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
Introduction:TheupcomingLargeHadronCollider(LHC)willputvariousnewphysicsideastothesword.WhilethismachinehasenoughenergytoproduceTeV-scalenewparticlesandthuscandirectlyprobeTeV-scalenewphysics,oneshouldalsopaysu cientattentiontotheindirectprobethroughrevealingquantume ectsofnewphysicsinsomesensitiveprocesses.AstheheaviestfermionintheStandardModel(SM),thetopquarkisspeculatedtobeasensitiveprobeofnewphysics[1].SofarthetopquarkpropertiesarenotpreciselymeasuredduetothesmallstatisticsoftheexperimentsattheFermilabTevatroncollider.TheLHCandtheproposedInternationalLinearCollider(ILC)willcopiouslyproducetopquarksandallowtoscrutinizethetopquarknature.
OneofthepropertiesofthetopquarkintheSMisitsextremelysmall avor-changingneutral-current(FCNC)interactions[2]duetotheGlashow-Iliopoulos-Maiani(GIM)mech-anism.ThiswillmaketheobservationofanyFCNCtopquarkprosessarobustevidencefornewphysicsbeyondtheSM.Sofarnumerousstudies[3]haveshownthattheFCNCtopquarkinteractionscanbesigni cantlyenhancedinsomenewphysicsmodelsliketheminimalsupersymmetricmodel(MSSM)[4,5,6]andtheTC2model[7,8].ItwasfoundthatfortheseFCNCtopquarkprocessestheTC2modelusuallyallowsformuchlargerproductionordecayratesthanthesupersymmetricmodel.ThroughthemeasurementsoftheFCNCtopquarkprocessesattheLHCorILC,thee ectsofthesenewphysicsmodelswillberevealed.
AlthoughsofarintheliteraturethereareseveralworksdevotedtotheTC2contributionstotheFCNCtopquarkdecays,theTC2predictionforthethree-bodydecayt→cgghasnotbeenstudiedyet.Asshownin[2,4],inboththeSMandMSSMthisdecayisfoundtohavealargerbranchingratiothanthetwo-bodydecayt→cgandthusmaybethemosthopefulFCNCtopdecaychanneltodiscoverattheLHCorILC.InthisworkwefocusontheTC2contributiontothisdecayandcompareitsbranchingratiowitht→cg.
Thisworkisorganizedasfollows.Wewill rstdiscusstheTC2modelandthenperformthecalculations.Sincethecalculationsinvolvemanyloopsandaresomewhattedious,wewillnotpresentthedetailsandwillinsteadgivetheanalyticalresultsinanappendix.WewillpresentsomenumericalexampleswithcomparisontotheresultsintheSMandMSSM,and nallygiveourconclusion.
Calculations:BeforeourcalculationswerecapitulatethebasicsoftheTC2model.