488 research outputs found
Evolution of linear cosmological perturbations and its observational implications in Galileon-type modified gravity
A scalar-tensor theory of gravity can be made not only to account for the
current cosmic acceleration, but also to satisfy solar-system and laboratory
constraints, by introducing a non-linear derivative interaction for the scalar
field. Such an additional scalar degree of freedom is called "Galileon". The
basic idea is inspired by the DGP braneworld, but one can construct a
ghost-free model that admits a self-accelerating solution. We perform a fully
relativistic analysis of linear perturbations in Galileon cosmology. Although
the Galileon model can mimic the background evolution of standard CDM
cosmology, the behavior of perturbation is quite different. It is shown that
there exists a super-horizon growing mode in the metric and Galileon
perturbations at early times, suggesting that the background is unstable. A
fine-tuning of the initial condition for the Galileon fluctuation is thus
required in order to promote a desirable evolution of perturbations at early
times. Assuming the safe initial condition, we then compute the late-time
evolution of perturbations and discuss observational implications in Galileon
cosmology. In particular, we find anticorrelations in the cross-correlation of
the integrated Sachs-Wolfe effect and large scale structure, similar to the
normal branch of the DGP model.Comment: 15 pages, 11 figures; v2: References added, typos correcte
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