Publications (4)0 Total impact
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ABSTRACT: We present a new approach to computing the matter density power spectrum,
from large linear scales to small highly nonlinear scales. Instead of
explicitly computing a partial series of high-order diagrams, as in
perturbative resummation schemes, we embed the standard perturbation theory
within a realistic nonlinear Lagrangian-space ansatz. We also point out that an
"adhesion-like" regularization of the shell-crossing regime is more realistic
than a "Zel'dovich-like" behavior, where particles freely escape to infinity.
This provides a "cosmic web" power spectrum with good small-scale properties
that provide a good matching with a halo model on mildly nonlinear scales. We
obtain a good agreement with numerical simulations on large scales, better than
3% for $k\leq 1 h$Mpc$^{-1}$, and on small scales, better than 10% for $k \leq
10 h$Mpc$^{-1}$, at $z \geq 0.35$, which improves over previous methods.
02/2013;
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ABSTRACT: We investigate the performance of an analytic model of the 3D matter
distribution, which combines perturbation theory with halo models, for
weak-lensing configuration-space statistics. We compared our predictions for
the weak-lensing convergence two-point and three-point correlation functions
with numerical simulations and fitting formulas proposed in previous works. We
also considered the second- and third-order moments of the smoothed convergence
and of the aperture-mass. As in our previous study of Fourier-space
weak-lensing statistics, we find that our model agrees better with simulations
than previously published fitting formulas. Moreover, we recover the dependence
on cosmology of these weak-lensing statistics and we can describe multi-scale
moments. This approach allows us to obtain the quantitative relationship
between these integrated weak-lensing statistics and the various contributions
to the underlying 3D density fluctuations, decomposed over perturbative,
two-halo, or one-halo terms.
12/2011;
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ABSTRACT: We investigate how unified models should be built to be able to predict the
matter-density bispectrum (and power spectrum) from very large to small scales
and that are at the same time consistent with perturbation theory at low $k$
and with halo models at high $k$. We use a Lagrangian framework to decompose
the bispectrum into "3-halo", "2-halo", and "1-halo" contributions, related to
"perturbative" and "non-perturbative" terms. We describe a simple
implementation of this approach and present a detailed comparison with
numerical simulations. We show that the 1-halo and 2-halo contributions contain
counterterms that ensure their decay at low $k$, as required by physical
constraints, and allow a better match to simulations. Contrary to the power
spectrum, the standard 1-loop perturbation theory can be used for the
perturbative 3-halo contribution because it does not grow too fast at high $k$.
Moreover, it is much simpler and more accurate than two resummation schemes
investigated in this paper. We obtain a good agreement with numerical
simulations on both large and small scales, but the transition scales are
poorly described by the simplest implementation. This cannot be amended by
simple modifications to the halo parameters, but we show how it can be
corrected for the power spectrum and the bispectrum through a simple
interpolation scheme that is restricted to this intermediate regime. Then, we
reach an accuracy on the order of 10% on mildly and highly nonlinear scales,
while an accuracy on the order of 1% is obtained on larger weakly nonlinear
scales. This also holds for the real-space two-point correlation function.
02/2011;
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ABSTRACT: We investigate the building of unified models that can predict the
matter-density power spectrum and the two-point correlation function from very
large to small scales, being consistent with perturbation theory at low $k$ and
with halo models at high $k$. We use a Lagrangian framework to re-interpret the
halo model and to decompose the power spectrum into "2-halo" and "1-halo"
contributions, related to "perturbative" and "non-perturbative" terms. We
describe a simple implementation of this model and present a detailed
comparison with numerical simulations, from $k \sim 0.02$ up to $100
h$Mpc$^{-1}$, and from $x \sim 0.02$ up to $150 h^{-1}$Mpc. We show that the
1-halo contribution contains a counterterm that ensures a $k^2$ tail at low $k$
and is important not to spoil the predictions on the scales probed by baryon
acoustic oscillations, $k \sim 0.02$ to $0.3 h$Mpc$^{-1}$. On the other hand,
we show that standard perturbation theory is inadequate for the 2-halo
contribution, because higher order terms grow too fast at high $k$, so that
resummation schemes must be used. We describe a simple implementation, based on
a 1-loop "direct steepest-descent" resummation for the 2-halo contribution that
allows fast numerical computations, and we check that we obtain a good match to
simulations at low and high $k$. Our simple implementation already fares better
than standard 1-loop perturbation theory on large scales and simple fits to the
power spectrum at high $k$, with a typical accuracy of 1% on large scales and
10% on small scales. We obtain similar results for the two-point correlation
function. However, there remains room for improvement on the transition scale
between the 2-halo and 1-halo contributions, which may be the most difficult
regime to describe.
09/2010;
