Search for transient variations of the fine structure constant and dark
  matter using fiber-linked optical atomic clocks
  We search for transient variations of the fine structure constant using data
from a European network of fiber-linked optical atomic clocks. By searching for
coherent variations in the recorded clock frequency comparisons across the
network, we significantly improve the constraints on transient variations of
the fine structure constant. For example, we constrain the variation in alpha
to <5*10^-17 for transients of duration 10^3 s. This analysis also presents a
possibility to search for dark matter, the mysterious substance hypothesised to
explain galaxy dynamics and other astrophysical phenomena that is thought to
dominate the matter density of the universe. At the current sensitivity level,
we find no evidence for dark matter in the form of topological defects (or,
more generally, any macroscopic objects), and we thus place constraints on
certain potential couplings between the dark matter and standard model
particles, substantially improving upon the existing constraints, particularly
for large (>~10^4 km) objects.
