  We study the decoupling effects in N=1 (global) supersymmetric theories with
chiral superfields at the one-loop level. The examples of gauge neutral chiral
superfields with the minimal (renormalizable) as well as non-minimal (non-
renormalizable) couplings are considered, and decoupling in gauge theories with
U(1) gauge superfields that couple to heavy chiral matter is studied. We
calculate the one-loop corrected effective Lagrangians that involve light
fields and heavy fields with mass of order M. The elimination of heavy fields
by equations of motion leads to decoupling effects with terms that grow
logarithmically with M. These corrections renormalize light fields and
couplings in the theory (in accordance with the "decoupling theorem"). When the
field theory is an effective theory of the underlying fundamental theory, like
superstring theory, where the couplings are calculable, such decoupling effects
modify the low-energy predictions for the effective couplings of light fields.
In particular, for the class of string vacua with an "anomalous" U(1) the
vacuum restabilization triggers the decoupling effects, which can significantly
modify the low energy predictions for the couplings of the surviving light
fields. We also demonstrate that quantum corrections to the chiral potential
depending on massive background superfields and corresponding to supergraphs
with internal massless lines and external massive lines can also arise at the
two-loop level.
