  We revisit the cosmology of the supersymmetric QCD axion, highlighting the
existence of a serious cosmological axino problem that is fully analogous to
the gravitino problem of overclosure via thermal production. A general analysis
implies that the QCD axino has a mass greater than or equal to that of the
gravitino in the absence of unnatural fine-tuning or sequestering. As a
consequence, bounds from thermal gravitino and QCD axino production are
complementary in parameter space, and together provide a quite stringent limit
on the reheating temperature after inflation given by T_R < 10^3 - 10^6 GeV for
an axion decay constant of f_a = 10^9 - 10^12 GeV. Motivated by this result, we
explore the cosmology of gravitino LSP and axino NLSP at low T_R and present
three realistic scenarios for dark matter.

High Energy Physics - Phenomenology