Can lepton flavor violating interactions explain the atmosph(5)

We investigate whether flavor changing neutrino interactions (FCNIs) can be sufficiently large to provide a viable solution to the atmospheric neutrino problem. Effective operators induced by heavy boson exchange that allow for flavor changing neutrino sca

InordertoobtainacompletelistoftheseoperatorswenotethatLorentzinvarianceimpliesthatanyfermionicbilinearBijcancoupletoeitherascalar(S)oravector(V)boson.Ifthetwofermionsofthebilinearhavethesame(opposite)chiralitytheyrequirescalar(vector)couplings.Toformagaugeinvarianttrilinearcoupling,thebosonBmusthaveoppositehyperchargeYandtransformintheappropriaterepresentationofSU(2)LandSU(3)C.SincetheSMneutrinosonlyappearindoubletsofSU(2)Landsinceallright-handed(left-handed)chargedfermionstransformasSU(2)Lsinglets(doublets),itfollowsthatanybosonBthatcouplestothefermionicbilinearcanonlybeasinglet(s),adoublet(d)oratriplet(t)ofSU(2)L.AllrelevantbilinearscontainingonlyleptonsarelistedinTab.1,andthosethatarebuiltfromaleptondoubletandaquarkarelistedinTab.2.InTab.3we¯.HereQandLdenotelisttherelevantdiquarkbilinears,namely,thosethatcancoupletoLL

theleft-handedSMquarkandleptondoublets,andeR,uR,dRrefertotheright-handedSMsinglets.Someofthesecouplingsappearinwellknownextensionsofthestandardmodel.Forexample,insupersymmetricmodelswithoutR-parity(SUSYRp)[22],fermionbilinears c),left-handedsquarks(Q c),right-handedsleptons( c)cancoupletoleft-handedsleptons(LR c),asindicatedinthethirdcolumnofthetables.Anandright-handeddownsquarks(dR

exampleforascalartripletisthe Linleft-rightsymmetricmodels(LRSMs)[23].

IngeneralanytwobilinearsappearinginTab.1–3thatcoupletothesamebosoncanbecombinedtoafourfermioninteractionwithe ectivecouplingasgiveninEq.(2.1).In

′for ordertogenerateanon-zero fνinEq.(2.2)atleastoneofthebilinearshastocontainν

aleptondoubletL.Clearly,fourfermionoperatorsthataretheproductofonebilinearanditshermitianconjugatecanbeconstructed.Ifthetwobilinearshavethesame(di erent) avorstructuretheresultingoperatorwillconserve(violate)lepton avor.Inaddition,the¯)bilinearcancoupleto((LL¯)(QQ¯),(LL¯)(eReR),(LLdRdR).Notethatscalarorvector eldsthattransformidenticallyundertheunbrokenSU(3)C U(1)EMsymmetrycanmix.Ifthismixingisbetweenadoubletandasingletoratriplettheresultingoperatorsviolatetotalleptonnumberandarenotrelevantforouranalysis.Inthecaseofsinglet–tripletmixingnonewoperatorsaregenerated.Thereforethiskindofmixingdoesnota ectourconclusionsandweneglectit.

TodemonstratehowSU(2)Lrelatedprocessescanbeusedtoconstraintheparameters′f¯ fνor ν,letusconsiderforexamplethebilinearLfR(f=e,u,d)thatcouplesviaascalardoublettoitshermitianconjugate

λ αfλβf

2M1(

(fRνβ)+ αfR)(λ αfλβf αγµ β)(22M1fRγµfR)

andM1,2LαfRtothescalardoubletdenotethemassesofitsSU(2)Lcomponents.Theimportantpointisthatthe