  For the Randall-Sundrum brane world where a positive tension Minkowski brane
is embedded in AdS5, two candidate propagators have been suggested in the
literature, one being based on the normalized mode solutions to the source-free
volcano potential fluctuation equation, and the other being the Giddings, Katz
and Randall outgoing Hankel function based one. We show that while both of
these two propagators have the same pole plus cut singularity structure in the
complex energy plane, they behave differently on their respective circles at
infinity, as a consequence of which only the Hankel function based propagator
proves to be causal, with the normalized mode based one being found to take
support outside the AdS5 lightcone. In addition we show that unlike the Hankel
function based propagator, the normalized mode based propagator does not
correctly implement the junction conditions which hold in the presence of a
perturbative source on the brane.
