Fluctuation primordiale de densité

En cosmologie, les fluctuations primordiales de densité sont les variations de densité qui furent présentes au commencement de l'histoire de l'univers à l'époque du Big Bang, et qui sont à l'origine de la structure de l'univers actuel. Dans le modèle de l'inflation cosmique, ces variations trouvent leur origine dans les fluctuations quantiques présentes durant l'ère de Planck. Elles ont grandi et sont devenues des fluctuations classiques par la suite en accompagnant l'expansion rapide qu'a connue l'univers à ce stade. Il est généralement admis que l'univers observable était en équilibre thermodynamique avant cette expansion et que sans ces fluctuations l'univers aurait été parfaitement homogène, et que les galaxies et les amas de galaxies ne se seraient pas formés. Les observations du fond diffus cosmologique et du décalage vers le rouge sont utilisées pour mesurer la distribution passée et présente de la matière et du rayonnement. Grâce à ces observations, des caractéristiques impo

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Neutrino masses and cosmology with Lyman-alpha forest power spectrum

Arnaud Borde, Julien Lesgourgues

We present constraints on neutrino masses, the primordial fluctuation spectrum from inflation, and other parameters of the ACDM model, using the one-dimensional Ly alpha-forest power spectrum measured by [1] from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III), complemented by Planck 2015 cosmic microwave background (CMB) data and other cosmological probes. This paper improves on the previous analysis by [2] by using a more powerful set of calibrating hydrodynamical simulations that reduces uncertainties associated with resolution and box size, by adopting a more flexible set of nuisance parameters for describing the evolution of the intergalactic medium, by including additional freedom to account for systematic uncertainties, and by using Planck 2015 constraints in place of Planck 2013. Fitting Ly alpha data alone leads to cosmological parameters in excellent agreement with the values derived independently from CMB data, except for a weak tension on the scalar index n(s). Combining BOSS Ly alpha with Planck CMB constrains the sum of neutrino masses to Sigma m(nu) < 0.12 eV (95% C.L.) including all identified systematic uncertainties, tighter than our previous limit (0.15 eV) and more robust. Adding Ly alpha data to CMB data reduces the uncertainties on the optical depth to reionization tau, through the correlation of tau with sigma(8). Similarly, correlations between cosmological parameters help in constraining the tensor-toscalar ratio of primordial fluctuations r. The tension on n(s) can be accommodated by allowing for a running dn(s)/d In k. Allowing running as a free parameter in the fits does not change the limit on Sigma m(nu). We discuss possible interpretations of these results in the context of slow-roll inflation.

Iop Publishing Ltd2015

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Standard Model Higgs boson mass from inflation

Amaury Magnin

We analyse one-loop radiative corrections to the inflationary potential in the theory, where inflation is driven by the Standard Model Higgs field. We show that inflation is possible provided the Higgs mass mH lies in the interval mmin < mH < mmax, where mmin = [136.7 + (mt - 171.2) × 1.95] GeV, mmax = [184.5 + (mt - 171.2) × 0.5] GeV and mt is the mass of the top quark. In the renormalization scheme associated with the Einstein frame the predictions of the spectral index of scalar fluctuations and of the tensor-to-scalar ratio practically do not depend on the Higgs mass within the admitted region and are equal to ns = 0.97 and r = 0.0034 correspondingly. © 2009.

2009

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Hybrid inflation in the complex plane

Valerie Fiona Domcke, Kohei Kamada

Supersymmetric hybrid inflation is an exquisite framework to connect inflationary cosmology to particle physics at the scale of grand unification. Ending in a phase transition associated with spontaneous symmetry breaking, it can naturally explain the generation of entropy, matter and dark matter. Coupling F-term hybrid inflation to soft supersymmetry breaking distorts the rotational invariance in the complex inflaton plane - an important fact, which has been neglected in all previous studies. Based on the delta N formalism, we analyze the cosmological perturbations for the first time in the full two-field model, also taking into account the fast-roll dynamics at and after the end of inflation. As a consequence of the two-field nature of hybrid inflation, the predictions for the primordial fluctuations depend not only on the parameters of the Lagrangian, but are eventually fixed by the choice of the inflationary trajectory. Recognizing hybrid inflation as a two-field model resolves two shortcomings often times attributed to it: the fine-tuning problem of the initial conditions is greatly relaxed and a spectral index in accordance with the PLANCK data can be achieved in a large part of the parameter space without the aid of supergravity corrections. Our analysis can be easily generalized to other (including large-field) scenarios of inflation in which soft supersymmetry breaking transforms an initially single-field model into a multi-field model.

Iop Publishing Ltd2014

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Big Bang

Le Big Bang (« Grand Boum ») est un modèle cosmologique utilisé par les scientifiques pour décrire l'origine et l'évolution de l'Univers. De façon générale, le terme « Big Bang » est associé à toute

Inflation cosmique

vignette |upright=1.5 |Inflation cosmique (en beige), avant seconde. L'inflation cosmique est un modèle cosmologique s'insérant dans le paradigme du Big Bang lors duquel une région de l'Univers compr

Fond diffus cosmologique

Le fond diffus cosmologique (FDC, ou CMB pour l'anglais cosmic microwave background, « fond cosmique de micro-ondes ») est un rayonnement électromagnétique très homogène observé dans toutes les direc

PHYS-402: Astrophysics IV : observational cosmology

Cosmology is the study of the structure and evolution of the universe as a whole. This course describes the principal themes of cosmology, as seen from the point of view of observations.

PHYS-427: Relativity and cosmology I

Introduce the students to general relativity and its classical tests.

MSE-421: Statistical mechanics

This course presents an introduction to statistical mechanics geared towards materials scientists. The concepts of macroscopic thermodynamics will be related to a microscopic picture and a statistical interpretation. Lectures and exercises will be complemented with hands-on simulation projects.