  Infrared regularized versions of 4-D N=1 superstring ground states are
constructed by curving the spacetime. A similar regularization can be performed
in field theory. For the IR regularized string ground states we derive the
exact one-loop effective action for non-zero U(1) or chromo-magnetic fields as
well as gravitational and axionic-dilatonic fields. This effective action is IR
and UV finite. Thus, the one-loop corrections to all couplings (gravitational,
gauge and Yukawas) are unabiguously computed. These corrections are necessary
for quantitative string superunification predictions at low energies. The
one-loop corrections to the couplings are also found to satisfy Infrared Flow
Equations.
