Implications of Milky Way Substructures for the Nature of Dark Matter
  We study how the indirect observation of dark matter substructures in the
Milky Way, using recent stellar stream studies, translates into constraints for
different dark matter models. Particularly, we use the measured number of dark
subhalos in the mass range $10^7-10^9\,{\rm M_{\odot}}$ to constrain
modifications of the subhalo mass function compared to the cold dark matter
scenario. We obtain the lower bounds $m_{\rm WDM} > 3.2\,{\rm keV}$ and $m_{\rm
FDM} > 5.2\times 10^{-21}\,{\rm eV}$ on the warm dark matter and fuzzy dark
matter particle mass, respectively. When dark matter is coupled to a dark
radiation bath, we find that kinetic decoupling must take place at temperatures
higher than $T_{\rm kd} > 0.7\,{\rm keV}$. We also discuss future prospects of
stellar stream observations.
