Model independent analysis of MeV scale dark matter. II. Implications from e- e+ colliders and direct detection

Dark matter particles with masses in the sub-giga electron volt range have escaped severe constraints from direct detection experiments such as LUX, PANDAX-II, and XENON100, as the corresponding recoil energies are, largely, lower than the detector thresholds. In a companion paper, we demonstrated, in a model independent approach, that a significantly large fraction of the parameter space escapes the cosmological and astrophysical constraints. We show here, though, that the remaining parameter space lends itself to the possibility of discovery at both direct detection experiments (such as CRESST-II) as well as in a low-energy collider such as Belle-II. In examining the popular gamma + phi phi* channel, we employ refined techniques that successfully overcome the detector lacunae to reach very high sensitivities. Furthermore, the l(-)l(+) + phi phi* channel is, for the first time, shown to have comparable or even higher sensitivity.