Combined Effects of f(R) Gravity and Massive Neutrinos on the Turnaround Radii of Dark Matter Halos

Abstract

We present a new statistics based on the turnaround radii of cluster halos to break the dark sector degeneracy between the ΛCDM model and the alternative ones with f(R) gravity and massive neutrinos (ν) characterized by the strength of the fifth force, ∣f R0∣, and the total neutrino mass, M ν . Analyzing the Rockstar halo catalogs at the present epoch from the DUSTGRAIN-pathfinder N-body simulations performed for four different cosmologies, namely, ΛCDM (∣f R0∣ = 0, ∑m ν = 0.0 eV), fR6 (∣f R0∣ = 10−6, ∑m ν = 0.0 eV), fR6+0.06 eV(∣f R0∣ = 10−6, ∑m ν = 0.06 eV), and fR5+0.15 eV(∣f R0∣ = 10−5, ∑m ν = 0.15 eV), which are known to yield very similar conventional statistics to one another. For each model, we select those cluster halos that do not neighbor any other larger halos in their bound zones and construct their bound-zone peculiar velocity profiles at z = 0. Then, we determine the radial distance of each selected halo at which the bound-zone velocity becomes equal to the recession speed of the Hubble flow as its turnaround radius, and evaluate the cumulative probability distribution of the ratios of the turnaround radii to the virial counterparts, P(r t /r v ≥ α). The degeneracy between the fR6 and fR5+0.15 eV models is found to be readily broken by the 10σ ΔP difference in the value of P(α = 4), while the 3.2σ ΔP difference between the ΛCDM and fR6+0.06 eV models is detected in the value of P(α = 8.5). It is also found that the four models yield smaller differences in P(α) at higher redshifts.

Turnaround density evolution encodes cosmology in simulations

“…A hybrid of the two types of boundaries is the turnaround radius, which is a kinematically motivated boundary (the scale that separates a nonexpanding structure from the Hubble flow) that according to spherical collapse, also constitutes a scale of constant overdensity for collapsed structures of all masses at a given redshift. In recent years, the turnaround radius has gained considerable attention as a scale on which cosmological models can be tested (e.g., Pavlidou & Tomaras 2014; E-mail: gkorkidis@physics.uoc.gr Nojiri et al 2018;Capozziello et al 2019;Lopes et al 2019;Wong 2019;Pavlidou et al 2020;Santa Vélez & Enea Romano 2020;Del Popolo 2020;Faraoni et al 2020;Korkidis et al 2020;Lee & Baldi 2022). Pavlidou et al (2020) showed by employing the sphericalcollapse model that the matter density within the turnaround scale (the turnaround density, ρ ta ) could be used as a cosmologyprobing observable, with a number of attractive properties: For a given redshift, the turnaround density is universal and thus insensitive to halo size, selection biases, and sample completeness issues; its present-day value almost exclusively probes the matter density; and its evolution with redshift is sensitive to the dark energy content of the Universe.…”