Non-parametric Reconstruction of Growth Index via Gaussian Processes

Abstract

The accelerated cosmic expansion could be due to dark energy within general relativity (GR), or modified gravity. It is of interest to differentiate between them, by using both the expansion history and the growth history. In the literature, it was proposed that the growth index $\gamma$ is useful to distinguish these two scenarios. In this work, we consider the non-parametric reconstruction of the growth index $\gamma$ as a function of redshift $z$ from the latest observational data as of July 2018 via Gaussian Processes. We find that $f(R)$ theories and dark energy models within GR (especially $\Lambda$CDM) are inconsistent with the results in the moderate redshift range far beyond $3\sigma$ confidence level. A modified gravity scenario different from $f(R)$ theories is favored. However, these results can also be due to other non-trivial possibilities, in which dark energy models within GR (especially $\Lambda$CDM) and $f(R)$ theories might still survive. In all cases, our results suggest that new physics is required.

arXiv comment12 pages, 9 figures, revtex4; v2: discussions added, SCPMA in press; v3: final version

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• Multiple measurements of quasars acting as standard probes: model independent calibration and exploring the Dark Energy Equation of States
• Gaussian Process Approach for Model-Independent Reconstruction of $f(Q)$ Gravity with Direct Hubble Measurements
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• Observational Constraints on Growth Index with Cosmography
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