Observational constraints on growth index with cosmography

• Published in: The European physical journal. C, Particles and fields Vol. 79; no. 8; pp. 1 - 12
• Main Authors: Yin, Zhao-Yu, Wei, Hao
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.08.2019; Springer; Springer Nature B.V; SpringerOpen
• Subjects: Analysis; Astronomy; Astrophysics and Cosmology; Confidence intervals; Dark energy; Elementary Particles; Hadrons; Heavy Ions; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Red shift; Regular Article - Theoretical Physics; String Theory; Taylor series
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-019-7191-8

In the literature, it was proposed that the growth index 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 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 γ ( z ) as a Taylor series with respect to redshift z or y -shift, y = z / ( 1 + z ) . We find that the present value γ 0 = 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, γ 0 ≃ 0.55 (for dark energy models in GR) can be consistent with the latest observational data at 1 σ C.L. in five of the nine cases under consideration, but is inconsistent beyond 2 σ C.L. in the other four cases (while it is still consistent within the 3 σ region). Thus, we can say nothing firmly about γ 0 ≃ 0.55 . We also find that a varying γ ( z ) is favored.