V. SUPERSYMMETRY Supersymmetric models provide, in general, new sources of flavor violation, for both the quark and the lepton sectors. The main new sources are the supersymmetry breaking soft mass terms for squarks and sleptons, and the trilinear couplings of a Higgs field with a squark-antisquark, or slepton-antislepton pairs. Let us focus on the squark sector. The new sources of flavor violation are most commonly analyzed in the basis in which the corresponding (down or up) quark mass matrix and the neutral gaugino vertices are diagonal. In this basis, the squark masses are not necessarily flavor-diagonal, and have the form where M, N = L, R label chirality, and i, j, k, l = 1 , 2 , 3 are generation indices. ( M 2 ˜ $_{q}$)$_{L}$ and ( M 2 ˜ $_{q}$)$_{R}$ are the supersymmetry-breaking squark masses-squared. The A q parameters enter in the trilinear scalar couplings A q $^{$_{ij}$φ$_{q}$}$˜ $^{q$_{Li}$}$˜ q ∗ $_{Rj}$, where φ$_{q}$ ( q = u, d ) is the q -type Higgs boson and v$_{q}$ = 〈 φ$_{q}$ 〉 . In this basis, flavor violation takes place through one or more squark mass insertion. Each mass In this basis, flavor violation takes place through one or more squark mass insertion. Each mass insertion brings with it a factor of ( δ q $_{ij}$)$_{MN}$ ≡ ( M 2 ˜ $_{q}$) MN ij / ˜ m 2 $_{q}$, where ˜ m 2 q is a representative q -squark mass scale. Physical processes therefore constrain For example, Note that the contributions with two or more insertions may be less suppressed than those with only one. In terms of mass basis parameters, the ( δ q $_{ij}$)$_{MM}$ ’s stand for a combination of mass splittings and mixing angles: where K q M is the mixing matrix in the coupling of the gluino (and similarly for the bino and neutral wino) to q$_{Li}$ − ˜ q$_{Mα}$ ; ˜ m 2 q = 1 3 ∑ 3 α =1 ˜ m 2 q$_{Mα}$ is the average squark mass-squared, and Δ ˜ m 2 q$_{α}$ = ˜ m 2 q$_{α}$ − ˜ m 2 $_{q}$. Things simplify considerably when the two following conditions are satisfied [42], which means that a two generation effective framework can be used (for simplicity, we omit here the chirality index): 18 ( δ q $_{ij}$)$_{MM}$ = 1 ˜ m 2 q ∑ α ( K q $_{M}$)$_{iα}$ ( K q $_{M}$) ∗ $_{jα}$Δ ˜ m 2 $_{q$_{α}$}$, (5.4) [( δ d $_{12}$)$_{LR}$ ]$_{eff}$ ∼ max[ A d $_{12}$v$_{d}$ / ˜ m 2 $_{d}$, ( M 2 ˜ $_{d}$)$_{L}$$_{1}$$_{k}$ A d k $_{2}$v$_{d}$ / ˜ m 4 $_{d}$, A d 1 $_{k}$v$_{d}$ ( M 2 ˜ $_{d}$)$_{Rk}$$_{2}$ / ˜ m 4 $_{d}$, . . . , (1 ↔ 2)] . (5.3) [( δ q $_{ij}$)$_{MN}$ ]$_{eff}$ ∼ max[( δ q $_{ij}$)$_{MN}$ , ( δ q $_{ik}$)$_{MP}$ ( δ q $_{kj}$)$_{PN}$ , . . . , ( i ↔ j )] . (5.2) ˜ q ∗ $_{Mi}$( M 2 ˜ $_{q}$) MN ij ˜ q$_{Nj}$ = (˜ q ∗ Li ˜ q ∗ $_{Rk}$)   ( M 2 ˜ $_{q}$)$_{Lij}$ A q $_{il}$v$_{q}$ A q $_{jk}$v$_{q}$ ( M 2 ˜ $_{q}$)$_{Rkl}$     ˜ q$_{Lj}$ ˜ q$_{Rl}$   , (5.1)