Dark matter halos with cores from hierarchical structure formation

We show that dark matter emerging from late decays ($z\lesssim 1000$) produces a linear power spectrum identical to that of cold dark matter (CDM) on all observationally relevant scales ($\gtrsim 0.1\mathrm{Mpc}$), and simultaneously generates observable constant-density cores in small dark matter halos. We refer to this class of models as meta-cold dark matter ($m\mathrm{CDM}$), because it is born with nonrelativistic velocities from the decays of cold thermal relics. The constant-density cores are a result of the low phase-space density of $m\mathrm{CDM}$ at birth. Warm dark matter cannot produce similar size phase-space limited cores without saturating the $\mathrm{Ly}\alpha$ power spectrum bounds. Dark matter-dominated galaxy rotation curves and stellar velocity dispersion profiles may provide the best means to discriminate between $m\mathrm{CDM}$ and CDM. $m\mathrm{CDM}$ candidates are motivated by the particle spectrum of supersymmetric and extra dimensional extensions to the standard model of particle physics.