Blanc SIMI 5 - Blanc - SIMI 5 - Physique subatomique et théories associées, astrophysique, astronomie et planétologie

The Large-Scale Structure of the Universe at Next-to-Leanding Order – COSMO@NLO

The development of instabilities generated in any cosmological fluid by gravity on a large scale leads to the structuring of the universe as we see it today: galaxies, clusters of galaxies, embedded in a large-scale cosmological network. The development of these instabilities results from a competition between the expansion of the universe, which limits its scope, and the forces of gravitation. The details of the large-scale distribution of matter that is observed then depends both on the way in which the expansion of the universe takes place, on its content in matter, and of course on any modification of the laws of the gravitation.

The implementation of advanced theoretical methods, such as perturbation theory, for the analysis of such a system consisting of self-gravitating cosmological fluids in an expanding univers then makes it possible to identify observables (correlation functions, power spectra, etc.) to make quantitative predictions on these to effectively constrain these models.

The results we obtained enabled us to make important advances in several directions: unveiling consistency relations between observables, identifying new classes of modified gravity models and exploring their observational consequences, developing methods of systematic calculations of density spectra in perturbation theory or the development of new observables.

Our current short term objectives are,

- The calculation of spectra for cosmic shear and redshift space distorsion observations;
- The extension of the calculation to cosmologies with massive neutrinos;
- The development of alternative statistical indicators (topological invariants, density profiles).

It is not less than 43 publications that have been made. One of the major results of the project was the production of public codes for calculating the NNLO spectrum (next to next to leading order calculations),
or calculation of probability distribution function of local densities, LSSFast,
that we illustrate here.

Submission summary

The mechanisms that drive the development of gravitational instabilities, leading to the formation of the large-scale structure of the universe, is not yet understood in its full details. Yet, with the arrival of a new generation of projects of observational cosmology, such as the LSST and EUCLID, that aim at measuring dark energy properties from large-scale structure observations, it is now necessary to characterize its properties with a large precision and in a controlled manner. N-body simulations bring answers to those issues but only for a very limited number of models and for a limited range of cosmological parameters. The scientific cases of the project aforementioned rely however heavily on our ability to make such predictions for large classes of models. It is therefore necessary to sharpen our theoretical knowledge on the growth of gravitational structures.
This project aims at developing tools for predicting and computing cosmic density spectra and bispectra (three-point correlation function) for a large set of cosmological models that include non-standard effects such as massive neutrinos or clustering dark energy. More precisely we wish to build theoretical tools for predicting those quantities analytically and with a controlled precision in the quasilinear regime - therefore in a regime that defines the validity of the linear regime and extends it - and develop robust and fast numerical codes for computing a set of well defined observables such as those related to cosmic shear observations, redshift space density field, etc. We also wish to construct more phenomenological models that explore the relationships between the density field (and its various components) and the halo density.
The approaches we favor in this project make use of computation techniques that have been recently put forward in which re-summations of large classes of diagrams can be taken into account. These approaches explicitly, or implicitly, take advantage of the so-called eikonal approximation. Those approaches allow to develop perturbation theory calculations in a controlled way and for a large class of observables such as spectra, bispectra etc. Our project aims at writing and releasing packages - in fortran to make its portability to different systems easier - for the fast computation of perturbation theory spectra and bispectra beyond linear theory. More precisely, we wish to develop codes that compute spectra up to 2 loops (NNLO) and bispectra up to 1 loop (NLO).

Project coordination

Francis BERNARDEAU (Institut de Physique Théorique, CEA Saclay) –

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


IPhT Institut de Physique Théorique, CEA Saclay

Help of the ANR 343,672 euros
Beginning and duration of the scientific project: December 2012 - 48 Months

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