Dark matter in the Kim-Nilles mechanism
  The Kim-Nilles mechanism relates the $\mu$ term with the axion scale $f_a$,
leading to the axino-Higgsino-Higgs Yukawa coupling of order $\mu/f_a$. This
can bring a dangerous thermal production of axinos. If the axino is stable, its
mass has to be as small as ${\cal O}$(0.1keV), or the reheat temperature should
be lower than ${\cal O}$(10GeV) taking the lower axion scale $10^{10}$ GeV in
order not to overclose the Universe. If the axino decays to a neutralino, the
overproduced neutralinos can re-annihilate appropriately to saturate the
observed dark matter density if the annihilation rate is of order
$10^{-8}{GeV}^{-2}$ for the axion scale larger than about $10^{11}$ GeV. Thus,
a light Higgsino-like lightest supersymmetric particle with a sizable bino
mixture becomes a good dark matter candidate whose nucleonic cross-section is
of order $10^{-45}$cm$^2$.
