  The axino is a promising candidate for dark matter in the Universe. It is
electrically and color neutral, very weakly interacting, and could be - as
assumed in this study - the lightest supersymmetric particle, which is stable
for unbroken R-parity. In supersymmetric extensions of the standard model, in
which the strong CP problem is solved via the Peccei-Quinn mechanism, the axino
arises naturally as the fermionic superpartner of the axion. We compute the
thermal production rate of axinos in supersymmetric QCD. Using hard thermal
loop resummation, we obtain a finite result in a gauge-invariant way, which
takes into account Debye screening in the hot quark-gluon-squark-gluino plasma.
The relic axino abundance from thermal scatterings after inflation is
evaluated. We find that thermally produced axinos could provide the dominant
part of cold dark matter, for example, for an axino mass of 100 keV and a
reheating temperature of 10^6 GeV.
