Light mediators in dark matter direct detections
  In an extended effective operator framework, we investigate in detail the
effects of light mediators on the event spectra of dark matter (DM)-nucleus
scatterings. The presence of light mediators changes the interpretation of the
current experimental data, especially the determination of DM particle mass. We
show by analytic and numerical illustrations that for all the operators
relevant to spin-independent scatterings, the DM particle mass allowed by the
data increases significantly when the mediator particle becomes lighter. For
the data of CDMS-II-Si, the allowed DM particle mass can reach $\sim 50$ GeV,
depending on the type of operators, and the increase of DM particle mass
saturates when the mediator mass is below $\mathcal{O}(10)$ MeV. The upper
limits from other experiments such as SuperCDMS, CDMSlite, CDEX, XENON10/100,
LUX, PandaX etc. all tend to be weaker toward high DM mass regions. In a
combined analysis, we show that the presence of light mediators can partially
relax the tension in the current results of CDMS-II-Si, SuperCDMS and LUX.
