by m$_{2}$/M$_{2}$ . On the other hand, the χ$_{L}$ → E$_{R}$φ transitions are SU (2)-conserving, and therefore proportional to m$_{2}$/v which, by assumption, is of order one. To proceed we note that the rotation from the interaction basis to the mass basis involves small rotation angles. We can therefore extract the leading flavor structure by analyzing the flavor eigenstates. The χ$_{L}$ → E$_{R}$ transitions depend on ( m$_{2}$/v ) Y $^{χ}$. Examining Table I, we learn that in models LE and LL it will be flavor-suppressed as Y $^{E}$, while in the EE model, it is unsuppressed by flavor parameters. In any case, the strongest suppression factor that appears in our framework is ( m$_{2}$/v ) y$_{e}$ ∼ 10 − $^{5}$. Thus, the longest-lived lepton can have a decay width of order 10 − 11 its mass, which still gives a lifetime shorter than 10 − 16 seconds. We conclude that all the heavy leptons decay promptly. Among the TeV scale leptons, the shortest-lived has a width of order 1 / (8 π ) of its mass, still too narrow to be measured. We conclude that there is no way to measure the decay width of the heavy vector leptons of our MLFV models in ATLAS/CMS. Finally, we note that the following relation between the various leading decay rates holds to a good approximation: The presence of new SU (2)-doublets and effects of SU (2)-breaking in their spectrum modify the predictions for the electroweak precision measurements and, in particular, the S , T and U parameters [23]. Consider, for example, the T parameter. The shift Δ T due to new contributions is related to the small mass splittings between the neutral and the charged members in the heavy SU (2)-doublets. The mass of the i ’th heavy lepton doublet is of order M$_{2}$X χ i , while the mass splitting is of order ( m$_{2}$Y χ i ) $^{2}$/ ( M$_{2}$X χ i ). (As explained above, MLFV requires that the Y χ and X χ matrices are diagonal.) We thus have 6 Δ T ( χ$_{i}$ ) = O [ ( Δ m$_{χ}$$_{i}$ m$_{Z}$ ) 2 ] ≈ ( m$_{2}$Y χ i ) 4 ( m$_{Z}$M$_{2}$X χ i ) $_{2}$. (2.7) Γ( χ − → hℓ $^{−}$) = 2Γ( χ − → Zℓ $^{−}$) = 2Γ( χ 0 → W $^{+}$ℓ $^{−}$) . (2.6) D. Electroweak precision measurements