ONE-LOOP CALCULATION OF COUPLING-CONSTANTS IN IR REGULATED STRING THEORY

Exact Superstring solutions are constructed moving in 4-D space-time w ith positive curvature and non-trivial dilaton and antisymmetric tenso r fields. The full spectrum of string excitations is derived as a func tion of moduli fields T-i and the scale mu(2) = 1/(k + 2) which induce d by the non-zero background fields. The spectrum of string excitation s has a non-zero mass gap mu(2) and in the weak curvature limit (mu sm all) mu(2) plays the role of a well defined infrared regulator, consis tent with modular invariance, gauge invariance, supersymmetry and chir ality. The effects of a covariantly constant chomo-magnetic field B as well as additional curvature can be derived exactly up to one string- loop level. Thus, the one-loop corrections to all couplings (gravitati onal, gauge and Yukawas) are unambiguously computed and are finite bot h in the Ultra-Violet and the Infra-Red regime. 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.