STRUCTURE FORMATION BY FIFTH FORCE: POWER SPECTRUM FROM N-BODY SIMULATIONS

We lay out the framework to numerically study nonlinear structure formation in the context of scalar-field-coupled cold dark matter models (phi CDM models) where the scalar field phi serves as dynamical dark energy. Adopting parameters for the scalar field that leave negligible effects on the cosmic microwave background (CMB) spectrum, we generate the initial conditions for our N-body simulations. The simulations follow the spatial distributions of dark matter and the scalar field, solving their equations of motion using a multilevel adaptive grid technique. We show that the spatial configuration of the scalar field depends sensitively on the local density field. The phi CDM model differs from standard Lambda CDM at small scales with observable modifications of, e. g., the mass function of halos as well as the matter power spectrum. Nevertheless, the predictions of both models for the Hubble expansion and the CMB spectrum are virtually indistinguishable. Hence, galaxy cluster counts and weak lensing observations, which probe structure formation at small scales, are needed to falsify this class of models.