Mode coupling evolution in arbitrary inflationary backgrounds

The evolution of high order correlation functions of a test scalar field in arbitrary inflationary backgrounds is computed. Whenever possible, exact results are derived from quantum field theory calculations. Taking advantage of the fact that such calculations can be mapped, for super-horizon scales, into those of a classical system, we express the expected correlation functions in terms of classical quantities, power spectra, Green functions, that can be easily computed in the long-wavelength limit. Explicit results are presented that extend those already known for a de Sitter background. In particular the expressions of the late time amplitude of bispectrum and trispectrum, as well as the whole high-order correlation structure, are given in terms of the expansion factor behavior. When compared to the case of a de Sitter background, power law inflation and chaotic inflation induced by a massive field are found to induce high order correlation functions the amplitudes of which are amplified by almost one order of magnitude. These results indicate that the dependence of the related non-Gaussian parameters - such as f_NL - on the wave-modes is at percent level.Comment: 22 pages, 5 figures. Revised version with correction of typos and more detailed discussions on the validity regime of the calculation

Constraints on higher-dimensional gravity from the cosmic shear three-point correlation function

With the developments of large galaxy surveys or cosmic shear surveys it is now possible to map the dark matter distribution at truly cosmological scales. Detailed examinations of the statistical properties of the dark matter distribution reveal the detail of the large-scale structure growth of the Universe. In particular it is shown here that the behavior of the density field bi-spectrum is sensitive to departure from normal gravity in a way which depends only weakly on the background evolution. The cosmic shear bispectrum appears to be particularly sensitive to changes in the Poisson equation: we show that the current cosmic shear data can already be used to infer constraints on the scale of a possible higher-dimensional gravity, above 2 h^{-1}Mpc.Comment: 5 pages, 3 figures, submitted to PR

Cosmological Perturbation Theory for streams of relativistic particles

Motion equations describing streams of relativistic particles and their properties are explored in detail in the framework of Cosmological Perturbation Theory. Those equations, derived in any metric both in the linear and nonlinear regimes, express the matter and momentum conservation. In this context we extend the setup of adiabatic initial conditions - that was initially performed in the Conformal Newtonian gauge - to the Synchronous gauge. The subhorizon limit of the nonlinear motion equations written in a generic perturbed Friedmann-Lema\^{i}tre metric is then derived and analyzed. We show in particular that the momentum field $P_{i}(x)$ is always potential in the linear regime and remains so at subhorizon scales in the nonlinear regime. Finally the equivalence principle is exploited to highlight invariance properties satisfied by such a system of equations, extending that known for streams of non-relativistic particles, namely the extended Galilean invariance

Describing massive neutrinos in cosmology as a collection of independent flows

A new analytical approach allowing to account for massive neutrinos in the non-linear description of the growth of the large-scale structure of the universe is proposed. Unlike the standard approach in which neutrinos are described as a unique hot fluid, it is shown that the overall neutrino fluid can be equivalently decomposed into a collection of independent flows. Starting either from elementary conservation equations or from the evolution equation of the phase-space distribution function, we derive the two non-linear motion equations that each of these flows satisfies. Those fluid equations describe the evolution of macroscopic fields. We explain in detail the connection between the collection of flows we defined and the standard massive neutrino fluid. Then, in the particular case of adiabatic initial conditions, we explicitly check that, at linear order, the resolution of this new system of equations reproduces the results obtained in the standard approach based on the collisionless Boltzmann hierarchy. Besides, the approach advocated in this paper allows to show how each neutrino flow settles into the cold dark matter flow depending on initial velocities. It opens the way to a fully non-linear treatment of the dynamical evolution of neutrinos in the framework of large-scale structure growth.Comment: 23 pages, 4 figure

On the importance of nonlinear couplings in large-scale neutrino streams

We propose a procedure to evaluate the impact of nonlinear couplings on the evolution of massive neutrino streams in the context of large-scale structure growth. Such streams can be described by general nonlinear conservation equations, derived from a multiple-flow perspective, which generalize the conservation equations of non-relativistic pressureless fluids. The relevance of the nonlinear couplings is quantified with the help of the eikonal approximation applied to the subhorizon limit of this system. It highlights the role played by the relative displacements of different cosmic streams and it specifies, for each flow, the spatial scales at which the growth of structure is affected by nonlinear couplings. We found that, at redshift zero, such couplings can be significant for wavenumbers as small as $k=0.2\,h$/Mpc for most of the neutrino streams.Comment: 12 pages, 1 figur

Cosmic Strings Lens Phenomenology Revisited

We present investigations of lens phenomenological properties of cosmic strings for deep galaxy surveys. General results that have obtained for lineic energy distribution are presented first. We stress that generically the local convergence always vanishes in presence of strings although there might be some significant distortions. We then propose a simplified model of strings, we call ``Poisson strings'', for which exhaustive investigations can be done either numerically or analytically.Comment: 6 pages; To appear in the Proceedings of the XXth Moriond Astrophysics Meeting "Cosmological Physics with Gravitational Lensing", eds. J.-P. Kneib, Y. Mellier, M. Moniez and J. Tran Thanh Van, Les Arcs, France, March 11th-18th 200