Horndeski Gravity as an Effective Dark Energy Fluid in Cosmological N-body Simulations
Abstract
Unraveling the nature of the cosmic expansion, driven by Dark Energy (DE), remains one of the key challenges in modern cosmology. Modified Gravity (MG) models provide an alternative to the standard cosmological constant paradigm. These models predict distinct signatures in the growth of structure, yet analytical predictions are challenging due to the highly non--linear equations involved. To overcome this problem, we study MG as an effective DE fluid. To this end, we have incorporated linear DE perturbations into the N--body code CONCEPT, which relies on the Einstein--Boltzmann solver CLASS. We replaced the CLASS version used by CONCEPT with mochi_CLASS, a patched version that includes Horndeski family models. By writing linear DE perturbations (δρDE, δPDE, θDE, and σDE) in terms of metric perturbations in the synchronous gauge, the N--body code is able to evolve the effective fluid using the Boltzmann equation. Our current simulations encompass a range of cosmological scenarios ---w0waCDM, Hu--Sawicki f(R) and cubic Galileon--- each extended to include massive neutrinos. For each of the models, we have found deviations from General Relativity close to what is predicted in the linear regime: a sub-0.2% relative difference for ΛCDM, up to 40% for f(R) and a sub-25% for cubic Galileon. Since our code is the first to implement Horndeski gravity into an N--body code, its validation is a non--trivial computational task. Our novel code opens the door to explore a vast number of modified gravity models in the context of current and future cosmological surveys.
Related
- Barrow Holographic Dark Energy with a Ricci Cutoff in Power-Law f(Q,Lm) Gravity: Late-Time Cosmological Dynamics
- Linear perturbation theory and structure formation in a Horndeski theory of gravity without dark matter
- Constraints on Horndeski gravity with phantom crossing
- Constraints on Horndeski gravity with phantom crossing
- Nonreciprocal black holes with primary hair in beyond Horndeski gravity: Exact solutions and stability
BibTeX
@misc{aballay2026horndeski,
title = {{Horndeski Gravity as an Effective Dark Energy Fluid in Cosmological N-body Simulations}},
author = {Vicente Pedreros Aballay},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.06330},
eprint = {2611.06330},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.06330},
}
RIS
TY - UNPB
TI - Horndeski Gravity as an Effective Dark Energy Fluid in Cosmological N-body Simulations
AU - Vicente Pedreros Aballay
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2611.06330
UR - https://arxiv.org/abs/2611.06330
AB - Unraveling the nature of the cosmic expansion, driven by Dark Energy (DE), remains one of the key challenges in modern cosmology. Modified Gravity (MG) models provide an alternative to the standard cosmological constant paradigm. These models predict distinct signatures in the growth of structure, yet analytical predictions are challenging due to the highly non--linear equations involved. To overcome this problem, we study MG as an effective DE fluid. To this end, we have incorporated linear DE perturbations into the N--body code CONCEPT, which relies on the Einstein--Boltzmann solver CLASS. We replaced the CLASS version used by CONCEPT with mochi_CLASS, a patched version that includes Horndeski family models. By writing linear DE perturbations (δρ_DE, δP_DE, θ_DE, and σ_DE) in terms of metric perturbations in the synchronous gauge, the N--body code is able to evolve the effective fluid using the Boltzmann equation. Our current simulations encompass a range of cosmological scenarios ---w_0w_aCDM, Hu--Sawicki f(R) and cubic Galileon--- each extended to include massive neutrinos. For each of the models, we have found deviations from General Relativity close to what is predicted in the linear regime: a sub-0.2% relative difference for ΛCDM, up to 40% for f(R) and a sub-25% for cubic Galileon. Since our code is the first to implement Horndeski gravity into an N--body code, its validation is a non--trivial computational task. Our novel code opens the door to explore a vast number of modified gravity models in the context of current and future cosmological surveys.
ER -