The arXiv has a new review of light dark matter direct detection efforts and challenges. Light dark matter, which is maybe a few tens of GeV or less in mass, became a hot topic a few years ago when a number of direct detection experiments started getting results that looked consistent with a light dark matter halo. While the results weren’t necessarily all consistent with one another, people started getting very interested in this idea. Unfortunately, the strongest and most recent limits seem to rule out these possible signals – at least using the standard dark matter halo and interaction models.
The paper talks about recent progress in understanding the possible light dark matter signals. Some of the results are now understood to probably just be backgrounds, but not all of them have been understood yet. One of the most interesting parts is the discussion of the irreducible neutrino background. This will restrict the ability of future experiments to set limits, since once backgrounds appear the limits scale roughly with the square root of the exposure time rather than linearly. Fortunately, the time distributions are different, so the effect is not as bad as it could be.