Democratic (s)fermions and lepton flavor violation

1. Democratic (s)fermions andlepton flavor violation Mitsuru Kakizaki　（Tohoku Univ.） Aug. 16, 2003 Ref.: 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 Mitsuru Kakizaki

2. １．Motivation Two severe flavor problems in SUSY models • The flavor problem of fermion masses • The charged fermion mass hierarchy • Small quark mixing but bi-large lepton mixing • The flavor problem of sfermion masses • Genericflavor mixing among sfermions Large FCNC In order to be consistent with experiments 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 Mitsuru Kakizaki

4. 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 Mitsuru Kakizaki

5. 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: Mitsuru Kakizaki

6. The charged lepton mass matrix • sym. The democratic matrix: Theunique invariant Small breaking • The mass hierarchy: • Bi-large unitary matrices: Mitsuru Kakizaki

7. The neutrino mass matrix • We consider majorana neutrinos: sym. Universal Democratic • We assume absence of the democratic part: • Degenerate neutrinos • Bi-large mixing and small Ue3 Mitsuru Kakizaki

8. 3. Democratic sfermions • Idea:Interactions between the MSSM fields and hidden fields also obey the democracy • Soft scalar mass matrices: • In the fermion mass basis, Non-universal masses but small flavor mixing Alignment Mitsuru Kakizaki

9. 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 Mitsuru Kakizaki

10. The present experimental bound (MEGA (1999)): • Future sensitivity (PSI) : Mitsuru Kakizaki

11. MSSM + (mSUGRA + RG effects) Collider experiments: LFV searches: Democratic ansatz Searches with polarized muons are promising Degeneracy vs alignment Mitsuru Kakizaki

12. 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 Mitsuru Kakizaki

13. 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? Mitsuru Kakizaki