Long-range forces in direct dark matter searches

We discuss the positive indications of a possible dark matter signal in direct detection experiments in terms of a mechanism of interaction between the dark matter particle and the nuclei occurring via the exchange of a light mediator, resulting in a long-range interaction. We analyze the annual modulation results observed by the DAMA and CoGeNT experiments and the observed excess of events of CRESST. In our analysis, we discuss the relevance of uncertainties related to the velocity distribution of galactic dark matter and to the channeling effect in NaI. We find that a long-range force is a viable mechanism, which can provide full agreement between the reconstructed dark matter properties from the various experimental data sets, especially for masses of the light mediator in the 10-30 MeV range and a light dark matter with a mass around 10 GeV. The relevant bounds on the light mediator mass and scattering cross section are then derived, should the annual modulation effects be due to this class of long-range forces.