Initial conditions for cosmological N-body simulations of the scalar sector of theories of Newtonian, Relativistic and Modified Gravity

Abstract

We present a description for setting initial particle displacements and field values for simulations of arbitrary metric theories of gravity, for perfect and imperfect fluids with arbitrary characteristics. We extend the Zel'dovich Approximation to nontrivial theories of gravity, and show how scale dependence implies curved particle paths, even in the entirely linear regime of perturbations. For a viable choice of Effective Field Theory of Modified Gravity, initial conditions set at high redshifts are affected at the level of up to 5% at Mpc scales, which exemplifies the importance of going beyond Λ-Cold Dark Matter initial conditions for modifications of gravity outside of the quasi-static approximation. In addition, we show initial conditions for a simulation where a scalar modification of gravity is modelled in a Lagrangian particle-like description. Our description paves the way for simulations and mock galaxy catalogs under theories of gravity beyond the standard model, crucial for progress towards precision tests of gravity and cosmology.

27 pages, 6 figure, code available at http://falconb.org. Matches version published in JCAP

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• Initial Conditions for Accurate N-Body Simulations of Massive Neutrino Cosmologies
• hi_class: Background Evolution, Initial Conditions and Approximation Schemes
• Efficient simulations of large scale structure in modified gravity cosmologies with comoving Lagrangian acceleration
• Relativistic Interpretation of Newtonian Simulations for Cosmic Structure Formation
• A parametrisation of modified gravity on nonlinear cosmological scales
• GRAMSES: a new route to general relativistic $N$-body simulations in cosmology. Part I. Methodology and code description
• Relativistic initial conditions for N-body simulations
• Beyond the growth rate of cosmic structure: Testing modified gravity models with an extra degree of freedom
• Second-order cosmological perturbation theory and initial conditions for $N$-body simulations