Composite dark matter and direct-search experiments

The results of the direct searches for dark matter are reinterpreted in the
framework of composite dark matter, i.e. dark matter particles that form
neutral bound states, generically called “dark atoms”.
Two different scenarios are presented: milli-interacting dark matter and
dark anti-atoms. In both of them, dark matter interacts sufficiently strongly
with terrestrial matter to be stopped in it before reaching underground detec-
tors, which are typically located at a depth of 1 km. As they drift towards the
center of the earth because of gravity, these thermal dark atoms are radiatively
captured by the atoms of the active medium of underground detectors, which
causes the emission of photons that produce the signals through their interac-
tions with the electrons of the medium. This provides a way of reinterpreting
the results in terms of electron recoils instead of nuclear recoils.
The two models involve milli-charges and are able to reconcile the most
contradictory experiments. We determine, for each model, the regions in the
parameter space that reproduce the experiments with positive results in con-
sistency with the constraints of the experiments with negative results.