Limits on decaying dark energy density models from the CMB temperature-redshift relation

The nature of the dark energy is still a mystery and several models have been proposed to explain it. Here we consider a phenomenological model for dark energy decay into photons and particles as proposed by Lima (Phys Rev D 54:2571, 1996). He studied the thermodynamic aspects of decaying dark energy models in particular in the case of a continuous photon creation and/or disruption. Following his approach, we derive a temperature redshift relation for the cosmic microwave background (CMB) which depends on the effective equation of state w eff and on the "adiabatic index” γ. Comparing our relation with the data on the CMB temperature as a function of the redshift obtained from Sunyaev-Zel'dovich observations and at higher redshift from quasar absorption line spectra, we find w eff=−0.97 ± 0.03, adopting for the adiabatic index γ=4/3, in good agreement with current estimates and still compatible with w eff=−1, implying that the dark energy content being constant in tim

The Sunyaev-Zeldovich MITO Project

Compton scattering of the cosmic microwave background radiation by electrons in the hot gas in clusters of galaxies - the Sunyaev-Zeldovich effect - has long been recognized as a uniquely important feature, rich in cosmological and astrophysical information. We briefly describe the effect, and emphasize the need for detailed S-Z and X-ray measurements of nearby clusters in order to use the effect as a precise cosmological probe. This is the goal of the MITO project, whose first stage consisted of observations of the S-Z effect in the Coma cluster. We report the results of these observations.Comment: To appear in Proceedings of `Understanding our Universe at the close of XXth century', School held Apr 25 - May 6 2000, Cargese, 16 pages LaTeX, 2 figures ps (using elsart.sty & elsart.cls), text minor revisio

MITO measurements of the Sunyaev-Zeldovich Effect in the Coma cluster of galaxies

We have measured the Sunyaev-Zeldovich effect towards the Coma cluster (A1656) with the MITO experiment, a 2.6-m telescope equipped with a 4-channel 17 arcminute (FWHM) photometer. Measurements at frequency bands 143+/-15, 214+/-15, 272+/-16 and 353+/-13 GHz, were made during 120 drift scans of Coma. We describe the observations and data analysis that involved extraction of the S-Z signal by employing a spatial and spectral de-correlation scheme to remove a dominant atmospheric component. The deduced values of the thermal S-Z effect in the first three bands are DT_{0} = -179+/-38,-33+/-81,170+/-35 microKelvin in the cluster center. The corresponding optical depth, tau=(4.1+/-0.9) 10^{-3}, is consistent (within errors) with both the value from a previous low frequency S-Z measurement, and the value predicted from the X-ray deduced gas parameters.Comment: Ap.J.Letters accepted, 4 pages, 2 figure

Limits on decaying dark energy density models from the CMB temperature-redshift relation

The nature of the dark energy is still a mystery and several models have been proposed to explain it. Here we consider a phenomenological model for dark energy decay into photons and particles as proposed by Lima (J. Lima, Phys. Rev. D 54, 2571 (1996)). He studied the thermodynamic aspects of decaying dark energy models in particular in the case of a continuous photon creation and/or disruption. Following his approach, we derive a temperature redshift relation for the CMB which depends on the effective equation of state $w_{eff}$ and on the "adiabatic index" $\gamma$. Comparing our relation with the data on the CMB temperature as a function of the redshift obtained from Sunyaev-Zel'dovich observations and at higher redshift from quasar absorption line spectra, we find $w_{eff}=-0.97 \pm 0.034$, adopting for the adiabatic index $\gamma=4/3$, in good agreement with current estimates and still compatible with $w_{eff}=-1$, implying that the dark energy content being constant in time.Comment: 8 pages, 1 figur

From nuclei to atoms and molecules: the chemical history of the early Universe

The "dark age" of the Universe is generally pointed out as the period between the recombination epoch and the horizon of current observations (z=5-6). The arrow of time in the cosmic history describes the progression from simplicity to complexity, because the present Universe is clumpy and complicated unlike the homogeneous early Universe. Thus it is crucial to know the nature of the constituents, in order to understand the conditions of the formation of the first bound objects. In this paper we analyse the chemical history of this "dark age" through the creation of the primordial nuclei to the formation of the first atoms and molecules. Then we will describe the consequences of the molecular formation on the birth of the proto-objects. In this context we will mention the important works of Dennis W. Sciama who influenced a large number of theorists -cosmologists and astronomers- on this new field of research dedicated to primordial molecules.Comment: 25 pages, 1 figure, Special Issue dedicated to Pr. Dennis W. Sciam

The Rome Paris collaboration

International audienceSince the first "Twinning CEE Project" between the Group of Francesco Mechiorri and our Laboratory at Observatoire de Paris and Ecole Normale Supérieure, and then through several European Networks and NASA Collaborations on the Cosmic Microwave Background, a long-term and fruitful cooperation has existed between Rome and Paris. This contribution will focus on the human story, the principal results and the possible prospects of this wonderful collaboration

Cosmic microwave background and first molecules in the early universe

International audienceBesides the Hubble expansion of the universe, the main evidence in favor of the big-bang theory was the discovery, by Penzias and Wilson, of the cosmic microwave background (hereafter CMB) radiation. In 1990, the COBE satellite (Cosmic Background Explorer) revealed an accurate black-body behavior with a temperature around 2.7 K. Although the microwave background is very smooth, the COBE satellite did detect small variations—at the level of one part in 100 000—in the temperature of the CMB from place to place in the sky. These ripples are caused by acoustic oscillations in the primordial plasma. While COBE was only sensitive to long-wavelength waves, the Wilkinson Microwave Anisotropy Probe (WMAP)—with its much higher resolution—reveals that the CMB temperature variations follow the distinctive pattern predicted by cosmological theory. Moreover, the existence of the microwave background allows cosmologists to deduce the conditions present in the early stages of the big bang and, in particular, helps to account for the chemistry of the universe. This report summarizes the latest measurements and studies of the CMB with the new calculations about the formation of primordial molecules. The PLANCK mission—planned to be launched in 2009—is also presented

L'espace et le temps : le point de vue astronomique

Schatzman Evry, Signore Monique. L'espace et le temps : le point de vue astronomique. In: Communications, 41, 1985. L'espace perdu et le temps retrouvé, sous la direction de Rémy Lestienne et Edgar Morin. pp. 81-94