Julien Lesgourgues

Cette personne n’est plus à l’EPFL

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Publications associées (71)

The Cosmic Linear Anisotropy Solving System (CLASS). Part II: Approximation schemes

Julien Lesgourgues, Diego Blas Temino

Boltzmann codes are used extensively by several groups for constraining cosmological parameters with Cosmic Microwave Background and Large Scale Structure data. This activity is computationally expensive, since a typical project requires from 104 to 105 Bo ...

2011

Dark goo: bulk viscosity as an alternative to dark energy

Jean-Sébastien Gagnon, Julien Lesgourgues

We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an "effective" pressure containing the ...

2011

The Cosmic Linear Anisotropy Solving System (CLASS) IV: efficient implementation of non-cold relics

Julien Lesgourgues

We present a new flexible, fast and accurate way to implement massive neutrinos, warm dark matter and any other non-cold dark matter relics in Boltzmann codes. For whatever analytical or numerical form of the phase-space distribution function, the optimal ...

2011

Perturbation Theory Of The Cosmological Log-Density Field

Julien Lesgourgues, Xin Wang

The matter density field exhibits a nearly lognormal probability density distribution after entering into the nonlinear regime. Recently, it has been shown that the shape of the power spectrum of a logarithmically transformed density field is very close to ...

2011

Single-field inflation constraints from CMB and SDSS data

Julien Lesgourgues, Fabio Finelli, Jan Hamann

We present constraints on canonical single-field inflation derived from WMAP five year, ACBAR, QUAD, BICEP data combined with the halo power spectrum from SDSS LRG7. Models with a non-scale-invariant spectrum and a red tilt n(S) < 1 are now preferred over ...

2010

Cosmological parameters from large scale structure - geometric versus shape information

Julien Lesgourgues, Jan Hamann

The matter power spectrum as derived from large scale structure (LSS) surveys contains two important and distinct pieces of information: an overall smooth shape and the imprint of baryon acoustic oscillations (BAO). We investigate the separate impact of th ...

2010

Dark energy with non-adiabatic sound speed: initial conditions and detectability

Julien Lesgourgues

Assuming that the universe contains a dark energy fluid with a constant linear equation of state and a constant sound speed, we study the prospects of detecting dark energy perturbations using CMB data from Planck, cross-correlated with galaxy distribution ...

2010

Model independent constraints on mass-varying neutrino scenarios

Julien Lesgourgues

Models of dark energy in which neutrinos interact with the scalar field supposed to be responsible for the acceleration of the Universe usually imply a variation of the neutrino masses on cosmological time scales. In this work we propose a parametrization ...

American Physical Society2009

Optimising Boltzmann codes for the PLANCK era

Julien Lesgourgues, Jan Hamann

High precision measurements of the Cosmic Microwave Background (CMB) anisotropies, as can be expected from the PLANCK satellite, will require high-accuracy theoretical predictions as well. One possible source of theoretical uncertainty is the numerical err ...

2009

Cosmological constraints on a light nonthermal sterile neutrino

Julien Lesgourgues

Although the MiniBooNE experiment has severely restricted the possible existence of light sterile neutrinos, a few anomalies persist in oscillation data, and the possibility of extra light species contributing as a subdominant hot (or warm) component is st ...

American Physical Society2009

Lyman-alpha constraints on warm and on warm-plus-cold dark matter models

Alexey Boyarsky, Oleg Ruchayskiy, Julien Lesgourgues

We revisit Lyman-alpha bounds on the dark matter mass in Lambda Warm Dark Matter (Lambda-WDM) models, and derive new bounds in the case of mixed Cold plus Warm models (Lambda-CWDM), using a set up which is a good approximation for several theoretically wel ...

2008

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