  The existence of an interpolating master action does not guarantee the same
spectrum for the interpolated dual theories. In the specific case of a
generalized self-dual (GSD) model defined as the addition of the Maxwell term
to the self-dual model in $D=2+1$, previous master actions have furnished a
dual gauge theory which is either nonlocal or contains a ghost mode. Here we
show that by reducing the Maxwell term to first order by means of an auxiliary
field we are able to define a master action which interpolates between the GSD
model and a couple of non-interacting Maxwell-Chern-Simons theories of opposite
helicities. The presence of an auxiliary field explains the doubling of fields
in the dual gauge theory. A generalized duality transformation is defined and
both models can be interpreted as self-dual models. Furthermore, it is shown
how to obtain the gauge invariant correlators of the non-interacting MCS
theories from the correlators of the self-dual field in the GSD model and
vice-versa. The derivation of the non-interacting MCS theories from the GSD
model, as presented here, works in the opposite direction of the soldering
approach.
