Suppression of decay widths in singly heavy baryons induced by the U_A (1) anomaly

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 $\Lambda_Q (1/2^-)$.