The rare decays of $\Lambda_b$ baryon governed by the quark level transitions $ b \to s$, are investigated in the fourth quark generation model popularly known as SM4. Recently it has been shown that SM4, which is a very simple extension of the standard model, can successfully explain several anomalies observed in the CP violation parameters of $B$ and $B_s$ mesons. We find that in this model due to the additional contributions coming from the heavy $t'$ quark in the loop, the branching ratios and other observables in rare $\Lambda_b$ decays deviate significantly from their SM values. Some of these modes are within the reach of LHCb experiment and search for such channels are strongly argued.

Comment: 19 pages, 7 figures, typos corrected, published version