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arXiv · 0912.4641

Evolution of linear cosmological perturbations and its observational implications in Galileon-type modified gravity

Tsutomu Kobayashi·Hiroyuki Tashiro·Daichi Suzuki
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Abstract

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 $Λ$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.

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Tsutomu Kobayashi, Hiroyuki Tashiro, Daichi Suzuki. 2010-03-18. Evolution of linear cosmological perturbations and its observational implications in Galileon-type modified gravity. https://doi.org/10.1103/physrevd.81.063513

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