Next ACϟJC: 3 March, 2015 2pm, Cyril Pitrou

Post date: Feb 26, 2015 12:23:53 AM

Title: xPand: An algorithm for perturbing homogeneous cosmologies

Abstract: In the context of cosmological perturbations, the main aspects of large scale structure dynamics is understood by linearization of equations of General Relativity (GR) around a background cosmological solution. Indeed, it enables to compute the power spectrum of fluctuations in the metric and the matter. However, the intrinsic non-linear features of GR are lost with this approximation and it can be necessary to rely on higher order perturbations when dealing with higher order statistics due to mode-mode coupling. Since the derivation of the equations themselves can be very involved, we developed a new method to obtain systematically a perturbative expansion when the background spacetime is homogeneous but not necessarily isotropic, encompassing most cosmological backgrounds. Based on geometrical methods, and implemented in a computer algebra system (xAct), this package named 'xPand' allows to obtain very efficiently the equations which rule the non-linear dynamics, thus avoiding the long and tedious computations generally associated with such expansions.

Discussion Leader: Cyril Pitrou (Institut d'Astrophysique de Paris)