Cosmologically stabilizing radion along with the dilaton is one of the major
concerns of low energy string theory. One can hope that T and S dualities can
provide a plausible answer. In this work we study the impact of S and T duality
invariances on dilaton gravity. We have shown various instances where
physically interesting models arise as a result of imposing the mentioned
invariances. In particular S duality has a very privileged effect in that the
dilaton equations partially decouple from the evolution of the scale factors.
This makes it easy to understand the general rules for the stabilization of the
dilaton. We also show that certain T duality invariant actions become S duality
invariance compatible. That is they mimic S duality when extra dimensions
stabilize.Comment: Corrected a misleading interpretation of the S duality transformation
and a wrong comment on d=10. I thank A.Kaya for pointing this out to me in
time. So the new version is dealing with d=10 only. Added references and
corrected some typos. Minor re-editing. Omitted a section for elaboration in
a further study. Corrected further typo
