Breaking degeneracies in modified gravity with higher (than 2nd) order weak-lensing statistics

Austin Peel,Marco Baldi,Carlo Giocoli,Valeria Pettorino,Jean-Luc Starck

doi:10.1051/0004-6361/201833481

Abstract

General relativity (GR) has been well tested up to solar system scales, but it is much less certain that standard gravity remains an accurate description on the largest, that is cosmological, scales. Many extensions to GR have been studied that are not yet ruled out by the data, including by that of the recent direct gravitational wave detections. Degeneracies among the standard model (ΛCDM) and modified gravity (MG) models, as well as among different MG parameters, must be addressed in order to best exploit information from current and future surveys and to unveil the nature of dark energy. We propose various higher-order statistics in the weak-lensing signal as a new set of observables able to break degeneracies between massive neutrinos and MG parameters. We have tested our methodology on so-called f(R) models, which constitute a class of viable models that can explain the accelerated universal expansion by a modification of the fundamental gravitational interaction. We have explored a range of these models that still fit current observations at the background and linear level, and we show using numerical simulations that certain models which include massive neutrinos are able to mimic ΛCDM in terms of the 3D power spectrum of matter density fluctuations. We find that depending on the redshift and angular scale of observation, non-Gaussian information accessed by higher-order weak-lensing statistics can be used to break the degeneracy between f(R) models and ΛCDM. In particular, peak counts computed in aperture mass maps outperform third- and fourth-order moments.

Highlights

Current observations from the cosmic microwave background (CMB) anisotropies, baryon acoustic oscillations, and supernova luminosity distances all support a phase of accelerated cosmic expansion during the present epoch (e.g. Planck Collaboration XIII 2016; Planck Collaboration XIV 2016; Anderson et al 2014; Betoule et al 2014)
We have tested our methodology on so-called f (R) models, which constitute a class of viable models that can explain the accelerated universal expansion by a modification of the fundamental gravitational interaction
Our goal is to look beyond second-order statistics to see if it is possible to distinguish the modified gravity (MG) models from ΛCDM

Summary

Introduction

Current observations from the cosmic microwave background (CMB) anisotropies, baryon acoustic oscillations, and supernova luminosity distances all support a phase of accelerated cosmic expansion during the present epoch (e.g. Planck Collaboration XIII 2016; Planck Collaboration XIV 2016; Anderson et al 2014; Betoule et al 2014) The cause of such evolution is still unknown and should amount to approximately 70% of the total energy density of the Universe. The cosmic expansion of a ΛCDM model, can be mimicked by vast range of models, which are in agreement with current observations These scenarios typically assume either a fluid component, in other words, dark energy (DE), or a modification of general relativity at large scales. Even when considering linear perturbations and the impact on CMB, dark energy and modified gravity (MG) models are still viable (Planck Collaboration XIV 2016) and may be advocated to solve tensions currently present between Planck data and late time probes, such as weak lensing (Hildebrandt et al 2017; DES Collaboration 2018) and, in smaller measure, redshift space distortions (Planck Collaboration XIV 2016)

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Conclusion