Light dark matter

In astronomy and cosmology, light dark matter is dark matter weakly interacting massive particle (WIMP) candidates with masses less than 1 GeV. These particles are heavier than warm dark matter and hot dark matter, but are lighter than the traditional forms of cold dark matter. The Lee-Weinberg bound limits the mass of the favored dark matter candidate, WIMPs, that interact via the weak interaction to ${\displaystyle \approx 2}$ GeV. This bound arises as follows. The lower the mass of WIMPs is, the lower the annihilation cross section, which is of the order ${\displaystyle \approx m^{2}/M^{4}}$, where m is the WIMP mass and M the mass of the Z-boson. This means that low mass WIMPs, which would be abundantly produced in the early universe, freeze out (i.e. stop interacting) much earlier and thus at a higher temperature, than higher mass WIMPs. This leads to a higher relic WIMP density. If the mass is lower than ${\displaystyle \sim 2}$ GeV the WIMP relic density would overclose the universe.

...
Wikipedia