A Separate Universe Approach to Quintessence Perturbations

Nuclear Physics B - Proceedings Supplements (Impact Factor: 0.88). 03/2005; DOI: 10.1016/j.nuclphysbps.2005.04.050
Source: arXiv

ABSTRACT There is some observational evidence that the dark energy may not be smooth on large scales. This makes it worth while to try and get as simple and as intuitive a picture of how dark energy perturbations behave so as to be able to better constrain possible models of dark energy and the generation of large scale perturbations. The separate Universe method provides an easy way to evaluate cosmological perturbations, as all that is required is an understanding of the background behavior. Here, this method is used to show how the size of the dark energy perturbations, preferred by observations, is larger than would be expected, and so some mechanism may be required to amplify them. Comment: 11 pages. v2: References added

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have studied constraints on the equation of state, $w$, and speed of sound, c_s, of the dark energy from a joint analysis of data from the cosmic microwave background, large scale structure and type-Ia supernovae. We find that current observations have no significant sensitivity to c_s. However, there is a slight difference between models in which there are no dark energy perturbations and models in which dark energy behaves as a fluid. Assuming that there are no dark energy perturbations shifts the allowed region for $w$ to slightly higher values. At present models with and without dark energy perturbations provide roughly equally good fits to observations, but the difference is potentially important for future parameter estimations. Finally, we have also performed error forecasts for future measurements of c_s. Comment: 9 pages, 6 figures, Revtex
    Physical review D: Particles and fields 04/2005;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose a model which produces dark energy perturbations large enough to explain the lack of power seen at the quadrupole scale in the cosmic microwave background. If the dark energy is frozen from horizon exit during inflation until dark energy domination, then it is not possible to have perturbations in the dark energy which are large enough. We propose using a tachyonic amplification mechanism to overcome this. The dark energy is taken to be a complex scalar field, where the radial field has a Mexican hat potential. During inflation, the radial component is trapped near the maximum of its potential. At the end of inflation, it rolls down to the minimum. The dark energy today is taken to be a pseudo-Nambu-Goldstone boson. The perturbations generated during inflation are amplified by the rolling of the radial field. We also examine the use of the variable decay mechanism in order to generate an anti-correlation between the dark energy perturbations and the curvature perturbation. We show that using this mechanism then constrains the properties of the dark energy and its evolution from redshift one until today.
    Physical review D: Particles and fields 04/2005; 71(12).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Intuitively we might expect dark energy, which gravitationally behaves as repulsive form of matter, will not cluster on large scales. In this paper, we present a simple set of argument which leads to the conclusion that perturbations in dark matter imply perturbations in dark energy if $p \neq -\rho$. We estimate the amplitude of the perturbation in dark energy at different length scales for a quintessence model with an exponential potential. We show that on length scales much smaller than hubble radius, perturbations in dark energy is negligible in comparison to the perturbations in dark matter. However, on scales comparable to the hubble radius ($\lambda_{p}>1000\mathrm{Mpc}$) the perturbation in dark energy in general cannot be neglected. As compared to the $\Lambda$CDM model, large scale matter perturbation is suppressed in generic dark energy models.
    Physical review D: Particles and fields 02/2008;


Available from