Tachyons in a slice of AdS

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 Letter 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.