Direct dark matter detection: The diurnal variation in directional
  experiments
  We present some theoretical results relevant to the direct dark matter
detection experiments, paying particular attention to directional experiments,
i.e. experiments in which, not only the energy but the direction of the
recoiling nucleus is observed. In directional experiments the detection rate
depends on the angle between the line observation and the sun's direction of
motion. Since, however, the direction of observation is fixed with respect the
earth, while the Earth is rotating around its axis, in a directional experiment
the angle between the direction of observation and the Sun's direction of
motion will change during the day. So the observed signal in such experiments
will exhibit a very interesting and characteristic periodic diurnal variation.
