  The Green-Kubo relation for two models of granular gases is discussed. In the
Maxwell model in any dimension, the effective temperature obtained from the
Green-Kubo relation is shown to be frequency independent, and equal to the
average kinetic energy, known as the granular temperature. In the second model
analyzed, a mean-field granular gas, the collision rate of a particle is taken
to be proportional to its velocity. The Green-Kubo relation in the high
frequency limit is calculated for this model, and the effective temperature in
this limit is shown to be equal to the granular temperature. This result, taken
together with previous results, showing a difference between the effective
temperature at zero frequency (the Einstein relation) and the granular
temperature, shows that the Green-Kubo relation for granular gases is violated.
