corrections are quite significant. For , and , the relative correction is larger than 10% which might be observed at a high-luminosity Tevatron. We further estimate the production cross section of at the NLC experiment. We find that the production rate is significantly large. The neutral top-pion may be detected in future linear collider experiments.