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

fscalardoubletexchangenotonlygivesrisetothefour-FermioperatorOνin(1.2)(with(V A) (V+A)structure),butalsoproducestheSU(2)Lrelatedoperator

fO ≡(

2M2.(2.5)

Constructingalltherelevantfourfermionoperatorsthatareinducedbythecouplings

fbetweenthebilinearslistedinTab.1–3,one ndsthatingeneralO isgeneratedtogether

f′withOν.Heref′canbedi erentfromfonlyforinteractionswithquarks,thatisinsomeudduecasesO (O )isgeneratedtogetherwithOν(Oν).TheleptonicoperatorO isalways

egeneratedtogetherwithOνunlesstheinteractionismediatedbyanintermediatescalar

SU(2)Lsingletthatcouplesto

(LαLe)s=1(2 cανe),(2.6)

where α=µL,τLforα=µ,τ,withtheelementarycouplingλαe.Thecouplingof(LαLe)sto(LβLe) sthatismediatedbyascalarsingletofmassMyieldsthee ectiveinteractionsλ βeλαe

ceLνβ)(ceLνβ)(νe cβ)(

νβγµ α)+(νe cβ)( βγµ α) ( βγµνα),

(2.8) 2M2(νβγµνα) (

whereweusedaFierztransformationandtheidentityBγµAtoobtain(2.8).

eOnecanseethatinthiscaseOνisgeneratedtogetherwiththreemoreoperatorsthathave

thesamee ectivecoupling(uptoasign).However,unlikeforthecaseofintermediatedoubletsortriplets,alltheseoperatorsinvolvetwochargedleptonsandtwoneutrinos.

B.Experimentalconstraints

fThereisnoexperimentalevidenceforanynon-vanishingGfµτ.Therefore,wheneverO

fisgeneratedtogetherwithOν,onecanusetheupperboundsonGfµτtoderiveconstraints

e onGf→νµντ.ThemoststringentconstraintonGµτisduetotheupperboundonτ

µ e+e [24,25]:

BR(τ →µ e+e )<1.7×10 6.

(2.9)