Kinetic field theory: effects of modified gravity theories with screening mechanisms on non-linear cosmic density fluctuations

Abstract

In a mean-field approximation within Kinetic Field Theory, it is possible to derive an accurate analytic expression for the power spectrum of present-day non-linear cosmic density fluctuations. It depends on the theory of gravity and the cosmological model via the expansion function of the background space-time, the growth factor derived from it, and the gravitational coupling strength, which may deviate from Newton's constant in a manner depending on time and spatial scale. In earlier work [1], we introduced a functional Taylor expansion around general relativity and the cosmological standard model to derive the effects of a wide class of modified-gravity theories on the non-linear power spectrum, assuming that such effects need to be small given the general success of the standard model. Here, we extend this class towards theories with small-scale screening, modeling screening effects by a suitably flexible interpolating function. We compare the Taylor expansion with full mean-field solutions and find good agreement where expected. We find typical relative enhancements of the non-linear power spectrum between a few and a few ten per cent in a broad range of wave numbers between $k\gtrsim 0.1-10h{\mathrm{Mpc}}^{-1}$, in good qualitative agreement with results of numerical simulations. Taking nDGP gravity as a quantitative example we compare our results to N-body simulations and find percent-level agreement for wavenumbers $k\lesssim 2h{\text{Mpc}}^{-1}$, if the scale where screening sets in, $k^{\ast }$, is adapted appropriately. This extends the application of our analytic approach to non-linear cosmic structure formation to essentially all classes of modified-gravity theories.

Accepted for publication in JCAP. v2: Added some clarifying remarks and moved some calculations from Sect. 5 to a new appendix

References in corpus (9)

• Ghosts in the self-accelerating universe
• Constructing stabilized brane world models in five-dimensional Brans-Dicke theory
• Non-linear interactions in a cosmological background in the DGP braneworld
• A parametrisation of modified gravity on nonlinear cosmological scales
• Trajectories of point particles in cosmology and the Zel'dovich approximation
• Non-equilibrium statistical field theory for classical particles: Basic kinetic theory
• Kinetic Field Theory for Cosmic Structure Formation
• Kinetic Field Theory: Perturbation theory beyond first order
• Kinetic field theory: generic effects of alternative gravity theories on non-linear cosmic density-fluctuations