简介:Inthescenariowherethedarkmatter(DM)particlesχχˉpairannihilatethrougharesonanceparticleR,theconstraintfromDMrelicdensitymakesthecorrespondingcrosssectionforDM-nucleielasticscatteringextremelysmall,andcanbebelowtheneutrinobackgroundinducedbythecoherentneutrino-nucleiscattering,whichmakestheDMparticlebeyondthereachoftheconventionalDMdirectdetectionexperiments.WepresentanimprovedanalyticalcalculationoftheDMrelicdensityinthecaseofresonantDMannihilationfors-andp-wavecasesandinvesitgatetheconditionfortheDM-nucleiscatteringcrosssectiontobeabovetheneutrinobackground.WeshowthatinHiggs-portaltypemodels,forDMparticleswiths-waveannihilation,thespin-independentDM-nucleusscatteringcrosssectionisproportionaltoΓR/mR,theratioofthedecaywidthandthemassofR.ForatypicalDMparticlemass~50GeV,theconditionleadstoΓR/mR≥O(10-4).Inp-waveannihilationcase,thespin-independentscatteringcrosssectionisinsensitivetoΓR/mR,andisalwaysabovetheneutrinobackground,aslongastheDMparticleislighterthanthetopquark.TherealsingletDMmodelisdiscussedasaconcreteexample.
简介:ByusingthegeneralizedDebyediffractionintegral,thispaperstudiesthespatialcorrelationpropertiesandphasesingularityannihilationofaperturedGaussianSchell-model(GSM)beamsinthefocalregion.Itisshownthatthewidthofthespectraldegreeofcoherencecanbelarger,lessthanorequaltothecorrespondingwidthofspectraldensity,whichdependsnotonlyonthescalarcoherencelengthofthebeams,butalsoonthetruncationparameter.Withagradualincreaseofthetruncationparameter,apairofphasesingularitiesofthespectraldegreeofcoherenceinthefocalplaneapproacheseachother,resultinginsubwavelengthstructures.Finally,theannihilationofpairsofphasesingularitiestakesplaceatacertainvalueofthetruncationparameter.Withincreasingscalarcoherencelength,theannihilationoccursatthelargertruncationparameter.However,thecreationprocessofphasesingularitiesoutsidethefocalplaneisnotfoundforGSMbeams.
简介:PositronannihilationtechniquewasusedtostudythemicellebehaviorsoftwoSBStriblockcopolymersinMEKsolventatdifferenttemperatures.Annihilationlifetimeτ3ofortho-positronium(o-Ps)exhibitedanobvioustransitionfromshorterlifetimetolongerlifetimewithtemperature.ItwasattributedtothechangeofmicellebehaviorofSBScopolymermoleculesinthesolution.Experimentalresultsofsedimentationvelocityofultracentrifugewerealsoreported.