Astroparticle Physics

278 13 Dark MatterIt is not totally inconceivable that particularly heavyWIMP particles could be represented by primordial blackholes, which could have been formed in the Big Bang be-fore the era of nucleosynthesis. They would provide an idealcandidate for cold dark matter. However, it is very difficult toimagine a mechanism by which such primordial black holescould have been produced in the Big Bang.Recently the Italian–Chinese DAMA 7 collaboration haspublished a result, which could hint at the existence ofWIMPs. Similarly to our Sun, the Milky Way as a wholecould also trap WIMPs gravitationally. During the rotationof the solar system around the galactic center the velocityof the Earth relative to the hypothetical WIMP halo wouldchange depending on the season. In this way the Earth whileorbiting the Sun would encounter different WIMP fluxes dependingon the season. In the month of June the Earth movesagainst the halo (→ large WIMP collision rate) and in Decemberit moves parallel to the halo (→ low WIMP collisionrate).The DAMA collaboration has measured a seasonal vari-ation of the interaction rate in their 100 kg heavy sodiumiodidecrystal. The modulation of the interaction rate withan amplitude of 3% is interpreted as evidence for WIMPs.The results obtained in the Gran Sasso laboratory wouldfavour a WIMP mass of 60 GeV. This claim, however, isin contradiction to the results of an American collaboration(CDMS) 8 , which only observes a seasonal-independentbackground due to neutrons in their highly sensitive lowtemperaturecalorimeter.black holeas WIMP candidategravitational bindingto the Milky Way:possible seasonal-dependentWIMP fluxresults from DAMAand CDMS collaborations13.2.4 Axions“For every complex natural phenomenonthere is a simple, elegant,compelling, but wrong explanation.”Thomas GoldC, P, CP violationWeak interactions not only violate parity P and charge conjugationC, but also the combined symmetry CP. TheCPviolation is impressively demonstrated by the decays of neutralkaons and B mesons. In the framework of quantumchromodynamics (QCD) describing strong interactions, CPviolatingterms also originate in the theory. However, experimentallyCP violation is not observed in strong interactions.7 DAMA – DArk MAtter search8 CDMS – Cryogenic Dark Matter Search