The Role of Antimatter Searches in the Hunt for Su

arXiv:hep-ph/0406018v221Sep2004PreprinttypesetinJHEPstyle-HYPERVERSIONSISSA-37/2004/EPTheRoleofAntimatterSearchesintheHuntforSupersymmetricDarkMatterStefanoProfumoandPieroUllioSISSA/ISAS,viaBeirut2-4,34013Trieste,ItalyandIstitutoNazionalediFisicaNucleare,Sez.diTrieste,34014Trieste,ItalyE-mail:[e-mail],[e-mail]:Weanalyzetheantimatteryieldofsupersymmetric(SUSY)modelswithlargeneutralinoannihilationcrosssections.Weintroducethreebenchmarkscenarios,respec-tivelyfeaturingbino,winoandhiggsino-likelightestneutralinos,andwestudyindetailtheresultingantimatterspectralfeatures.Wecarryoutasystematicandtransparentcomparisonbetweencurrentandfutureprospectsfordirectdetection,neutrinotelescopesandantimattersearches.Wedemonstratethatoften,inthemodelsweconsider,antimat-tersearchesaretheonlydetectionchannelwhichalreadyconstrainstheSUSYparameterspace.Particularlylargeantiprotonsfluxesareexpectedforwino-likelightestneutralinos,whilesignificantantideuteronfluxesresultfromresonantlyannihilatingbinos.Weintro-duceasimpleandgeneralrecipewhichallowstoassessthevisibilityofagivenSUSYmodelatfutureantimattersearchfacilities.Weprovideevidencethatupcomingspace-basedex-periments,likePAMELAorAMS,aregoingtobe,inmanycases,theuniqueopenroadtowardsdarkmatterdiscovery.Keywords:SupersymmetryPhenomenology,DarkMatter,Antimatter.Contents1.Introduction12.Theparticlephysicsframework32.1Relicabundance,acceleratorconstraintsandWIMPmodels32.2Thethreebenchmarkscenarios53.Indirectsearchesthroughantimattercosmicraymeasurements93.1Estimatesoftheantimatterfluxes93.2Antimatterspectralfeaturesforthethreebenchmarkmodels114.Currentexclusionlimits134.1TheAMSBmodel164.2TheFunnelandtheNUGMmodels185.ProspectsforSUSYDMdetectionthroughantimattersearches195.1Discriminationperspectivesatfutureantimattersearchexperiments195.2Futuresearchstrategiesandtheroleofantimatter236.Thehalomodeldependence257.Conclusions291.IntroductionWeaklyinteractingmassiveparticles(WIMPs)areamongtheleadingcandidatesforcolddarkmatterintheUniverse:ononeside,theideaisappealingsincedarkmatterappearsjustasanotherofthethermalleftoversfromtheearlyUniverse;atthesametime,fromtheparticlephysicspointofview,numerousmodelsnaturallyembedsuchkindofparticles.ThesearchforWIMPshasthereforebeenoneofthehottopicsinexperimentalphysicsoverthelastdecadeorso,andthefieldisnowacquiringnewperspectiveswithnext-generationexperimentsbeingattheresearchanddevelopmentstage,or,insomecases,evenclosertothedatatakingphase.ThetargetiseithertodetectWIMPsdirectly,measuringtherecoilenergyfromWIMPselasticscatteringonnuclei,ortosearchfortheyieldsofWIMPpairannihilations,suchasneutrinosfromtheEarth/Sunorcosmicraysfromannihilationsinthegalactichalo.Complementaritybetweendirectdetectionandindirectdetectionmethodshasbeenrepeatedlystressed(forreviewsonthistopic,see,e.g.,[1,2]).Indeed,theideaofWIMPdarkmatterreferstoabroadframeworkratherthantoanyspecificmodel;insuchaframework,anoverall(weak)couplingofdarkmattertoordinarymatterisguaranteed,–1–butdetailsonhowsuchcouplingisrealizedmaybesensiblydifferentfromonemodeltoanother:Oneofthemostpressingissuesfromanexperimentalistperspective,thequestionregardinghowcompetitiveagivendetectiontechniqueiscomparedtotheothers,canbeaddressedjustonmodeldependentgrounds.ThemostpopularWIMPdarkmattercandidateisthelightestneutralinoinsupersym-metricextensionsofthestandardmodelofparticlephysics.Theideaofsupersymmetryhasstrongtheoreticalmotivations,butithas,unfortunately,noexperimentalconfirmationsofar.Recipesonhowtointroduceasupersymmetricmodel(andhencethecorrespond-ingdarkmattercandidate)haveratherweakconstraints;tosomeextent,thisfreedomiseventoolarge,sothat,forpracticalpurposes,itiscustomarytofocusonminimalmodels,i.e.modelswithminimalparticlecontentandasmallnumberoffreeparameters.ThebenchmarkscenariomostoftenimplementedisthemSUGRAsetup,i.e.thesupergravityinspiredmodelwiththesmallestpossiblenumberoffreeparameters,namelyonlyfourparametersandonesign,partlydefinedatthegrandunification(GUT)scaleandpartlyatthelowenergy(electroweak)scale.Referring,withinthisframework,tomodelswithathermalrelicdensity(inastandardsetup)matchingthecolddarkmattertermasdeducedfromlatesthighprecisioncosmologicalmeasurements[3],prospectsfordirectdetectionlookmorepromisingthanthoseforindirectdetectionmethods(see,e.g.,therecentanal-ysisinref.[4]).Tosomeextent,asimilarconclusionisreachedalsoforthermalrelicmodelsinthecontextofminimalsupersymmetricstandardmodel(MSSM)setupsdefinedbyfewuniversalparameterchosenatalowenergyscale(suchasthesevenparametermodelimplemented,e.g.,inref.[5]).Thereisoften,intheliterature,thetendencytoextrapolateontheseresults,andassumethat,asagenerictrendforsupersymmetricdarkmattercandidates,directdetectionshouldhavetoppriority.Wegivehereafewcounterexamples,stillinthecontextofminimalsupersymmetricsetups,whichallowforaclearerpresentationofresultsandamoretransparentcomparisonbetweendifferentsignals(forrelatedstudieswithinvarioussupersymmetrybreakingsce-nariossee,e.g.,[6]).Wewillenlighten,inparticular,theroleofindirectdetectionthrou