One loop calculation of coupling constants in IR-regulated string theory

Exact Superstring solutions are constructed moving in 4-D space-time with positive curvature and non-trivial dilaton and antisymmetric tensor fields. The full spectrum of string excitations is derived as a function of moduli fields T^{i} and the scale \mu^2=1/(k+2) which induced by the non-zero background fields. The spectrum of string excitations has a non-zero mass gap \mu^2 and in the weak curvature limit (\mu small) \mu^2 plays the role of a well defined infrared regulator, consistent with modular invariance, gauge invariance, supersymmetry and chirality. 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 (gravitational, gauge and Yukawas) are unambiguously computed and are finite both in the Ultra-Violet and the Infra-Red regime. These corrections are necessary for quantitative string superunification predictions at low energies. Similar calculations are done in the effective field theory. The one-loop corrections to the couplings are also found to satisfy Infrared Flow Equations.