Abstract
We present an analytical fit to the growth function of the dark matter perturbations when dark energy perturbations are present. The growth index γ depends upon the dark energy equation of state w, the speed of sound of the dark energy fluctuations, the dark matter abundance and the observed comoving scale. The growth index changes by O(5%) for small speed of sound and large deviations of w from −1 with respect to its value in the limit of no dark energy perturbations.
Highlights
Current observations of Type Ia supernovae luminosity distances indicate that our Universe is in a phase of accelerated expansion [1]
In this Letter we study the effect of dark energy perturbations on the growth index γ
See for instance [39], and to simplify the analysis, we will assume that the speed of sound associated with the dark energy perturbations and the equation of state do not change appreciably in the proper time range and that the dark energy perturbations have no shear
Summary
Current observations of Type Ia supernovae luminosity distances indicate that our Universe is in a phase of accelerated expansion [1]. See for instance [39], and to simplify the analysis, we will assume that the speed of sound associated with the dark energy perturbations and the equation of state do not change appreciably in the proper time range and that the dark energy perturbations have no shear This is a good approximation in linear perturbation theory for dark energy models with a scalar field. Under these assumptions, we provide an analytical formula for the growth index γ as a function of the speed of sound, the equation of state w, the dark matter abundance and the comoving scale.
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