Lepton Flavor Violation

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Lepton Flavor Violation

• Yasuhiro Okada (KEK)
• October 7, 2005
• 3rd 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
  flavor 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
m-e conversion search at 0(10-18) will
be possible in a future experiment at J-PARC
(PRIME)
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Various observables in mu LFV processes
Angular distribution in polarized muon LFV
processes
m-gt eg
Two P-odd and one T-odd asymmetries
Example A -1 for the SUSY seesaw model
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Z dependence of mu-e conversion processes.
Z-dependence can distinguish different
LFV Interactions.
R.Kitano, M.Koike and Y.O. 2002
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Tau LFV processes
Various 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
Super KEKB LoI
ee- B factory
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Polarized tau decay
R.Kitano and Y.O. 2001
Using angular correlation of tau decay products
in signal and opposite sides, asymmetries of
polarized tau decay are obtained.
A-1 case
Example
Similarly, two P-odd and one T-odd asymmetries
can be defined for tau -gt lll decays.
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m LFV in SUSY models
In many models of SUSY, off-diagonal terms of the
slepton mass matrixes are induced from
Interaction at GUT /seesaw neutrino scales.
F.Borzumati, A.Masiero 1986
In many cases, LFV processes are dominated by the
m-gte g amplitude.
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Enhancement due to Higgs exchange contribution at
large tan b case
Higgs exchange diagram have a ( tan b )6
contribution. We have shown 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.
R.Kitano and Y.O.
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
RR
LL
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LR
RL
Higgs exchange effect is evident for the LL case.
Situation is more complicated in the RR case due
to possible cancellation in both m -gt eg and m-e
conversion amplitudes. Higgs exchange effects are
seen in LR/RL cases.
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m/t LFV in LR symmetric model
A.Akeroyd, M.Aoki, Y.O.
(Non-SUSY) left-right symmetric model
V.Cirigliano, A.Kurylov, M.J.Ramsey-Musolf,
P.Vogel, 2004 O.M.Boyarkin, G.G.Boyarkina,
T.I.Bakanova, 2004
Llt-gtR parity
Higgs fields, (bi-doublet, two triplets)
Low energy (TeV region ) seesaw mechanism for
neutrino masses
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Four lepton interactions are dominant among
various LFV processes.
In general,
We consider following questions Which is
important, m-gt3e or t -gtlll ? What are sizes of
various tau decay modes? What is the asymmetry of
the tau LFV decay?
Heavy particles at the TeV region
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Relationship between tau and mu decays depends on
heavy neutrino Masses. Hierarchical heavy
neutrino masses -gt large tau decay processes
Blue MR3 can be much Heavier than MR1
and MR2. Pink nearly degenerate Heavy neutrinos
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Case 2
Case 1
Dominant modes depend on flavor mixings in the
heavy neutrino sector.
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Independent of LFV decay modes including m-gt 3e.

• Summary
• Tau vs. mu
• heavy neutrino mass hierarchy
• (2) Various tau modes
• flavor mixing in heavy neutrino sector
• (3) t -gt3l (or m -gt 3e) asymmetry
• ratio of the left and right doubly charged
  Higgs boson masses.

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Summary

• Experimental Improvement is expected in coming
  years for m -gt eg (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.