Mediation of Supersymmetry Breaking in Gauge Messenger Model(18)

We study gauge mediation of supersymmetry breaking in SU(5) supersymmetric grand unified theory with gauge fields as messengers. The generated soft supersymmetry breaking parameters lead to close to maximal mixing scenario for the Higgs mass and highly red

xedbygrouptheoreticalfactors.ThemainfeaturesofthespectrumdonotchangewhenconsideringmorecomplicatedGUTmodelsthantheminimalscenariowefocusedoninthispaper.And nally,consideringcontributionsfromgravitymediationnotonlyopensapossibilitytogeneratetheµtermthroughtheGiudice-Masieromechanism,butalsocanleadtomanyvariationoftheminimalscenariowithinterestingconsequencesforongoingandfutureSUSYanddarkmattersearches.

TheLSPinthismodelisthelightestneutralino(inalimitedregionofparameterspace)whichisasizablemixtureofbino,winoandhiggsino,orgravitino(inmostregionofparameterspace)withsneutrinoorstopNLSP.StauNLSPmightbedetectableusingstopperandsimilarlyforstopNLSP,butadetailedstudyisneeded.InthecaseofstopNLSPitisimportanttoclarifywhethersuchascenarioisconsistentwithBBN.

Themodelpredictslightstop,mt 1> >～150GeV,andlightgluino,mg～400GeV,intheleast netunedregionofparameterspace.LightgluinoshouldbeeasytoseeattheLHCorevenattheTevatron.Inspiteofstopbeingconsiderablylighterthanothersquarks,itmightbeeasiertosearchforthe rsttwogenerationsofsquarksattheTevatron.Indeed,recentresultsfromD0andCDFcollaborations[44,45],forjets+missingtransverseenergysearch,putstrongconstraintsonmassesofthe rsttwogenerationsofsquarksandthegluinomass,intherange～300 400GeV.Theselimitswillfurtherimproveinnearfuture.Atthispointwewouldliketonotethattheresultsofbothcollaborationsarepresentedinmq –mg planeformSUGRAscenarioandexclusionlimitscoveronlygluinomasseslittlelargerthansquarkmassesbecauseotherwisethereisnomSUGRAsolution.However,squarksquitelighterthangluinoarewellmotivatedbynaturalEWSB.Inthemodelpresentedheremassesofgluinoandthe rsttwogenerationsofsquarkslieveryneartheborderwithnomSUGRAsolution,and,aswediscussed,modelsthatwouldfurtherimproveonnaturalness(withmorenegativestopmassessquaredattheGUTscale)wouldleadtosquarksevenlightercomparedtogluino.ThereforewestronglyencouragebothD0andCDFcollaborationstoextendthesearchandexplorefullkinematicallyallowedregioninthesquark-gluinoplanesothatalsothesescenariosarecoveredinadditiontothenotsonaturalone.

ConsiderationsofnaturalEWSBinMSSMtogetherwiththecurrentexperimentallimitsonSUSYandHiggsspectraleadustoconclusionsthatSUSYspectrummightbequitestrangeandperhapscomplicated(notunifyingatanyscale)comparedtotheusualexpectationsbasedonmodelslikemSUGRA,andthatthereisagoodchanceweliveinameta-stablevacuum.However,asweshowed,theseseeminglyunattractivefeaturesmightbeaconsequenceofthesameelegantideathatleadstoanunderstandingofquantumassignmentsofstandardmodelparticlesandgaugecouplinguni cation.

Acknowledgement

WethankK.Agashe,K.Choi,J.Ellis,G.Giudice,A.Kusenko,K.-I.Izawa,K.-I.Okumura,M.Peskin,S.RabyandN.Weinerfordiscussions.HKthankstheGalileoGalileiInstituteforTheoreticalPhysicsandCERNforhospitalityandtheINFNforpartialsupportduringthework.IKthanksLBNLforhospitalityduringhisvisit.RDissupportedinpartby

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