  We construct an effective hadronic model including $\Lambda_c(2595)$,
$\Lambda_c(2625)$, $\Lambda_b(5912)$ and $\Lambda_b(5920)$ regarding them as
chiral partners to $\Sigma_c(2455)$, $\Sigma_c(2520)$, $\Sigma_b$ and
$\Sigma_b^\ast$, respectively, with respecting the chiral symmetry and
heavy-quark spin-flavor symmetry. We determine the model parameters from the
experimental data for relevant masses and decay widths of $\Sigma_c^{(\ast)}$
and $\Lambda_c(2595)$. Then, we study the decay widths of $\Lambda_c(2625)$,
$\Lambda_b(5912)$ and $\Lambda_b(5920)$. We find that, although the decay of
$\Lambda_c(2595)$ is dominated by the resonant contribution through
$\Sigma_c(2455)$, non-resonant contributions are important for
$\Lambda_c(2625)$, $\Lambda_b(5912)$ and $\Lambda_b(5920)$, which reflects the
chiral partner structure. We also study the radiative decays of the baryons,
and show that each of their widths is determined from the radiative decay width
of their chiral partners.
