  The equations for the evolution of a homogeneous brane world that emits
gravitons at early times, and into a non-Z_2 symmetric bulk, are derived using
an AdS-Vaidya spacetime approximation. The behaviour of the black hole mass
parameters either side of the brane is analysed, and it is found that in
general graviton emission leads to a decrease in the non-Z_2 symmetry. However,
the behaviour of the dark radiation term in the Friedmann equation is more
complex: it is shown that this term can increase or decrease due to the non-Z_2
symmetry, and can become negative in some cases, leading to H=0 and the brane
universe collapsing. Constraints on the initial (nonzero) sizes of the mass
parameters are therefore derived.
