On gauge couplings in string theory Original Research Article

We investigate the field dependence of the gauge couplings of N = 1 string vacua from the point of view of the low energy effective quantum field theory. We find that field-theoretical considerations severely constrain the form of the string loop corrections; in particular, the dilaton dependence of the gauge couplings is completely universal at the one-loop level. The moduli dependence of the string threshold corrections is also constrained, and we illustrate the power of such constraints with a detailed discussion of the orbifold vacua and the (2,2) (Calabi-Yau) vacua of the heterotic string.