Can lepton flavor violating interactions explain the atmosph(3)

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

ariseswhenextendingthefermionicsectorofthestandardmodelandisduetoZ-induced avor-changingneutralcurrents(FCNCs)[17,18].Recentanalyses[6–8]ofnon-standardneutrinointeractionsasapossiblesolutiontotheatmosphericneutrinodatasuggestthatFCNIscanprovideagood ttothedataprovidedthat

′q>e′e> q, 0.1or νν～ν, ν～0.3.(1.3)

InRef.[6–8]onlynewinteractionsinvolvingthedquarkwereconsidered.Sincetheearthiselectricallyneutralanditsneutrontoprotonratioisclosetounity,weconcludethatthe

′qe′erequiredvaluesfor qand aresimilarforq=d,u,whilethosefor and ννννarelargerby

afactorofthree.

TheauthorsofRef.[19,20]arguethatsuchascenariodoesnotleadtoagooddescriptionofthedata.Inthispaperwedonottrytoresolvethisissue,butinvestigatewhetherthe

′flowerboundson fνand νin(1.3)areatallphenomenologicallyviable.Theauthorsof<Ref.[8]haveestimatedtheupperbound dν～0.1 1.0fromthelowenergyνµneutral

currentcross-section,concludingthatFCNIscouldberelevantfortheANanomaly.In

′fRef.[21]speci cmodelsthatcouldgive fνand νaslargeasin(1.3)werediscussed.We

argue,however,thatmodel-independentlytheupperboundsfromrelated,chargedlepton

′fdecaydataimplythat fνor νcanbeatmostattheone-percentlevel.Thusweconclude

thatFCNIsdonotplayasigni cantrolefortheatmosphericneutrinoproblem.

InSectionIIweinvestigateinamodel-independentframeworktheconstraintsonFCNIsthatareinducedbyheavybosonexchange.Inmostcasestheupperboundsonlepton avorviolatingtaudecays,inparticularτ →µ M(M=π0,ρ0,η)andτ →µ e+e ,implystringentconstraintson fνthatareinconsistentwith(1.3).Intheremainingcasessevereconstraintson ′fνarederivedusingboundsonleptonuniversalityviolation.InSectionIIIweshowthatalsoZ-inducedFCNCs,thatariseduetoheavysingletneutrinos,cannotbelargeenoughtoexplaintheANanomaly.WeconcludeinSectionIV.

II.FLAVORCHANGINGNEUTRINOINTERACTIONSINDUCEDBYHEAVY

BOSONEXCHANGE

A.Formalism

TheanalysisofFCNIsthatcouldberelevantfortheANproblemissimilartothediscussioninRef.[13],wherethepossibilitythatFCNIsexplaintheLSNDresults[11]wasruledout.Ingeneral,thepresenceofaheavybosonBthatcouplestofermionbilinearsBijwiththetrilinearcouplingsλij,wherei,j=1,2,3refertofermiongenerations,givesriseto

Bklwiththee ectivecouplingthefourfermionoperatorBij

B BGN=λ ijλkl

22MB,(2.1)