Manifesting hidden dynamics of a sub-component dark matter

We emphasize the distinctive cosmological dynamics in multi-component dark-matter scenarios and their impact on probing a sub-dominant component of dark matter. The dynamics originate from the conversion among different dark-matter components. We find that the temperature of the self-interacting sub-component dark matter is significantly enhanced by the dark-matter annihilation into the sub-component. The same annihilation sharply increases the required annihilation cross section for the sub-component as we consider a smaller relative abundance fraction among the dark-matter species. Because of the enhanced temperature and couplings of the sub-component, contrary to a naive expectation, the sub-component with smaller abundance fractions tends to be disfavored by dark-matter direct/indirect-detection experiments and cosmological observations. We demonstrate this by taking a dark photon portal scenario for the sub-component at the sub-GeV mass scale. For the abundance fraction ≳ 10 %, the enhanced temperature of the sub-component is subject to warm dark matter constraints which are complementary to the parameter space probed by accelerator-based experiments. Smaller abundance fractions tend to be disfavored by accelerator-based experiments due to the enhanced coupling to Standard Model particles.