Divisors on complete multigraphs and Donaldson-Thomas invariants of loop quivers

We study the action of $S_n$ on the set of break divisors on complete multigraphs $K_n^m$. We provide an alternative characterization for these divisors, by virtue of which we show that orbits of this action are enumerated by the numerical Donaldson-Thomas invariants of $(m+1)$-loop quivers. Our characterization also allows us to restrict this action to $S_{n-1}$ and we identify the resulting $S_{n-1}$-module as that afforded by $K_n^m$-parking functions.