35 research outputs found
Minkowski Functionals of Convergence Maps and the Lensing Figure of Merit
Minkowski functionals (MFs) quantify the topological properties of a given
field probing its departure from Gaussianity. We investigate their use on
lensing convergence maps in order to see whether they can provide further
insights on the underlying cosmology with respect to the standard second-order
statistics, i.e., cosmic shear tomography. To this end, we first present a
method to match theoretical predictions with measured MFs taking care of the
shape noise, imperfections in the map reconstruction, and inaccurate
description of the nonlinearities in the matter power spectrum and bispectrum.
We validate this method against simulated maps reconstructed from shear fields
generated by the MICE simulation. We then perform a Fisher matrix analysis to
forecast the accuracy on cosmological parameters from a joint MFs and shear
tomography analysis. It turns out that MFs are indeed helpful to break the
-- degeneracy thus generating a sort of chain
reaction leading to an overall increase of the Figure of Merit.Comment: 16 pages, 5 figures. Matches published version in PR
Unveiling the Dynamics of the Universe
We explore the dynamics and evolution of the Universe at early and late
times, focusing on both dark energy and extended gravity models and their
astrophysical and cosmological consequences. Modified theories of gravity not
only provide an alternative explanation for the recent expansion history of the
universe, but they also offer a paradigm fundamentally distinct from the
simplest dark energy models of cosmic acceleration. In this review, we perform
a detailed theoretical and phenomenological analysis of different modified
gravity models and investigate their consistency. We also consider the
cosmological implications of well motivated physical models of the early
universe with a particular emphasis on inflation and topological defects.
Astrophysical and cosmological tests over a wide range of scales, from the
solar system to the observable horizon, severely restrict the allowed models of
the Universe. Here, we review several observational probes -- including
gravitational lensing, galaxy clusters, cosmic microwave background temperature
and polarization, supernova and baryon acoustic oscillations measurements --
and their relevance in constraining our cosmological description of the
Universe.Comment: 94 pages, 14 figures. Review paper accepted for publication in a
Special Issue of Symmetry. "Symmetry: Feature Papers 2016". V2: Matches
published version, now 79 pages (new format
Generalized observers and velocity measurements in General Relativity
To resolve some unphysical interpretations related to velocity measurements
by static observers, we discuss the use of generalized observer sets, give a
prescription for defining the speed of test particles relative to those
observers and show that, for any locally inertial frame, the speed of a freely
falling material particle is always less than the speed of light at the
Schwarzschild black hole surface.Comment: 20 pages, 1 figure, submitted to General Relativity and Gravitatio
Sources of contamination to weak lensing tomography: redshift-dependent shear measurement bias
The current methods available to estimate gravitational shear from
astronomical images of galaxies introduce systematic errors which can affect
the accuracy of weak lensing cosmological constraints. We study the impact of
KSB shape measurement bias on the cosmological interpretation of tomographic
two-point weak lensing shear statistics.
We use a set of realistic image simulations produced by the STEP
collaboration to derive shape measurement bias as a function of redshift. We
define biased two-point weak lensing statistics and perform a likelihood
analysis for two fiducial surveys. We present a derivation of the covariance
matrix for tomography in real space and a fitting formula to calibrate it for
non-Gaussianity.
We find the biased aperture mass dispersion is reduced by ~20% at redshift
~1, and has a shallower scaling with redshift. This effect, if ignored in data
analyses, biases sigma_8 and w_0 estimates by a few percent. The power of
tomography is significantly reduced when marginalising over a range of
realistic shape measurement biases. For a CFHTLS-Wide-like survey, [Omega_m,
sigma_8] confidence regions are degraded by a factor of 2, whereas for a
KIDS-like survey the factor is 3.5. Our results are strictly valid only for KSB
methods but they demonstrate the need to marginalise over a redshift-dependent
shape measurement bias in all future cosmological analyses.Comment: 13 pages, 8 figures. Submitted MNRA