Halo models in modified gravity theories with self-accelerated expansion

TL;DR

This paper examines how different modified gravity theories affect the structure of dark matter halos, highlighting the impact of effective gravity suppression or enhancement and the observational challenges due to the Vainshtein mechanism.

Contribution

It provides a comparative analysis of halo structures in sDGP and galileon models using solutions of the Boltzmann equation, emphasizing the effects of modified gravity on halo density profiles.

Findings

Halo density is larger in sDGP and smaller in galileon models compared to Newtonian gravity.

Differences between models are only observable outside the halo due to the Vainshtein mechanism.

Modified gravity effects are suppressed or enhanced at large distances, affecting halo structure.

Abstract

We investigate the structure of halos in the sDGP (self-accelerating branch of the Dvali-Gavadadze-Porrati braneworld gravity) model and the galileon modified gravity model on the basis of the static and spherically symmetric solutions of the collisionless Boltzmann equation, which reduce to the singular isothermal sphere model and the King model in the limit of Newtonian gravity. The common feature of these halos is that the density of a halo in the outer region is larger (smaller) in the sDGP (galileon) model, respectively, in comparison with Newtonian gravity. This comes from the suppression (enhancement) of the effective gravity at large distance in the sDGP (galileon) model, respectively. However, the difference between these modified gravity models and Newtonian gravity only appears outside the halo due to the Vainshtein mechanism, which makes it difficult to distinguish between them. We also discuss the case in which the halo density profile is fixed independently of the gravity model for comparison between our results and previous work.