Study of FCNC mediated Z boson effect in the semileptonic rare baryonic decays Λb → Λl+ l-

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We study the effect of the FCNC mediated Z boson in the rare semileptonic baryonic decays Λb → Λl+ l-. We consider the model where the standard model fermion sector is extended by an extra vector like down quark, as a consequence of which it allows CP violating Z mediated flavor changing neutral current at the tree level. We find that due to this non-universal Zbs coupling, branching ratios of the rare semileptonic Λb decays are enhanced reasonably from their corresponding standard model values and the zero point of the forward backward asymmetry for Λb → Λμ+ μ- is shifted to the left.