Aug. 16, 2003 Mitsuru Kakizaki 1

Democratic (s)fermions andlepton flavor violation

Mitsuru Kakizaki 　（ Tohoku Univ. ）　　　　　　　　　　　　　　　　　

Aug. 16, 2003Ref.: K. Hamaguchi, M. K. and Masahiro Yamaguchi, to appear in PRD, hep-ph/0212172

Proposal of a new alignment mechanism based on the democratic mass matrices

Comparison between alignment and the conventional mSUGRA

Aug. 16, 2003 Mitsuru Kakizaki 2

１． MotivationTwo severe flavor problems in SUSY

modelsThe flavor problem of fermion masses The charged fermion mass hierarchy Small quark mixing but bi-large lepton mixing

The flavor problem of sfermion masses Generic flavor mixing among sfermions Large FCNC

In order to be consistent with experiments

Aug. 16, 2003 Mitsuru Kakizaki 3

Attempts to solve SUSY flavor problem

Degeneracy: Decoupling: Alignment: Idea: A high energy theory which controls flavor

FCNC suppression Fermion masses and mixings Measurement of FC processes and sfermion mass spectra We can find the fermion mass generation mechanism

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Purposes of this talk

Proposal of a new alignment mechanism based on the democratic mass matrices

Comparison between alignment and the conventional mSUGRA Sfermion masses Flavor changing processes

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2. Democratic mass matrix

Idea: equality of three generations The permutation group on 3 objects:

: a 3 reducible representation　　　　　　　　　　　　　　　　 The third

generation: 3 = 1 + 2 The light

generations:

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The charged lepton mass matrix

sym. The democratic matrix:

The unique invariant Small breaking

The mass hierarchy: Bi-large unitary matrices:

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The neutrino mass matrix We consider majorana neutrinos:

sym. 　 Universal Democrat

ic We assume absence of the democratic part:

Degenerate neutrinos Bi-large mixing and small Ue3

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3. Democratic sfermions Idea: Interactions between the MSSM fields a

nd hidden fields also obey the democracy Soft scalar mass matrices: 　　

In the fermion mass basis,

Non-universal masses but small flavor mixing

　　 Alignment

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Slepton masses Left-handed slepton masses

Bi-large neutrino mixing requires absence of the democratic part of the Kahler potential for

No LFV

Right-handed slepton masses Small flavor mixing LFV

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The present experimental bound (MEGA (1999)):

Future sensitivity (PSI) :

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Degeneracy vs alignment MSSM + (mSUGRA + RG effects) Collider experiments:

LFV searches:

Democratic ansatz

Searches with polarized muons are promising

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4. Summary An interesting solution for the SUSY flavor

problem The mechanism which controls fermion mass

structure also dictates FCNC suppression Predictions in the democratic approach

Observable

We can distinguish models of flavor by collider experiments and LFV searches

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Problems

What is the origin of the democratic matrices? Symmetry Geometry

What is the origin of the small S3 breaking parameters?

Why is the democratic part absent for ?