1,375 research outputs found
Transients from Zel'dovich initial conditions
We investigate the error implied by the use of the Zel'dovich approximation
to set up the initial conditions at a finite redshift zi in numerical
simulations. Using a steepest-descent method developed in a previous work we
derive the probability distribution P(delta_R) of the density contrast in the
quasi-linear regime. This also provides its dependence on the redshift zi at
which the simulation is started. Thus, we find that the discrepancy with the
exact pdf (defined by the limit zi->infinity) is negligible after the scale
factor has grown by a factor a/a_i>5, for scales which were initially within
the linear regime with sigma_i>0.1. This shows that the use of the Zel'dovich
approximation to implement the initial conditions is sufficient for practical
purposes since these are not very severe constraints.Comment: 6 pages, final version published in A&
Explicit computation of shear three-point correlation functions: the one-halo model case
We present a method for calculating explicit expressions of the shear
three-point function for various cosmological models. The method is applied
here to the one-halo model in case of power law density profiles for which
results are detailed. The three-point functions are found to reproduce to a
large extent patterns in the shear correlations obtained in numerical
simulations and may serve as a guideline to implement optimized methods for
detecting the shear three-point function. In principle, the general method
presented here can also be applied for other models of matter correlation.Comment: 8 pages, 6 figures, submitted to A
Dynamics of gravitational clustering II. Steepest-descent method for the quasi-linear regime
We develop a non-perturbative method to derive the probability distribution
of the density contrast within spherical cells in the
quasi-linear regime. Indeed, since this corresponds to a rare-event limit a
steepest-descent approximation can yield asymptotically exact results. We check
that this is the case for Gaussian initial density fluctuations, where we
recover most of the results obtained by perturbative methods from a
hydrodynamical description. Moreover, we correct an error which was introduced
in previous works for the high-density tail of the pdf. This feature, which
appears for power-spectra with a slope , points out the limitations of
perturbative approaches which cannot describe the pdf for
\delta_R \ga 3 even in the limit . This break-up does not
involve shell-crossing and it is naturally explained within our framework.
Thus, our approach provides a rigorous treatment of the quasi-linear regime,
which does not rely on the hydrodynamical approximation for the equations of
motion. Besides, it is actually simpler and more intuitive than previous
methods. Our approach can also be applied to non-Gaussian initial conditions.Comment: 18 pages, final version published in A&
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
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