Periodic Report Summary 3 - THEMODS (Theories and Models of the Dark Sector: Dark Matter, Dark Energy and Gravity.) The TheMoDS team aims to test theories of Dark Matter, Dark Energy and Gravity with cosmological and solar-system observations. By using a generalized model of Dark Matter, the team has investigated its possible cosmological observational signatures and proceeded to test it using data from ESA’s Planck satellite which measured small fluctuations in the Cosmic Microwave Background, a relic radiation permeating the Universe. Assuming that deviations from the plain Cold Dark Matter model are constant in time and space, the team determined that there is no observational evidence for such generalized models. Further investigation into non-constant deviations is in progress and this will enable the project researchers to track the properties of Dark Matter through cosmic time. The team has developed and used a novel parametric framework for testing gravity with cosmology. This framework is used for testing whether certain features in the Cosmic Microwave Background are due to the presence of Dark Matter and Dark Energy or due to new gravitational degrees of freedom. Further and more accurate modelling of Dark Matter is necessary in order to extract all available information about gravity and Dark Energy from cosmological observations. Thus the team has also investigated techniques for solving the Vlasov equation as an alternative to N-body simulations for calculating the Cold Dark Matter non-linear power spectrum. Many proposed theories of gravity provide mechanisms whereby the gravitational field can “morph” when a threshold in its strength is reached. This presents difficulties in testing such theories with data. The team developed a new framework for testing such gravitational theories both with solar system observations that reside on one side of this threshold, and with cosmological observations that reside on the other.
