Exclusive Rare Decays of Heavy Baryons to Light Baryons: $\Lambda_b \ri   ghtarrow \Lambda \gamma$ and $\Lambda_b \to \Lambda l^{+} l^{-}$
  Rare decays $\Lambda_b \to \Lambda \gamma$ and $\Lambda_b \to \Lambda l^{+} l^{-}$ (l= e, $\mu$) are examined. We use QCD sum rules to calculate the hadronic matrix elements governing the decays. The $\Lambda$ polarization in the decays is analyzed and it is shown that the polarization parameter in $\Lambda_b \to \Lambda \gamma$ does not depends on the values of hadronic form factors. And the energy spectrum of $\Lambda$ in $\Lambda_b \to \Lambda l^{+} l^{-}$ is given. 
Chao-Shang Huang and Hua-Gang Yan