Spin degeneracy in multi-hadron systems with a heavy quark

We study multi-hadron systems with a single heavy quark (charm or bottom) in the limit of heavy quark mass. The spin degeneracy of the states with quantum numbers $(j+1\mathrm{/}2{)}^P$ and $(j-1\mathrm{/}2{)}^P$ for $j\mathrm{\ne }0$, known in a normal hadron, can be generalized to multi-hadron systems. The spin degeneracy is the universal phenomena for any multi-hadron systems with a single heavy quark, irrespective of their internal structures, including compact multi-quarks, hadronic molecules and exotic nuclei. We demonstrate the spin degeneracy in the hadronic systems formed by a heavy hadron effective theory; $P^{(\ast )}N$ states with a $P^{(\ast )}={\bar{D}}^{(\ast )}$, $B^{(\ast )}$ meson and a nucleon $N$, and a $P^{(\ast )}$ meson in nuclear matter.