Kinetic field theory for cosmic structure formation

Abstract

We apply kinetic field theory to non-linear cosmic structure formation. Kinetic field theory decomposes the cosmic density field into particles and follows their trajectories through phase space. We assume that initial particle momenta are drawn from a Gaussian random field. We place particular emphasis on the late-time, asymptotic behaviour on small spatial scales of low-order statistical measures for the distribution of particles in configuration and velocity space. Our main result is that the power spectra for density and velocity fluctuations in ensembles of particles freely streaming along Zel’dovich trajectories asymptotically fall off with wave number k like $$k^{-3}$$ k - 3 for $$k\rightarrow \infty $$ k → ∞ , irrespective of the cosmological model and the type of dark matter assumed, with the exponent set only by the number of spatial dimensions. This conclusion remains valid for density-fluctuation power spectra if particle interactions are taken into account in a mean-field approximation. We also show that the bispectrum of freely streaming particles falls off asymptotically like $$k^{-11/2}$$ k - 11 / 2 under the same general conditions.

Kinetic field theory: generic effects of alternative gravity theories on non-linear cosmic density-fluctuations

“…Kinetic field theory (KFT) is a statistical theory for the evolution of classical particle ensembles in or out of equilibrium [11,[14][15][16]. It defines an initial state of the ensemble by the probability distribution for phase-space positions x (i) to be occupied.…”