The axino with mass in the GeV region can be cold dark matter ( CDM ) in the galactic halo .
However , if R-parity is broken , for example by the bilinear terms \mu _ { \alpha } , then axino ( \tilde { a } ) can decay to \nu + \gamma .
In this case , the most stringent bound on the axino lifetime comes from the diffuse photon background and we obtain that the axino lifetime should be greater than 3.9 \times 10 ^ { 24 } \Omega _ { \tilde { a } } h s which amounts to a very small bilinear R-parity violation , i.e . \mu _ { \alpha } < 1 keV .
This invalidates the atmospheric neutrino mass generation through bilinear R-violating terms within the context of axino CDM .

[ Key words : dark matter , axino , R-parity violation , detection of CDM ]