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Lepton Flavor Violation

Yasuhiro Okada (KEK)October 7, 20053rd International Conference on Flavor Physics National Central University, Taiwan

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Lepton Flavor Violation in charged lepton processes Charged lepton LFV is a clear evidence of physics

beyond the Standard Model. Neutrino mixing suggests existence of lepton flavo

r mixing. Large LFV in charged lepton processes is possible, if there is new physics at the TeV scale.

There are various processes and observable quantities in muon and tau LFV processes. These are keys to choose a correct model among various candidates.

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Contents of this talk

Phenomenology of muon and tau LFV processes. Two examples

(1) Muon LFV processes in SUSY models including Higgs exchange contributions.

(R.Kitano and Y.O)

(2) Muon and tau LFV processes in the Left-Right symmetric model.

(A.Akeroyd, M.Aoki, and Y.O)

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Three muon LFV processes

-e conversion search at 0(10^{-18}) will bepossible in a future experiment at J-PARC (PRIME)

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Various observables in mu LFV processes

e

Two P-odd and one T-odd asymmetriesExample :A= -1 for the SUSY seesaw model

Angular distribution in polarized muon LFV processes

3e

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Z dependence of mu-e conversion processes.

Z-dependence candistinguish different LFVInteractions.

:dipole

:scalar

:vector

R.Kitano, M.Koike and Y.O. 2002

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Tau LFV processesVarious flavor structures

and their CP conjugates

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Experimental upper bound Y.Miyazaki ESP 2005

Most of processes are bounded by 0(10^-7)

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Future experimental prospects for tau LFV search

e+e- B factory

Super KEKB LoI

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“Polarized” tau decayUsing angular correlation of tau decay products in signal and opposite sides,asymmetries of “polarized” tau decay are obtained. Example:

Similarly, two P-odd and one T-odd asymmetries can be defined for tau -> lll decays.

A=-1 case

R.Kitano and Y.O. 2001

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LFV in SUSY modelsIn many models of SUSY, off-diagonalterms of the slepton mass matrixes are induced from Interaction at GUT /seesaw neutrino scales.

In many cases, LFV processes are dominated by the ->e amplitude.

F.Borzumati, A.Masiero 1986

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Enhancement due to Higgs exchange contribution at large tan case

s s

e

Higgs exchange diagram have a ( tan )^6 contribution. We haveshown impact of this contribution in the SUSY seesaw model (LL case). R.Kitano, M. Koike and S. Komine and Y.O. 2003

Higgs-exchange contribution

Photon-exchange contribution

Dominance of the Higgs exchange affects the Z dependence

dipole, scalar, vector

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Higgs exchange contribution in general case.

LL: 　 Flavor mixing in the left-handed slepton sector (ex. SUSY seesaw model) RR: Flavor mixing in the right-handed slepton sector LR, RL: Flavor mixing in the A term

R.Kitano and Y.O.

LLRR

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Higgs exchange effect is evident for the LL case. Situation is more complicated in the RR case due to possible cancellation in both -> e and-e conversion amplitudes.Higgs exchange effects are seen in LR/RL cases.

LR RL

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LFV in LR symmetric model(Non-SUSY) left-right symmetric model

Higgs fields, (bi-doublet, two triplets)

Low energy (TeV region ) seesaw mechanism for neutrino masses

L<->R parity

V.Cirigliano, A.Kurylov, M.J.Ramsey-Musolf, P.Vogel, 2004O.M.Boyarkin, G.G.Boyarkina, T.I.Bakanova, 2004

A.Akeroyd, M.Aoki, Y.O.

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Four lepton interactions are dominant among various LFV processes.

We consider following questions:Which is important,>3e or ->lll ?What are sizes of various tau decay modes?What is the asymmetry of the tau LFV decay?

Heavy particles at the TeV region

In general,

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Relationship between tau and mu decays depends on heavy neutrinoMasses. Hierarchical heavy neutrino masses -> large tau decay processes

Blue MR3 can be muchHeavier than MR1 andMR2.Pink:nearly degenerateHeavy neutrinos

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Case 1 Case 2

Dominant modes depend on flavor mixings in the heavy neutrino sector.

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Summary

(1) Tau vs. mu : heavy neutrino mass hierarchy(2) Various tau modes: flavor mixing in heavy neutrino sector(3) ->3l (or -> 3e) asymmetry: ratio of the left and right doubly charged

Higgs boson masses.

Independent of LFV decay modesincluding -> 3e.

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Summary

Experimental Improvement is expected in coming years for -> e(MEG) and various tau LFV processes (B factory, LHC).

If there are new particles at the TeV region related to the lepton flavor mixing, the neutrino oscillation can have connection to the charged lepton LFV processes.

There are various observable quantities in muon and tau LFV processes. Different neutrino mass generation mechanism predicts different characteristic signals in LFV processes.