Flavour structure , flavour symmetry and supersymmetry ∗

One of the most obscure sides of particle physics concerns the fermion flavor structure. This is a complex problem with different aspects questioning the origin of the mass spectrum and mixing pattern of quarks and leptons (including neutrinos) and CP-violation, as well as the suppression of flavor changing (FC) neutral currents, the strong CP-problem, etc. [1]. Presently, thanks to the new data from the atmospheric and solar neutrino experiments, the flavor problem is getting more intriguing. On the one hand, the experimental data hint to a hierarchical neutrino mass spectrum, similarly to the case of the charged leptons and quarks. On the other hand, the lepton mixing pattern strongly differs from that of the quarks. In particular, the 2-3 lepton mixing angle is nearly maximal, θ 23 ≃ 45 ◦ in contrast with the analogous quark mixing angle, θ 23 ≃ 2 . The concept of supersymmetry per se does not help in understanding the fermion flavor structure, and in addition it creates another problem, the so called supersymmetric flavor problem, related to the sfermion mass and mixing pattern. In the MSSM the fermion sector consists of chiral superfields containing the quark and lep-