The lepton flavor violating decays $Zto l_i l_j$ in the simplest little Higgs model

In the simplest little Higgs model the new flavor-changing interactions between heavy neutrinos and the Standard Model leptons can generate contributions to some lepton flavor violating decays of $Z$-boson at one-loop level, such as $Z to tau^{pm}mu^{mp}$, $Zto tau^{pm}e^{mp}$, and $Z to mu^{pm}e^{mp}$. We examine the decay modes, and find that the branching ratios can reach $10^{-7}$ for the three decays, which should be accessible at the Giga$Z$ option of the ILC.

Rare Z-decay into light pseudoscalar bosons in the simplest little Higgs model

The simplest little Higgs model predicts a light pseudoscalar boson $eta$ and opens up some new decay modes for $Z$-boson, such as $Z to bar{f} f eta$, $Zto etaetaeta$, $Zto etagamma$ and $Zto eta gg$. We examine these decay modes in the parameter space allowed by current experiments, and find that the branching ratios can reach $10^{-7}$ for $Zto bar{b}beta$, $10^{-8}$ for $Zto bar{tau}taueta$, and $10^{-8}$ for $Zto etagamma$, which should be accessible at the GigaZ option of the ILC. However, the branching ratios can reach $10^{-12}$ for $Zto etaetaeta$, and $10^{-11}$ for $Zto eta gg$, which are hardly accessible at the GigaZ option.

R_b Constraints on Littlest Higgs Model with T-parity

In the framework of the littlest Higgs model with T-parity (LHT), we study the contributions of the T-even and T-odd particles to the branching ratio R_b. We find that the precision data of R_b can give strong constraints on the masses of T-odd fermions.

Higgs-pair Production and Decay in Simplest Little Higgs Model

In the framework of the simplest little Higgs model (SLHM), we study the production of a pair of neutral CP-even Higgs bosons at the LHC. First, we examine the production rate and find that it can be significantly larger than the SM prediction. Then we investigate the decays of the Higgs-pair and find that for a low Higgs mass their dominant decay mode is hh->etaetaetaeta (eta is a CP-odd scalar) while hh->bbar{b}etaeta and hh->etaeta WW may also have sizable ratios. Finally, we comparatively study the rates of pp-> hh -> bbar{b}tau^+ tau^-, pp->hh->bbar{b}gammagamma, and pp->hh->WWWW in the SLHM and the littlest Higgs models (LHT). We find that for a light Higgs, compared with the SM predictions, all the three rates can be sizably enhanced in the LHT but severely suppressed in the SLHM; while for an intermediately heavy Higgs, both the LHT and SLHM can enhance sizably the SM predictions.