Lepton flavour violation (tau decays) A.Ilakovac, Dept. of Physics, Faculty of Science, U. of Zagreb, Croatia

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Lepton flavour violation (tau decays)A.Ilakovac,
Dept. of Physics, Faculty of Science, U. of
Zagreb, Croatia
CONTENT Standard model does not permit LFV Most
common introduction of neutrino masses Sources of
LFV/LNV Model-independent (operator) analysis of
LFV with SM fields LFV mechanisms Connecting LFV
with neutrino parameters Examples of
interrelations between processes Hadronic part of
LFV amplitudes Some results for tau-lepton
processes Conclusions
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A. Ilakovac, U. of Zagreb, Novosibirsk, February
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A. Ilakovac, U. of Zagreb, Novosibirsk, February
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• Two approaches to determine see-saw parameters
• top-down start with a specific model (GUT,
  Froggatt-Nielsen, strings,) and compare the
  predictions with the experiments, many different
  possibilities
• 2. bottom-up exploit all the information
  available at low energies on the leptonic sector
  in order to resconstruct the high-energy theory
  completely phenomenological, very difficult in
  practice
• A. Ibarra impossible in SMv possible in
  MSSM

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2. LFV and LFC
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• Hadronic part of LFV amplitudes
• tau-lepton is heavy enough to decay into hadrons
  LFV with hadrons in the final state possible
• - simplest hadronization methods
• (a) PCAC axial vector
• (b) VMD vector
• (c) chiral perturbation theory scalar and
• pseudoscalar (e.o.m. for current quark
  masses
• gives similar results)
• (d) tensor e.o.m. for current quark masses
  and (b)

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M.J. Herrero, hep-ph/0510405
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P. Paradisi, Flavour in the era of the LHC, CERN,
February 2006
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CONCLUSIONS 1.Lepton flavour violation must
occur at some level. 2. Discovery of any of LFV
processes, except neutrino oscillations would
give important information on the structure of
theory. 3. LFV processes have to be always
analyzed taking into account information of all
other LFV and LFC processes. 4.Many theoretical
models are not completely explored, and in
specific regions of parameter space give results
comparable to the present experimental limits for
BRs of neutrinoless LFV processes. For some SUSY
models large regions of parameter space are
excluded by LFV experimental data. In this
context tau-lepton LFV data play important role.
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SM parameters
m
LFV processes
MSSM
MSSM
MR
RGE
SO(10) structure
MD, MR