A note on the RG flow in (N=1, D=4) supergravity and applications to Z3 orbifold/orientifold compactification Original Research Article

We apply the standard approach of RG flow for the gauge couplings in N=1, D=4 supergravity to show how to match its results with the heterotic Z3 orbifold and type IIB Z3 orientifold-based models. Using only supergravity, anomaly cancellation and the requirement of unification we determine the part of the Kähler potential of the model invariant under the symmetries of the model. For heterotic orbifolds/type IIB orientifolds, this shows that the lowest order Kähler term of the dilaton has the structure −ln(S+S) in agreement with string calculations. The structure of the holomorphic coupling is also found from arguments of unification and anomaly cancellation under the conjectured SL(2,Z)Ti symmetries of the models. A consequence of the latter is that in the case of the Z3 orientifold the holomorphic coupling necessarily contains a part with coefficient proportional to the one loop beta function, in agreement with string calculations which do not however assume this symmetry. This gives circumstantial evidence for the existence of this symmetry at string level in Z3 orientifold. Finally, we comment on the values of the unification scale and examine the possibility of mirage unification in which the effective unification scale may be situated far above the string scale.