Chameleon screening in cosmic voids

Abstract

A key goal in cosmology in the upcoming decade will be to form a better understanding of the accelerated expansion of the Universe. Upcoming surveys, such as the Vera C. Rubin Observatory's 10-year Legacy Survey of Space and Time (LSST), Euclid and the Square Killometer Array (SKA) will deliver key datasets required to tackle this and other puzzles in contemporary cosmology. With this data, constraints of unprecedented power will be put on different models of dark energy and modified gravity. In this context it is crucial to understand how screening mechanisms, which hide the deviations of these theories from the predictions of general relativity in local experiments, affect structure formation. In this work we approach this problem by using a combination of analytic and numerical methods to describe chameleon screening in the context of cosmic voids. We apply a finite element method (FEM) code, SELCIE, to solve the chameleon equation of motion for a number of void profiles derived from observational data and simulations. The obtained results indicate a complex relationship between the properties of cosmic voids and the size of the chameleon acceleration of a test particle. We find that the fifth force on a test particle in a void is primarily related to the depth and the inner density gradient of the void. For realistic void profiles, the obtained chameleon-to-Newtonian acceleration ratios range between aϕ /aNewt ≈ 10-6– 10-5. However, it should be noted that in unusually deep voids with large inner density gradients, the acceleration ratios can be significantly higher. Similarly, other chameleon models, such as f(R) Hu-Sawicki theory allow for significantly higher acceleration ratios. Given these results, we also discuss the optimal density profiles for detecting the fifth force in the upcoming observational surveys.

Why cosmic voids matter: nonlinear structure & linear dynamics

“…Nevertheless, in analogy to halos, cosmic voids exhibit universal characteristics, such as the shape of their radial density profile [22,23]. The latter has become a focus of interest in itself with numerous recent follow-up studies, both in the context of ΛCDM [e.g., [24][25][26][27][28][29][30][31][32][33], as well as with the aim of exploring modifications to general relativity (GR) [e.g., [34][35][36][37][38][39][40][41][42][43][44], the impact of massive neutrinos [e.g., [45][46][47][48][49][50][51][52] and models of particle dark matter [e.g., [53][54][55][56][57].…”

Modeling and Testing Screening Mechanisms in the Laboratory and in Space

“…[56] and offers an implementation of chameleon theories in 2 and 3 spatial dimensions. The package has been employed for computing the chameleon field profiles in cosmic voids [61] and around halos [62].…”

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

“…Finally, there are the modified gravity models [8][9][10], which include terms that effectively act similarly to a varying CC. Models of particular interest are screened modified gravities, [11][12][13], like symmetron [14][15][16][17][18], and chameleon models [19][20][21][22][23][24][25][26][27].…”