  Light scalars appear in many well-motivated extensions of the Standard Model
including supersymmetric models with additional gauge singlets. Such scalars
could mediate the interactions between dark matter and nuclei, giving rise to
the tentative signals observed by several dark matter direct detection
experiments including CDMS-Si. In this letter, we derive strong new limits on
light scalar mediators by using the LHCb, Belle and BaBar searches for rare
$\Upsilon$ and B decays. These limits rule out significant parts of the
parameter space favored by CDMS-Si. Nevertheless, as current searches are not
optimized for investigating weakly coupled light scalars, a further increase in
experimental sensitivity could be achieved by relaxing requirements in the
event selection.
