On the Heterotic Effective Action at One Loop Gauge Couplings and the Gravitational Sector

We present in detail the procedure for calculating the heterotic one-loop effective action. We focus on gravitational and gauge couplings. We show that the two-derivative couplings of the gravitational sector are not renormalized at one loop when the ground state is supersymmetric. Arguments are presented that this non-renormalization theorem persists to all orders in perturbation theory. Arguments are presented that this non-renormalization theorem persists to all orders in perturbation theory. We also derive the full one-loop correction to the gauge coupling. For a class of N = 2 ground states, namely those that are obtained by toroidal compactification to four dimensions of generic six-dimensional N = 1 models, we give an explicit formula for the gauge-group independent thresholds, and show that these are equal within the whole family. To appear in the proceedings of the 5th Hellenic School and Workshops on Elementary Particle Physics, Corfu, Greece, 3–24 September 1995. CERN-TH/96-91 SISSA/60/96/EP April 1996 ∗ On leave from Centre National de la Recherche Scientifique, France. ⋄ On leave from Division of Theoretical Physics, Physics Department, University of Ioannina, Greece.