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Leptogenesis as the origin of matter

We explore in some detail the hypothesis that the generation of a primordial lepton-antilepton asymmetry (Leptogenesis) early on in the history of the Universe is the root cause for the origin of matter. After explaining the theoretical conditions for prod

DESY05-031

February2005

LEPTOGENESISASTHEORIGINOFMATTER

arXiv:hep-ph/0502169v2 8 Mar 2006W.Buchm¨ullera,R.D.Pecceib,T.YanagidacaDeutschesElektronen-SynchrotronDESY,22603Hamburg,GermanybDepartmentofPhysicsandAstronomy,UniversityofCaliforniaatLosAngeles,LosAngeles,California,90095,USAcDepartmentofPhysics,UniversityofTokyo,Tokyo113-0033,JapanAbstractWeexploreinsomedetailthehypothesisthatthegenerationofaprimordiallepton-antileptonasymmetry(Leptogenesis)earlyoninthehistoryoftheUniverseistherootcausefortheoriginofmatter.Afterexplainingthetheoreticalconditionsforproducingamatter-antimatterasymmetryintheUniversewedetailhow,throughsphaleronprocesses,itispossibletotransmutealeptonasymmetry–or,moreprecisely,a(B-L)-asymmetry–intoabaryonasymmetry.BecauseLeptogenesisdependsindetailonpropertiesoftheneutrinospectrum,wereviewbrie yexistingexperimentalinformationonneutrinosaswellastheseesawmechanism,whicho ersatheoreticalunderstandingofwhyneutrinosaresolight.Thebulkofthe

reviewisdevotedtoadiscussionofthermalLeptogenesisandweshowthatfortheneutrinospectrumsuggestedbyoscillationexperimentsoneobtainstheobservedvalueforthebaryontophotondensityratiointheUniverse,independentlyofanyinitialboundaryconditions.InthelatterpartofthereviewweconsiderhowwellLeptogenesis tswithparticlephysicsmodelsofdarkmatter.AlthoughaxionicdarkmatterandLeptogenesiscanbeverynaturallylinked,thereisapotentialclashbetweenLeptogenesisandmodelsofsupersymmetricdarkmatterbecausethehightemperatureneededforLeptogenesisleadstoanoverproductionofgravitinos,whichalterthestandardpredictionsofBigBangNucleosynthesis.Thisproblemcanberesolved,butitconstrainsthesupersymmetricspectrumatlowenergiesandthenatureofthelightestsupersymmetricparticle(LSP).Finally,asanillustrationofpossibleotheroptionsfortheoriginofmatter,wediscussthepossibilitythatLeptogenesismayoccurasaresultofnon-thermalprocesses.

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