Talk detail

Participant	van der Walt, Peet
Institution	Rhodes University - Lucas Avenue - Grahamstown - Eastern Cape - South Africa

Session	TC3	Accepted		Order	Time
Talk	Oral abstract	Title	Modelling the past null cone using characteristic numerical relativity
Co-authors
Abstract	The characteristic formalism (CF) of numerical relativity is based on a system of coordinates aligned with outgoing null cones. These coordinates were designed for studying gravitational waves, but can easily be adapted to model cosmological past null cones (PNCs). Similar to observational coordinates, this provides a model that only makes use of information causally connected to an observer at the cone vertex. However, the diameter distance as a radial coordinate, is not a unique measure of distance beyond the PNC refocusing. This limits the model’s application to the region prior to the apparent horizon (AH). We address this problem by introducing a metric based on the Bondi-Sachs metric where the radial coordinate is replaced by an affine parameter. A model was derived from this metric and it is shown how an existing numerical scheme can be adapted for simulation of the PNC beyond the AH. Numerical calculations on this model were found to have the same stability and convergence properties as the standard CF. A particularly interesting application of this model is to evaluate the historical evolution of different models where observations appear to be similar on the current PNC, e.g. evolving $\Lambda$CDM observations as a Lemaitre-Tolman-Bondi model.