research-statement的范例-jiangyun.pdf
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research-statement的范例-jiangyun.pdf
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ResearchStatementYunJiangPh.D.candidateinPhysicsatU.C.Davis2013LHC-TIGraduateFellowMycurrentresearchconcentratesonLargeHadronCollider(LHC)phenomenology,especiallythatrelatedtoHiggsphysicsanddarkmatter.Thephenomenologyofthe125.5GeVHiggsboson,whichwasdiscoveredattheLHC,inthenext-to-minimalsupersymmetricstandardmodel(NMSSM)andtwo-Higgs-doubletmodel(2HDM)hasconstitutedthemainpartofmyworktowardsmyPh.D.degree.Iamintheprocessofexpandingmyresearchworktoincludethetopicsofextradimensionsandinflationoftheearlyuniverse.AccomplishedworkWefirstassessedtheextenttowhichvarioussemi-constrainedNMSSM(scNMSSM)scenarioswitha125GeVlightestCP-evenHiggsh1areabletodescribetheLHCsignal.Wefoundthatenhancedratesaremostnaturalwhentheh1hasmasssimilartothesecondlightestCP-evenHiggs,h2,withenhancementparticularlylikelyiftheh1andh2aredegenerate.Toexperimentallyprobethispossibility,wedevelopeddiagnostictoolsthatcoulddiscriminatewhetherornottherearetwo(ormore)HiggsbosonsversusjustonecontributingtotheLHCsignalsat125.5GeV.Inaddition,weconsideredthecasewherethelightestHiggsh1providesaconsistentdescriptionofthesmallLEPexcessat98GeVwhereastheheavierHiggsh2possessestheprimaryfeaturesoftheLHCHiggs-likesignalsat125GeV.BesidestheNMSSMstudies,the2HDM,oneofthesimplestextensionsoftheHiggssector,isanotherfocusofmyresearchwork.WerecentlyperformedanexhaustiveanalysisforTypeIandTypeIImodelstoaddressanimportantquestion:
towhatextentarethelatestmeasurementsofthe125.5GeVHiggs-likesignalattheLHCcompatiblewiththe2HDM,assumingthattheobserved125.5GeVstateisoneofthetwoCP-evenHiggsbosons?
Wealsodiscussedtheimplicationsforfuturecolliders,includingexpectationsregardingotherlighterorheavierHiggsbosons.Inanearlierstudy,weexaminedthemaximumHiggssignalenhancementsthatcanbeachievedinthe2HDMinwhicheitherasingleHiggsbosonormultipleHiggsbosonshavemass(es)near125.5GeV.Wefoundthattheconstraintsrequiringvacuumstability,unitarityandperturbativitysubstantiallyrestrictpossibilitiesforsignalenhancement.Furthermore,weextendthe2HDMbyaddingarealgauge-singletscalar(2HDMS),whichcouldbestableundertheextraZ2symmetryandtherebyapossibledarkmatter(DM)candidate.Comparingwiththesimplestsingletextensionthismodelhasricherphenomenology.ForheavyDM(massabove55GeV)whichgeneratesthedesiredrelicabundance,thepredictedcrosssectionforDM-nucleonscatteringisbelowthecurrentLUXlimitandeventhefutureXENON1Tprojection.Incontrast,thismodelcanaccommodatelightDM,eveniftheconstraintonHiggsinvisibledecayistakenintoaccount,anddescribetheCDMSIIandCoGeNTpositivesignalregions.Moreimpressively,thetensionwiththeLUX/SuperCDMSexclusioncanbealleviatedintheTypeII2HDMSinwhichtheDM-nucleoninteractioncouldbeisospin-violating.Intheprocessofcompletingthisproject,weindependentlyworkedoutthemodelfilesfortheFeynRulesprogramandwillmakethemodeldatabasepubliclyavailablesoon.OngoingprojectsBasedonthecomprehensivestudieswehaveaccomplished,wefocusonthelight(pseudo)scalarHiggsbosonregioninthe2HDM.WearealsopursuingwhetherthecurrentLHC8TeV-rundatapushesthe2HDMtothealignmentlimitand/orthedecouplinglimit.Inthemeanwhilewearedevelopingaroutinetosimplifythecalculationforgluon-fusionandbottom-quarkassociatedproductioncrosssections.Besides,weconsiderthedecoupling2HDMtodetermineifthevacuumcouldbestableabovetheinflationorGUTscale,assumingthe2HDMisalow-energyeffectivetheory.Ifitisstable,thentheinflationdrivenbythe2HDMHiggswouldbepossibleandatopicforfuturestudy.Oneofthemostimportantextensionsofthestandardmodel(SM)istheinclusionofadditionalparticle(s)thatcomprisetheDMoftheuniverse.SofaranumberofcollaborationshavebeendevotedtoworkingonthedirectdetectionofDM.TheytypicallytranslatethelimitontheeventrateagainstrecoilenergytheydirectlydetectintoalimitontheDM-protoncrosssectionasafunctionofDMmass.However,thereareseveralstandardassumptionshiddeninthistranslationthatmightnotbecorrect.Inparticular,itisnormallyassumedthatDMhasequalcouplingtoneutronsandprotons.Infact,thetensionbetweenthenullLUX/SuperCDMSexclusionsandthepositivesignalregionsfavoredbyCDMSIIandCoGeNTcouldbealleviatediftheDMinteractionswithnucleonsareallowedtoviolateisospinsymmetry.Thus,wearenowinterestedinexploringthepossibilitiesofalightisospin-violatingDM(IVDM)inthe2HDMSandNMSSMeventhoughsuchanisospin-violationeffectinsupersymmetry(SUSY)modelshasbeenclaimedtobenegligible.Ifpresent,suchlightannihilatingIVDMmayexplaintheoriginoftheexcessofgammarayfluxfromthegalacticcenter,asindicatedinthepreviousstudies.YunJiang,Ph.D.ResearchStatement2AnotherprojectIamnowinvolvediniswarpedDM.InviewofthesuccessofextradimensionsinresolvingthehierarchyandflavorproblemsoftheSM,wearestudyingDMinwarpedextradimensionsinparticularwithRandall-Sundrumlikegeometries.WeconsiderthecasethatallSMfieldsliveinthebulk.InourmodelthefirstHiggsexcitedstateisapossiblestableDMcandidateduetothepresenceofageometricKK-parity.OurfocusisonphenomenologicalimplicationsoftheDMafterimposingconstraintsfromcurrentexperimentaldata.FutureplanInthenearfutureIwillcontinueinvestigatingLHCimplicationsofvariousHiggsmodelsbeyondtheSMbothwithinandoutsidetheframeworkofSUSY.Potentialextensionstomypreviousstudiesincludethefutureprospectsof2HDMatthe100TeVcolliderandtherelatedanalysesintheframeworkofphenomenologicalNMSSM,aversionofNMSSMwithoutGUT-scaleunificationassumptions.Additionally,darkmatterphysicsandinflationoftheearlyuniversedrivenbytheHiggsboson,HiggsportalDM,axion,etc.willbeimportanttopicsofexplorationinmypost-doctoralresearch.Itiswell-knownthatHiggsinflationisunlikelytooccurwithinthepureSMgiventhelatestLHCmeasurementonthetopquarkmass.Toremedythisissue,IamconsideringtheadditionalloopcontributionfromHiggsportalinteractionstoraisethetensor-to-scalarratioattheinflationscale.AnotherprobabledirectionofmyfutureworkisinHiggstripletandneutrinophysics.IwishtoconstructamodelthatcontainsaLHCobservedHiggsandaDMcandidateandisalsoabletoexplaintheneutrinomassbymeansofType-IIseesawmechanism.Ratherthanbeingtheendofthestory,thediscoveryofthe125.5GeVHiggsbosonhasmarkedanewerainparticlephysics.IanticipatethatthisdiscoverywillprovideakeywindowintotheoriesbeyondtheSM,andthatadditionalHiggsbosonsandSUSYparticlesmaywellbefound.Avarietyofongoingexperimentsaimedatdetectingdarkmatterwilleitherprovidefurtherlimitsorsucceedindetectingdarkmatter.Eitherway,DMmodelswillbeconstrainedand/oreliminated,therebyprovidingguidancetoongoingtheoreticalwork.Asayoungresearcher,Iamfortunatetobeinthemidstofanexcitingtimeandwillcertainlyworkextremelyhardtocontributetoourhighenergyphysicscommunity.YunJiang,Ph.D.ResearchStatement3
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