We study strong and radiative decays of excited singly heavy baryons (SHBs) using an effective chiral Lagrangian based on the diquark picture proposed in Ref. [1]. The effective Lagrangian contains a $U_A (1)$ anomaly term, which induces an inverse mass ordering between strange and non-strange SHBs with spin-parity $1/2^-$. We find that the effect of the $U_A (1)$ anomaly combined with flavor-symmetry breaking modifies the Goldberger-Treiman relation for the mass difference between the ground state $Lambda_Q (1/2^+)$ and its chiral partner $Lambda_Q (1/2^-)$, and $Lambda_Q (1/2^-) Lambda_Q (1/2^+) eta$ coupling, which results in suppression of the decay width of $Lambda_Q (1/2^-) to Lambda_Q (1/2^+) eta$. We also investigate the other various decays such as $Lambda_Q (1/2^-) to Sigma_Q (1/2^+, , 3/2^+) pi pi$, $Lambda_Q (1/2^-) to Sigma_Q (1/2^+) pi$, $Lambda_Q (1/2^-) to Sigma_Q (1/2^+, , 3/2^+) gamma$, and $Lambda_Q (1/2^-) to Lambda_Q (1/2^+) pi^0$ for wide range of mass of $Lambda_Q (1/2^-)$.
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