Review of axino dark matter
  We review the status of axino dark matter. Two hierarchy problems, the strong
CP problem and the gauge hierarchy problem, have led to introducing into
particle physics a spontaneously broken global Peccei-Quinn symmetry and a
softly broken supersymmetry, respectively. Combining them implies the presence
of not only an axion, but also of its scalar component, saxion, and their
fermionic partner, axino. Among these, the axion and the axino are attractive
dark matter candidates. Various possibilities for the axino as dark matter are
discussed.
