Observational constraints on growth index with cosmography

• Main Authors: Zhao-Yu Yin, Hao Wei
• Format: Article
• Language: English
• Published: SpringerOpen 2019-08-01
• Series: European Physical Journal C: Particles and Fields
• Online Access: http://link.springer.com/article/10.1140/epjc/s10052-019-7191-8

Abstract In the literature, it was proposed that the growth index $$\gamma $$ γ is useful to distinguish the scenarios of dark energy and modified gravity. In the present work, we consider the constraints on the growth index $$\gamma $$ γ by using the latest observational data. To be model-independent, we use cosmography to describe the cosmic expansion history, and also expand the general $$\gamma (z)$$ γ(z) as a Taylor series with respect to redshift z or y-shift, $$y=z/(1+z)$$ y=z/(1+z) . We find that the present value $$\gamma _0=\gamma (z=0)\simeq 0.42$$ γ0=γ(z=0)≃0.42 (for most of viable f(R) theories) is inconsistent with the latest observational data at high confidence level (C.L.). On the other hand, $$\gamma _0\simeq 0.55$$ γ0≃0.55 (for dark energy models in GR) can be consistent with the latest observational data at $$1\sigma $$ 1σ C.L. in five of the nine cases under consideration, but is inconsistent beyond $$2\sigma $$ 2σ C.L. in the other four cases (while it is still consistent within the $$3\sigma $$ 3σ region). Thus, we can say nothing firmly about $$\gamma _0\simeq 0.55$$ γ0≃0.55 . We also find that a varying $$\gamma (z)$$ γ(z) is favored.