Searching for Scalar Dark Matter in Atoms and Astrophysical Phenomena:
  Variation of Fundamental Constants
  We propose to search for scalar dark matter via its effects on the
electromagnetic fine-structure constant and particle masses. Scalar dark matter
that forms an oscillating classical field produces `slow' linear-in-time drifts
and oscillating variations of the fundamental constants, while scalar dark
matter that forms topological defects produces transient-in-time variations of
the constants of Nature. These variations can be sought for with atomic clock,
laser interferometer and pulsar timing measurements. Atomic spectroscopy and
Big Bang nucleosynthesis measurements already give improved bounds on the
quadratic interaction parameters of scalar dark matter with the photon,
electron, and light quarks by up to 15 orders of magnitude, while Big Bang
nucleosynthesis measurements provide the first such constraints on the
interaction parameters of scalar dark matter with the massive vector bosons.
