Alternative dark matter candidates: Axions
  The axion is arguably one of the best motivated candidates for dark matter.
For a decay constant greater than about 10^9 GeV, axions are dominantly
produced non-thermally in the early universe and hence are "cold", their
velocity dispersion being small enough to fit to large scale structure.
Moreover, such a large decay constant ensures the stability at cosmological
time scales and its behaviour as a collisionless fluid at cosmological length
scales. Here, we review the state of the art of axion dark matter predictions
and of experimental efforts to search for axion dark matter in laboratory
experiments.
