#### March 21, 14:15 in A315

#### Ippocratis Saltas (Sussex U., Brighton, UK)

#### f(R) gravity from the renormalisation group

I will discuss the cosmology resulting from a Renormalisation Group
(RG) improvement of the Einstein--Hilbert action, in the context of
the Asymptotic Safety scenario, where both Newton's and cosmological
constant run with the energy scale. In particular, I will focus on
viewing the RG improved action as an effective f(R) model and then
discuss its corresponding cosmological UV and IR dynamics.
As I will show, the effective f(R) model has some remarkable
properties: It naturally describes a non-singular Universe, giving
rise to a primordial and late time acceleration period, with
exponentially separated scales, on the same time exhibiting a
radiation and matter domination era. I will also explain how the model
behaves as R^2 gravity at very high energies, while it correctly
recovers General Relativity at solar system scales. Finally, I will
discuss about the primordial fluctuations, which in this simplified
model turn out to be too large to be the observed ones, and more
ingredients in the action are needed.