Nathalie Deruelle

Matching conditions for cosmological perturbations.

We derive the matching conditions for cosmological perturbations in a Friedmann Universe where the equation of state undergoes a sharp jump, for instance as a result of a phase transition. The physics of the transition which is needed to follow the fate of the perturbations is clarified. We dissipate misleading statements made recently in the literature concerning the predictions of the primordial fluctuations from inflation and confirm standard results. Applications to string cosmology are considered.

Long wavelength iteration of Einstein's equations near a spacetime singularity.

We clarify the links between a recently developped long wavelength iteration scheme of Einsteins equations, the Belinski Khalatnikov Lifchitz (BKL) general solution near a singularity and the antinewtonian scheme of Tomitas. We determine the regimes when the long wavelength or antinewtonian scheme is directly applicable and show how it can otherwise be implemented to yield the BKL oscillatory approach to a spacetime singularity. When directly applicable we obtain the generic solution of the scheme at first iteration (third order in the gradients) for matter a perfect fluid. Specializing to spherical symmetry for simplicity and to clarify gauge issues, we then show how the metric behaves near a singularity when gradient effects are taken into account.

Perturbations of brane worlds

We consider cosmological models where the universe, governed by Einsteins equations, is a piece of a five dimensional double-sided antichar21{}de Sitter spacetime (that is, a

Linearized gravity in the Randall-Sundrum scenario

``{Z}_{2}ensuremath{-}mathrm{s}mathrm{y}mathrm{m}mathrm{m}mathrm{e}mathrm{t}mathrm{r}mathrm{i}mathrm{c}phantom{rule{0ex}{0ex}}mathrm{b}mathrm{u}mathrm{l}mathrm{k}mathrm{})

Conservation laws and cosmological perturbations in curved universes

with matter confined to its four dimensional Robertson-Walker boundary or ``brane. We study the perturbations of such models. We use conformally Minkowskian coordinates to disentangle the contributions of the bulk gravitons and of the motion of the brane. We find the restrictions put on the bulk gravitons when matter on the brane is taken to be a scalar field and we solve in this case the brane perturbation equations.

REMARKS ON THE MYERS-PERRY AND EINSTEIN–GAUSS–BONNET ROTATING SOLUTIONS

In the literature about the Randall-Sundrum scenario, one finds, on the one hand, that there exist (small) corrections to Newtons law of gravity on the brane and, on the other, that the exact (and henceforth linearized) Einstein equations can be recovered on the brane. The explanation for these seemingly contradictory results is that the behavior of the bulk far from the brane is different in both models. We show that explicitly in this paper.

Topological defects and cosmic microwave background anisotropies: Are the predictions reliable ?

When working in synchronous gauges, pseudo-tensor conservation laws are often used to set the initial conditions for cosmological scalar perturbations, when those are generated by topological defects which suddenly appear in an up to then perfectly homogeneous and isotropic universe. However those conservation laws are restricted to spatially flat

Two-body problem in scalar-tensor theories as a deformation of general relativity: An effective-one-body approach

(K=0)

Integral constraints on cosmological perturbations and their energy

Friedmann-Lema^{i}tre spacetimes. In this paper, we first show that in fact they implement a matching condition between the pre- and post-transition eras and, in doing so, we are able to generalize them and set the initial conditions for all

The Growth of density fluctuations in a simplified model of extended inflation

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