{
  "id": "1805.08230",
  "version": "v1",
  "published": "2018-05-21T18:02:52.000Z",
  "updated": "2018-05-21T18:02:52.000Z",
  "title": "On the consistency of the expansion with the perturbations",
  "authors": [
    "Radouane Gannouji",
    "David Polarski"
  ],
  "comment": "8 pages, 10 figures",
  "categories": [
    "astro-ph.CO",
    "gr-qc"
  ],
  "abstract": "Assuming a simple form for the growth index gamma(z) depending on two parameters gamma_0 = gamma(z=0) and gamma_1 = gamma'(z=0), we show that these parameters can be constrained using background expansion data. We explore systematically the preferred region in this parameter space. Inside General Relativity we obtain that models with a quasi-static growth index and gamma_1 = -0.02 are favoured. We find further the lower bounds gamma_0 > 0.53 and gamma_1 > -0.15 for models inside GR. Models outside GR having the same background expansion as LCDM and arbitrary gamma(z) with gamma_0 = gamma_0^{LCDM}, satisfy G_{eff,0}>G for gamma_1 > gamma_1^{LCDM}, and G_{eff,0}<G for gamma_1 < gamma_1^{LCDM}. The first models will cross downwards the value G_{eff}=G on very low redshifts z<0.3, while the second models will cross upwards G_{eff}=G in the same redshift range. This makes the realization of such modified gravity models even more problematic.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-05-21T18:02:52.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "consistency",
      "perturbations",
      "growth index gamma",
      "models outside gr",
      "background expansion data"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}