On the consistency of the expansion with the perturbations

Understand

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.