  It is conjectured that the world-volume action of a probe D3-brane in an
$AdS_5 \times S^5$ background of type IIB superstring theory, with one unit of
flux, can be reinterpreted as the exact effective action (or highly effective
action) for U(2), ${\cal N} = 4$ super Yang-Mills theory on the Coulomb branch.
An analogous conjecture for $U(2)_k \times U(2)_{-k} $ ABJM theory is also
presented. The main evidence supporting these conjectures is that the brane
actions have all of the expected symmetries and dualities. Highly effective
actions have general coordinate invariance, even though they describe
nongravitational theories.
