Cosmological simulations with hydrodynamics of screened scalar-tensor gravity with non-universal coupling

Abstract

Aims. We study the effects of letting dark matter and gas in the Universe couple to the scalar field of the symmetron model, a modified gravity theory, with varying coupling strength. We also search for a way to distinguish between universal and non-universal couplings in observations. Methods. The research is performed utilising a series of hydrodynamic, cosmological N-Body simulations, studying the resulting power spectra and galaxy halo properties, such as density and temperature profiles. Results. In the cases of universal couplings, the deviations in the baryon fraction from ΛCDM are smaller than in the cases of nonuniversal couplings throughout the halos. The same is apparent in the power spectrum baryon bias, defined as the ratio of gas to dark matter power spectrum. Deviations of the density profiles and power spectra from the ΛCDM reference values can differ significantly between dark matter and gas because the dark matter deviations are mostly larger than the deviations in the gas.

Mass-temperature relation in ΛCDM and modified gravity

“…[74] modified the ISIS code [80] and ran two sets of simulations, one for f (R)-gravity models and another one for the symmetron models, both containing 256 3 DM particles. The box size and background cosmology were different for the two models, due to consistency with previous works of the authors [87]. In the case of the f (R) gravity (symmetron) the DM particle mass was 3×10 10 M /h (8.32×10 10 M /h), Ω Λ = 0.727, Ω CDM = 0.227 and Ω b = 0.045 (Ω Λ = 0.65, Ω CDM = 0.3 and Ω b = 0.05), and the box size 200 Mpc h −1 (256 Mpc h −1 ), with h = 0.7 (h = 0.65).…”

The BAHAMAS project: the CMB–large-scale structure tension and the roles of massive neutrinos and galaxy formation

“…The introduction of baryons and associated processes will further weaken the link between halo properties and cosmology. 10 Some proposed modified theories of gravity and 'interacting' dark energy models invoke non-universal couplings, such that the fifth force couples differently with dark matter than it does with baryons (e.g., Hammami & Mota 2015). In this case it is possible to affect the baryon fractions of collapsed systems without invoking feedback, but it is far from clear that such models would be able to naturally account for the observed trend of gas fraction with halo mass, which approximately converges to the universal baryon fraction, Ω b /Ωm, for the most massive clusters (see Fig.4) boxes necessary for the LSS tests without changing any aspect of the subgrid physics (feedback or otherwise).…”

Modeling void abundance in modified gravity

“…on regions of large density or deep potentials [3]. Examples include fðRÞ models with the chameleon mechanism [4][5][6][7][8][9], braneworld models which display the Vainshtein mechanism [10][11][12], and the symmetron model with a symmetry breaking of the scalar potential [13][14][15][16]. Most viable models of cosmic acceleration via modified gravity are nearly indistinguishable at the background level and may be quite degenerate, even when considering linear perturbation effects.…”

“…Investigating the nonlinear regime of modified gravity models requires N-body simulations [15,, in which one must solve nonlinear equations for the extra scalar field in order to properly account for screening mechanisms. From simulations one may extract the matter power spectrum on linear and nonlinear scales [18,20,21,23,30,39,40] as well as properties of dark matter halos, such as their abundance [19][20][21]27,30,39,41,42], bias [19,25,27,30] and profiles [19,20,27,43].…”