We find that tachyonic orbifold examples of AdS/CFT have corresponding
instabilities at small radius, and can decay to more generic gauge theories. We
do this by computing a destabilizing Coleman-Weinberg effective potential for
twisted operators of the corresponding quiver gauge theories, generalizing
calculations of Tseytlin and Zarembo and interpreting them in terms of the
large-N behavior of twisted-sector modes. The dynamically generated potential
involves double-trace operators, which affect large-N correlators involving
twisted fields but not those involving only untwisted fields, in line with
large-N inheritance arguments. We point out a simple reason that no such small
radius instability exists in gauge theories arising from freely acting
orbifolds, which are tachyon-free at large radius. When an instability is
present, twisted gauge theory operators with the quantum numbers of the
large-radius tachyons aquire VEVs, leaving a gauge theory with fewer degrees of
freedom in the infrared, analogous to but less extreme than ``decays to
nothing'' studied in other systems with broken supersymmetry. In some cases one
is left with pure glue QCD plus decoupled matter and U(1) factors in the IR,
which we thus conjecture is described by the corresponding (possibly strongly
coupled) endpoint of tachyon condensation in the M/String-theory dual.Comment: 28 pages, harvmac big. v2: references added; improved discussion of
RG improvemen
