Skip to content

Engineering topics

Casarini, Luciano

Publications and source records attributed to Casarini, Luciano.

5 records

All sources NASA NTRS DOE OSTI

DOE OSTI2018

Cosmology and fundamental physics with the Euclid satellite

Euclid is a European Space Agency medium-class mission selected for launch in 2020 within the cosmic vision 2015–2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and red-shifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid’s Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Linear and non-linear perturbations in dark energy models

In this work we discuss observational aspects of three time-dependent parameterisations of the dark energy equation of state w ( z ). In order to determine the dynamics associated with these models, we calculate their background evolution and perturbations in a scalar field representation. After performing a complete treatment of linear perturbations, we also show that the non-linear contribution of the selected w ( z ) parameterisations to the matter power spectra is almost the same for all scales, with no significant difference from the predictions of the standard ΛCDM model.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Sample variance in N-body simulations and impact on tomographic shear predictions

We study the effects of sample variance in N-body simulations as a function of the size of the simulation box, namely in connection with predictions on tomographic shear spectra. We make use of a set of eight ΛCDM simulations in boxes of 128, 256, and 512 h{sup −1} Mpc a side, for a total of 24, differing just by the initial seeds. Among the simulations with 128 and 512 h{sup −1} Mpc a side, we suitably select those closest and farthest from average. Numerical and linear spectra P(k,z) are suitably connected at low k to evaluate the effects of sample variance on shear spectra C{sub ij}(ℓ) for 5 or 10 tomographic bands. We find that shear spectra obtained by using 128 h{sup −1} Mpc simulations can vary up to ∼25%, just because of the seed. The sample variance lowers to ∼3.3% when using 512 h{sup −1} Mpc. These percentages could however slightly vary if other sets of the same number of realizations were considered. Accordingly, in order to match the ∼1% precision expected for the data, if still using eight boxes, we require a size of ∼1300–1700 h{sup −1} Mpc for them.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

Direct recovery of fluctuation spectra from tomographic shear spectra

Forthcoming experiments will enable us to determine high precision tomographic shear spectra. Matter density fluctuation spectra, at various z, should then be recovered from them, in order to constrain the model and determine the DE state equation. Available analytical expressions, however, do the opposite, enabling us to derive shear spectra from fluctuation spectra. Here we find the inverse expression, yielding density fluctuation spectra from observational tomographic shear spectra. The procedure involves SVD techniques for matrix inversion. We show in detail how the approach works and provide a few examples.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Non-linear weak lensing forecasts

We investigate the impact of non-linear corrections on dark energy parameter estimation from weak lensing probes. We find that using halofit expressions, suited to ΛCDM models, implies substantial discrepancies with respect to results directly obtained from N-body simulations, when w(z)≠−1. Discrepancies appear strong when using models with w'(z = 0) > 0, as fiducial models; they are however significant even in the neighborhood of ΛCDM, where neglecting the degrees of freedom associated with the DE state equation can lead to a misestimate of the matter density parameter Ω{sub m}.

79 ASTRONOMY AND ASTROPHYSICS↗