The topcolor-assisted technicolor (TC2) model predicts several pseudo-scalars called top-pions and at loop level they can induce the FCNC top quark decay t->cgg which is extremely suppressed in the Standard Model (SM). We find that in the allowed parameter
t=t+t+t
FIG.1:Feynmandiagramsforthee ectivevertextc¯gatone-looplevelinTC2model.Thebosonineachloopdenotesaneutraltop-pion,atop-Higgsorachargedtop-pion,whilethefermionineachloopiscorrespondinglyatoporbottomquark.
Asiswellknown,thefancyideaoftechnicoloraimstodynamicallybreaktheelectroweaksymmetry,butitencountersenormousdi cultyingeneratingfermionmasses,especiallytheheavytopquarkmass.TheTC2model[9]combinestechnicolorwithtop-color,withtheformerbeingresponsibleforelectroweaksymmetrybreakingandthelatterforgeneratinglargetop-quarkmass.ThismodelsofarsurvivescurrentexperimentsandawaitsbeingtestedattheLHC.
AcrucialaspectofTC2phenomenologywillberelatedtothelightpseudo-Goldstonebosonscalledthetop-pions(π0tandπ±t),whicharepredictedinTC2modelattheweakscale[9]andhave avor-changingcouplingswiththetopquark
(1 )mt√
2Ftv iKULttKURtt¯tLtRπ0t+iKULttKURtc¯tLcRπ0t
+√2KURtcKDLbbc¯RbLπ t
+KULttKURtt¯tLtRh0t+KULttKURtc¯tLcRh0t+h.c. ,(1)
wherethefactor
m=1 ,K2 2,(2)
tURtc≤
withm′tdenotingthetop-colorcontributiontothetopquarkmass.
assumeKURtc= Inourcalculationswe