  Stability of AdS space allows scalar fields to have negative mass squared as
long as the Breitenlohner-Freedman bound is satisfied. In a compactification of
AdS instead, to avoid instabilities, a tachyonic bulk mass must be supplemented
by appropriate brane actions. In this paper we clarify the meaning of the lower
bound in the Randall-Sundrum scenario with two branes and explain how the
instability disappears in the infinite space limit. A CFT interpretation is
also given as radiative symmetry breaking.
