  In non-supersymmetric orbifolds of N =4 super Yang-Mills, conformal
invariance is broken by the logarithmic running of double-trace operators -- a
leading effect at large N. A tachyonic instability in AdS_5 has been proposed
as the bulk dual of double-trace running. In this paper we make this
correspondence more precise. By standard field theory methods, we show that the
double-trace beta function is quadratic in the coupling, to all orders in
planar perturbation theory. Tuning the double-trace coupling to its (complex)
fixed point, we find conformal dimensions of the form 2 + i b, as formally
expected for operators dual to bulk scalars that violate the stability bound.
We also show that conformal invariance is broken in perturbation theory if and
only if dynamical symmetry breaking occurs. Our analysis is applicable to a
general large N field theory with vanishing single-trace beta functions.
