Abstract
Title: "Holography, modified gravity and extra-dimensions"
Abstract:
Abstract: On this talk we will describe the brane-world scenario as a
mean to account for the late-time acceleration of the universe. We
will address two issues: on the one hand, we propose a generalised
induced gravity brane-world model where the brane action contains an
arbitrary f(R) term, R being the scalar curvature of the brane. We
show that the effect of the f(R) term on the dynamics of a homogeneous
and isotropic brane is twofold: (i) an evolving induced gravity
parameter and (ii) a shift on the energy density of the brane. This
new shift term, which is absent on the Dvali, Gabadadze and Porrati
(DGP) model, plays a crucial role to self-accelerate the generalised
normal DGP branch of our model. We analyse as well the stability of de
Sitter self-accelerating solutions under homogeneous perturbations and
compare our results with the standard 4-dimensional one. We will as
well apply a cosmographic approach to constrain the present model. On
the other hand, we present an holographic model of the DGP scenario
with a Gauss-Bonnet term in the bulk. We concentrate on the solution
that generalises the normal DGP branch. It is well known that this
branch cannot describe the late-time acceleration of the universe even
with the inclusion of a Gauss-Bonnet term. Here, we show that this
branch in the presence of a Gauss-Bonnet curvature effect and an
holographic dark energy with the Hubble scale as the infra-red cutoff
can describe the late-time acceleration of the universe. It is
worthwhile to stress that such an energy density component cannot do
the same job on the normal DGP branch (without Gauss-Bonnet
modifications) nor in a standard 4-dimensional relativistic model. The
acceleration on the brane is also presented as being induced through
an effective dark energy which corresponds to a balance between the
holographic one and geometrical effects encoded through the Hubble
parameter.