  The cosmological (upper) limit on the Peccei-Quinn constant, related to the
primordial oscillations of the axion field, can be relaxed for a mirror axion
model. The simple reason is that the mirror world is colder and so the behavior
of the axion temperature-dependent mass is dominated by the contribution from
the mirror sector. So the coherent oscillations start earlier and
correspondingly the axion mass density \Omega_a h^2 is reduced.
