SÉMINAIRE DU GRECO
"Equivalence Between the Covariant and Bardeen Perturbation Formalisms" 

Sandro Dias Pinto Vitenti 

It is often argued in the literature that one of the main advantages of the covariant approach to describe the cosmological perturbations is that the Bardeen formalism is coordinate dependent. Here we discuss the relations between these two approaches and reformulate the Bardeen approach in a completely covariant manner. For that, we introduce the notion of pure and mixed tensors that yields an adequate language to treat both perturbative approaches in a common framework. Additionally, we define full nonlinear tensors that at first order correspond to the two known gauge invariant variables $\Phi$ and $\Psi$. We also stress that in the referred covariant approach one necessarily introduces an additional hypersurface choice to the problem, which in the case of a Friedmann background metric, has degrees of freedom similar to the gauge transformations.


lundi 9 décembre 2013  11:00 Salle des séminaires François Arago, Institut d'Astrophysique de Paris 
