Decays Z --> ggg and Z-prime --> ggg in the minimal 331 model

We perform a complete calculation at the one-loop level for the Zggg and Zggg couplings in the context of the minimal 331 model, which predicts the existence of a new Z gauge boson and new exotic quarks. Bose symmetry is exploited to write a compact and manifest SU_C(3)-invariant vertex function for the Vggg (V=Z,Z) coupling. Previous results on the $Zto ggg$ decay in the standard model are reproduced. It is found that this decay is insensitive to the effects of the new exotic quarks. This in contrast with the $Zto ggg$ decay, which is sensitive to both the standard model and exotic quarks, whose branching ratio is larger than that of the $Zto ggg$ transition by about a factor of 4.

Implications of $D^0-overline{D^0}$ on the rare top quark decays $tto ugamma$ and $tto ug$

The recently observed mass difference of the $D^0-overline{D^0}$ mixing is used to predict the branching ratios of the rare top quark decays $tto ugamma$ and $tto ug$ in a model independent way using the effective Lagrangian approach. It is found that $Br(tto ugamma)<4times 10^{-4}$ and $Br(tto ug)<2times 10^{-3}$, which still may be within reach of the LHC collider.

Effective Lagrangian description of Higgs mediated flavor violating electromagnetic transitions: implications on lepton flavor violation

Higgs mediated flavor violating electromagnetic interactions, induced at the one--loop level by a nondiagonal $Hf_if_j$ vertex, with $f_i$ and $f_j$ charged leptons or quarks, are studied within the context of a completely general effective Yukawa sector that comprises $SU_L(2)times U_Y(1)$--invariant operators of up to dimension--six. Exact formulae for the one--loop $gamma f_if_j$ and $gamma gamma f_if_j$ couplings are presented and their related processes used to study the phenomena of Higgs mediated lepton flavor violation. The experimental limit on the $mu to egamma$ decay is used to derive a bound on the branching ratio of the $mu to egamma gamma$ transition, which is 6 orders of magnitude stronger than the current experimental limit. Previous results on the $tau to mu gamma$ and $tau to mu gamma gamma$ decays are reproduced. The possibility of detecting signals of lepton flavor violation at $gamma gamma$ colliders is explored through the $gamma gamma to l_il_j$ reaction, putting special emphasis on the $tau mu$ final state. Using the bound imposed on the $Htau mu$ vertex by the current experimental data on the muon anomalous magnetic moment, it is found that about half a hundred events may be produced in the International Linear Collider.

Higgs mediated lepton flavor violating tau decays $tau to mu gamma$ and $tau to mu gamma gamma$ in effective theories

The size of the branching ratios for the $tau to mu gamma$ and $tau to mu gamma gamma$ decays induced by a lepton flavor violating Higgs interaction $Htau mu$ is studied in the frame of effective field theories. The best constraint on the $Htau mu$ vertex, derived from the know measurement on the muon anomalous magnetic moment, is used to impose the upper bounds $Br(tau to mu gamma)<2.5times 10^{-10}$ and $Br(tau to mu gamma gamma)<2.3times 10^{-12}$, which are more stringent than current experimental limits on this class of transitions.