Top-Quark FCNC Decay t-cgg in Topcolor-assisted Technicolor(3)

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

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