Scalaron dynamics from UV to IR

Understand

We consider a scenario where the scalaron of $f({\cal R})$ models is related to the volume modulus of string compactifications leaving only one scalar degree of freedom at low energy.

• The coefficient of the leading curvature squared contribution to the low energy effective action of gravity determines the mass of the scalaron.
• We impose that this mass is small enough to allow for the scalaron to drive Starobinski's inflation.
• After inflation, the renormalisation group evolution of the couplings of the $f({\cal R})$ theory, viewed as a scalar-tensor theory, provides the link with the Infra-Red regime.