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Searching for Neutrinos from WIMP Annihilations in the Galactic Stellar Disk

Weakly interacting massive particles (WIMPs) are a viable candidate for the relic abundance of dark matter (DM) produced in the early universe. So far WIMPs have eluded direct detection through interactions with baryonic matter. Neutrino emission from accu

Mon.Not.R.Astron.Soc.000,000–000(0000)Printed9April2008

A(MNLTEXstyle lev1.4)

SearchingforNeutrinosfromWIMPAnnihilationsinthe

GalacticStellarDisk

arXiv:0804.0554v2 [astro-ph] 9 Apr 2008

ZachariaMyersandAdiNusser

PhysicsDepartment,Technion,Haifa32000,IsraelandtheAsherSpaceResearchInstitute

9April2008

ABSTRACT

Weaklyinteractingmassiveparticles(WIMPs)areaviablecandidatefortherelicabundanceofdarkmatter(DM)producedintheearlyuniverse.SofarWIMPshaveeludeddirectdetectionthroughinteractionswithbaryonicmatter.NeutrinoemissionfromaccumulatedWIMPannihilationsinthesolarcorehasbeenproposedasasigna-tureofDM,buthasnotyetbeendetected.ThesenullresultsmaybeduetosmallscaleDMdensity uctuationsinthehalowiththedensityofourlocalregionbeinglowerthantheaverage(~0.3GeV/cm3).However,theaccumulatedneutrinosignalfromWIMPannihilationsintheGalacticstellardiskwouldbeinsensitivetolocaldensityvariations.Insidethedisk,darkmattercanbecapturedbystarscausinganenhancedannihilationrateandthereforeapotentiallyhigherneutrino uxthanwhatwouldbeobservedfromelsewhereinthehalo.Weestimateaneutrino uxfromtheWIMPannihilationsinthestellardisktobeenhancedbymorethananorderofmagnitudecomparedtotheneutrino uxesfromthehalo.Weo eraconservativeestimateforthisenhanced ux,basedontheWIMP-nucleoncross-sectionsobtainedfromdirect-detectionexperimentsbyassumingadensityof~0.3GeV/cm3forthelocalDM.Wealsocomparethedetectabilityofthese uxeswithasignalofdi usehighenergyneu-trinosproducedintheMilkyWaybytheinteractionofcosmicrays(CRs)withtheinterstellarmedium(ISM).Thesecomparativesignalsshouldbeobservablebylargeneutrinodetectors.

Keywords:darkmatter,neutrinos,cosmic-rays,indirectdetection

1INTRODUCTION

Determiningthenatureofdarkmatteranddetectingithasremainedanoutstandingprobleminastrophysics.Forsev-eraldecades,signi cantevidenceinfavourofacolddarkmatteruniversehasaccumulatedfromobservationsofgalac-ticclustersandlarge-scalestructure(Davisetal.1985),su-pernovae(Perlmutteretal.1999)andthecosmicmicrowavebackground(CMB)anisotropies(Bennettetal.2003).ItisbelievedthatifWIMPspopulatethehalooftheMilkyWaytoday,thentheycouldbedetectedviadirectWIMP-nucleoninteractions.Experimentsfordirectdetectionarecurrentlyunderway,e.g.PICASSO(Barnab-Heideretal.2005),CDSM(Akeribetal.2006),SIMPLE(Alneretal.2005),NAIAD(Girardetal.2005),andDAMA(Bernabeietal.2008).Unfortunately,todate,nosuchdirectinterac-tionshavebeenobserved.However,thesedirectdetectionexperimentshavebeenusedforplacingstringentlimitsontheWIMP-nucleoncross-section.Theselimitsareobtained

assumingavalueof~0.3GeV/cm3forthelocalDMdensityintheMilkyWayhalo(Barnab-Heideretal.2005;Lewin&Smith1996;Gates,Gyuk,&Turner1995).

WIMP-nucleoninteractionsintheSun(Press&Spergel1985;Silk,Olive,&Srednicki1985)orintheEarth(Freese1986;Gaisser,Steigman,&Tilav1986;Krauss,Srednicki,&Wilczek1986;Belotsky,Damour&Khlopov2002)wouldcausetheWIMPstoloseenoughkineticenergytobecometrappedintheirrespectivepotentialwells,whichcouldinturncreateanobservableneutrino uxfromDMannihila-tioninthecore.However,similartodirectdetectionexper-iments,nosuchneutrinosignalhasbeenobserved.Acrucialfactortoconsiderinlightofthesenullre-sultsistheirregularitiesinthedistributionofDMinthehalo.Density uctuationsonsub-parsecscalesallowforthepossibilityforoursolarsystemtoresideinaregionofsig-ni cantlylowerdensitythantheaverage(Taylor&Babul2005).Ifthisisthecase,thentheactualWIMP-nucleon

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