Mediation of Supersymmetry Breaking in Gauge Messenger Model(4)

canbereducedtothelevelof10%.Besidesexcludedregionsthatalreadyappearedinthecaseofpuregaugemediation,Fig.2,thereisalsoaregionexcludedbylimitsonthestopmass.Thisisduetoasubtlee ectoflargermHuintheevolutionofstopmasses

squared.Stopmassessquaredruntoslightlysmallervalueswhichincreasesstopmixingandconsequentlyleadstomuchsmallervalueofthelighteststopmasseigenstate.Forthesamereason,besidesneutralino(N)LSPandstauNLSP,thereisaregionwithstopNLSP.TheNLSPsituationcanbeeasilychangedwhenconsideringcontributionfromgravitymediationalsotosquarksandsleptons.

4.3Othercases

Addingauniversalcontributiontoallscalarmassesfromgravitymediationhasanegligiblee ectontheEWscalevalueofm2Hu.ThiscanbeeasilyseenfromEq.(2.2)inwhichthe2approximatelycanceleachotherform2=m2=m2atthetermscontainingm20 HuHuandmttGUTscale.Therefore,addingm0(unlessitisverylarge)doesnotchange netuningofEWSB.Thecontributionfromm0alsomakesstopsheavierandreducesthemixing.ThisreducestheHiggsmassandsoonlysmallvaluesofm0areallowedforsmallMSUSY–theregionweareinterestedin.Smallm0ishoweversu cienttochangetheNLSPofamodel.Forsmallertanβitcanhighlyenlargetheregionwhereneutralinois(N)LSPinsteadofsneutrinoorstop,andforlargertanβitcanbasicallyeliminatetheregionwherestopisNLSP.

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

Hu

c

10102020303040

M

Figure4:Allowedregionofparameterspaceandthedegreeof netuningintheMSUSY cHuplaneforgaugemediation,Nmess=0andbG=3,withacontributionfromgravitymediationintheHiggssector.We xtanβ=25andcHd=50.0.Themeaningofexcludedregionsisthesame

1andτasinFig.2.Theblackdashedlineseparatesregionswheret 1areNLSP.

SofarwehavediscussedonlythecasewithNmess=0andbG=3.InFig.5we

alsopresentplotsofrenormalizationgrouprunningofsoftSUSYbreakingparametersforNmess=0andsmallervaluesofbGwhichcorrespondtoaddingmorecontenttotheminimalGUTscenario.Andforcompleteness,inthesame gurewealsoincludeNmess=1,bG=2casewhichcorrespondstotheminimalGUTcontentwithonepairofadditionalvector-likemessengersin5and¯5ofSU(5).InallcasesMSUSYandtanβare xedtothesamevaluewhichallowsustoseetrendsinthespectrumfromchangingthecontentofamodel.Forexactlythisreasonwedonotrequirethatalltheexperimentallimitsaresatis edinallmodels.Detailedinformationaboutthese vepointsisgiveninthelast vecolumnsinTable1.Thebasicfeaturesofallpresentedcasesareverysimilar.LoweringbGresultsinlightersquarkandsleptonspectrumbutslightlylargerstopmixing.Asaresult,theHiggsmassisdecreasingveryslowly.Addingadditionalpairofmessengerleadstolighterspectrumbecauseofthecancelationbetweencontributionsfromgaugemessengersandvector-likemessengersandthusinorderforthisscenariotobeviable,largerMSUSYisneeded.Wedonotdiscusspossibleadditionofgravitymediationforthesescenarios.

4.4LSPandNLSP

WhenthereisasizablecontributiontotheHiggssoftparametersfromgravitymediation,neutralinocanbeLSPorNLSPdependingonthegravitinomass.Inthisregion,neutralino

50606070708090 (GeV)SUSY

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

isasizablemixtureofbino,winoandHiggsino.Sizablemixtureofbinowithhiggsino/winocangivetherightamountofthermalrelicdensityfordarkmatterwhenµ,M1andM2areoforder100GeV.Inaddition,thecrosssectionforthedirectdetectionislargercomparedtobinoLSPwhichgivesabetterchancetoobserveit.

Inmostregionofallowedparameterspace,sneutrino/stauorstopisNLSPandtheLSPisthegravitino.GravitinoLSPscenariowiththeright-handedstauNLSPhasbeenstudiedintheframeworkofsupergravity[36][37][38][39][40][41].ThelifetimeofthestauNLSPisfrom106secto1010secandwemightbeabletodetectitusingastopper.Asweprovideaspeci cmodelinwhichthegravitinoLSPisveryplausible,wecangetamoreconcretepredictiononNLSPlifetimeandgravitinorelicdensity.SimilaranalysisshouldbedoneforthestopNLSP.

>Thegaugemessengermodelconsideredheregenerallypredictsaverylightstop,mt 1～150GeVintheleast netunedparameterspace.TheFig.4showsthatstopbecomes

NLSPifcHu 30.StopNLSPhasbeenstudiedin[35]intheframeworkoflowscalegauge

mediation.Whengravitinoisverylight,thedecayofstopNLSPcanhappenquickly,withinaminute,andthesearchforapossiblecollidersignalcanbedone.Ifgravitinomassisataroundtheweakscale,stopdecayslongafterthebigbangnucleosynthesis(BBN).UsuallydecaysofparticleshavinghadronicchannelsdestroythesuccessfulagreementofBBNandsuchscenariosarenotconsidered.6NonethelessthedetailedanalysisofstopdecayafterBBNshouldbedonetoclearupthisissue.IfstopNLSPwithweakscalegravitinomassisconsistentwithBBN,morenaturalparameterspaceisallowed.

5.Conclusions

InthispaperwestudiedgaugemediationofsupersymmetrybreakinginSU(5)SUSYGUTwithheavygauge eldsasmessengers.WewereledtoconsiderthisgaugemessengermodelbyrecentlydiscussedpossibilityofgeneratingthemaximalmixingscenariofortheHiggsmassradiatively[7].Intheoptimalscenariocoloredparticlesdonotcontributetotherenormalizationgrouprunningofthem2Huwhichinprinciplecaneliminate netuningofEWSB.Thegaugemessengermodeldoesnotleadtotheoptimalscenario(onlyclosetoit),sincestopmassesarenotnegativeenoughattheGUTscale.However,itstillhighlyreducesthe netuningofEWSBandhasmanyinterestingfeatures.

InthisscenarionegativescalarmassessquaredattheGUTscale,withsquarksmorenegativethansleptons,togetherwithnon-universalgauginomasses,withM1>M2>M3,leadtoaviablespectrumattheEWscaleinlargeportionofparameterspace.NoneofthesoftSUSYbreakingparametersattheGUTscalehastobelargerthan400GeVandnoneofthesuperpartnerhastobeheavierthan400GeVtosatisfyallthelimitsfromdirectsearchesforSUSYparticlesandalsothelimitontheHiggsmass.Thereisnootherexistingscenariow …… 此处隐藏：6287字，全部文档内容请下载后查看。喜欢就下载吧 ……