Proca-stinated Cosmology II: Matter, Halo, and Lensing Statistics in the vector Galileon

TL;DR

This paper investigates the cubic vector Galileon model, a modified gravity theory, analyzing its effects on large-scale structure formation and lensing to identify potential observational constraints.

Contribution

It provides a comprehensive nonlinear analysis of the cubic vector Galileon model using N-body simulations, highlighting its unique phenomenology and observational signatures.

Findings

Fifth force significantly affects velocity fields and lensing potential at late times.

Redshift-space distortions and weak lensing are promising probes for testing the model.

The model offers an alternative explanation for cosmic acceleration and H_0 tension.

Abstract

The generalised Proca (GP) theory is a modified gravity model in which the acceleration of the cosmic expansion rate can be explained by self interactions of a cosmological vector field. In this paper we study a particular sub-class of the GP theory, with up to cubic order Lagrangian, known as the cubic vector Galileon (cvG) model. This model is similar to the cubic scalar Galileon (csG) in many aspects, including a fifth force and the Vainshtein screening mechanism, but with the additional flexibility that the strength of the fifth force depends on an extra parameter -- interpolating between zero and the full strength of the csG model -- while the background expansion history is independent of this parameter. It offers an interesting alternative to LambdaCDM in explaining the cosmic acceleration, as well as a solution to the tension between early- and late-time measurements of the Hubble constant H_0. To identify the best ways to test this model, in this paper we conduct a comprehensive study of the phenomenology of this model in the nonlinear regime of large-scale structure formation, using a suite of N-body simulations run with the modified gravity code ECOSMOG. By inspecting thirteen statistics of the dark matter field, dark matter haloes and weak lensing maps, we find that the fifth force in this model can have particularly significant effects on the large-scale velocity field and lensing potential at late times, which suggest that redshift-space distortions and weak lensing can place strong constraints on it.