Individual halo bias in models of f(R) gravity

¹ Departamento de Física, Universidad de Córdoba, E-14071 Córdoba, Spain
² Departamento de Física, Universidad Técnica Federico Santa María, Avenida Vicuña Mackenna 3939, San Joaquín, Santiago, Chile
³ Instituto de Astrofísica de Canarias, s/n, E-38205 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain

^⋆ Corresponding author: jorge.farieta@uco.es

Received: 3 April 2025
Accepted: 11 July 2025

Abstract

Context. Halo bias links the statistical properties of the spatial distribution of dark matter (DM) halos to those of the underlying DM field, providing insights into clustering properties in both general relativity (GR) and modified-gravity such as f(R) models. While the primary halo mass-dependent bias has been studied in detailed, the secondary bias, which accounts for the additional dependencies on other internal halo properties, can offer a sensitive probe for testing gravity beyond the Λ-cold dark matter (ΛCDM) model.

Aims. The aim of this study is to quantify any potential deviations between ΛCDM and f(R) gravity models in halo clustering, at both the primary and secondary level, as well as in the distributions of halo properties in the cosmic web.

Methods. Using N-body simulations of f(R) gravity models, we assessed the scaling relations and the primary and secondary bias signals of halo populations on the basis of a halo-by-halo estimator of large-scale effective bias. Our analysis was performed using halo number density as the independent variable.

Results. The relative difference in the effective bias between the f(R) models and ΛCDM is sensitive, albeit slightly, to the power index of modified gravity. The largest deviations from GR are measured for low-mass halos, where the average bias at a fixed number density decreases by up to 5% for fixed scaling indices. We also show that the scaling relations for some environmental properties, including neighbour statistics, Mach number, and local overdensity, exhibit small but non-negligible deviations (3–5%) from GR for a wide range of number densities. Our results suggest that the properties of halos in sheets and voids show the largest departures from GR (> 10% in some cases). In terms of secondary bias, we do not find any statistically significant deviations with respect to ΛCDM for any of the properties explored in this work.