Bounds on fourth generation induced Lepton Flavour Violating double insertions in Supersymmetry

We derive bounds on leptonic double mass insertions of the type ${\delta }_{i4}^l{\delta }_{4j}^l$ in four generational MSSM, using the present limits on $l_i\to l_j+\gamma$. Two main features distinguish the rates of these processes in MSSM4 from MSSM3 : (a) tan$\beta$ is restricted to be very small $\lesssim 3$ and (b) the large masses for the fourth generation leptons. In spite of small $\tan \beta$, there is an enhancement in amplitudes with $llrr$(${\delta }_{i4}^{ll}{\delta }_{4j}^{rr}$) type insertions which pick up the mass of the fourth generation lepton, $m_{{\tau }^{\mathrm{\prime }}}$. We find these bounds to be at least two orders of magnitude more stringent than those in MSSM3.