Review of axino dark matter

Understand

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.