Search results for "COSMOLOGY"
showing 10 items of 2905 documents
Kontsevich and Takhtajan construction of star product on the Poisson Lie group GL(2)
2001
Comparing the star product defined by Takhtajan on the Poisson-Lie group GL(2) and any star product calculated from the Kontsevich's graphs (any ''K-star product'') on the same group, we show, by direct computation, that the Takhtajan star product on GL(2) can't be written as a K-star product.
Monopolium production from photon fusion at the Large Hadron Collider
2008
6 pages, 6 figures.-- PACS nrs.: 14.80.Hv; 95.30.Cq; 98.70.-f; 98.80.-k.-- Printed version published Aug 2009.-- ArXiv pre-print available at: http://arxiv.org/abs/0809.0272
Cosmologie des théories de gravite modifiées
2017
The study of physical cosmology has reached an exciting era. For the first time in human history, a quantitative model for the formation and the evolution of the Universe exists, which explains a wide range of phenomena and has been tested with incredible accuracy during the last century. Moreover, weare approaching a time when a bounty of high quality cosmological data will be available,allowing us to use cosmology as a tool to test fundamental physics.In particular, as the large-scale structures of the Universe are governed by gravity, cosmology can help us to asses the correctness of Albert Einstein’s general relativity. This idea fueledmost of the work described in this manuscript,in wh…
The INTEGRAL/SPI response and the Crab observations
2004
The Crab region was observed several times by INTEGRAL for calibration purposes. This paper aims at underlining the systematic interactions between (i) observations of this reference source, (ii) in-flight calibration of the instrumental response and (iii) the development and validation of the analysis tools of the SPI spectrometer. It first describes the way the response is produced and how studies of the Crab spectrum lead to improvements and corrections in the initial response. Then, we present the tools which were developed to extract spectra from the SPI observation data and finally a Crab spectrum obtained with one of these methods, to show the agreement with previous experiments. We …
ECLAIRs: A microsatellite for the prompt optical and X-ray emission of Gamma-Ray Bursts
2001
The prompt gamma-ray emission of Gamma-Ray Bursts (GRBs) is currently interpreted in terms of radiation from electrons accelerated in internal shocks in a relativistic fireball. On the other hand, the origin of the prompt (and early afterglow) optical and X-ray emission is still debated, mostly because very few data exist for comparison with theoretical predictions. It is however commonly agreed that this emission hides important clues on the GRB physics and can be used to constrain the fireball parameters, the acceleration and emission processes and to probe the surroundings of the GRBs. ECLAIRs is a microsatellite devoted to the observation of the prompt optical and X-ray emission of GRBs…
Results from the ULTRA experiment in the framework of the EUSO project
2005
The detection of Cerenkov light from EAS in a delayed coincidence with fluorescence light gives a strong signature to discriminate protons and neutrinos in cosmic rays. For this purpose, the ULTRA experiment has been designed with 2 detectors: a small EAS array (ETscope) and an UV optical device including wide field (Belenos) and narrow field (UVscope) Cerenkov light detectors. The array measures the shower size and the arrival direction of the incoming EAS, while the UV devices, pointing both to zenith and nadir, are used to determine the amount of direct and diffused coincident Cerenkov light. This information, provided for different diffusing surfaces, will be used to verify the possibil…
Detection of the Cherenkov light diffused by sea water with the ULTRA experiment
2007
The study of Ultra High Energy Cosmic Rays represents one of the most challenging topic in the Cosmic Rays and in the Astroparticle Physics fields. The interaction of primary particles with atmospheric nuclei produces a huge Extensive Air Shower together with isotropic emission of UV fluorescence light and highly directional Cherenkov photons, that are reflected/diffused isotropically by the impact on the Earth's surface or on high optical depth clouds. For space-based observations, detecting the reflected Cherenkov signal in a delayed coincidence with the fluorescence light improves the accuracy of the shower reconstruction in space and in particular the measurement of the shower maximum, …
Requirements and simulation study of the performance of EUSO as external payload on board the international space station
2005
The "Extreme Universe Space Observatory - EUSO" has been conceived as the first Space mission devoted to the investigation of Ultra High Energy Cosmic Ray, using the Earth's atmosphere as a giant detector. The scientific objectives of the experiment are to observe the UHECR spectrum above the GZK energy, with an improvement of one order of magnitude in the statistics of collected events with respect to the existing experiments, in such a way to study the source distribution in a full sky survey, as well as to open the channel (set a confidence limit) on the neutrino astronomy in this energy range. Supposed to be accommodated as external payload on board the International Space Station, EUSO…
The Deep Rho Ophiuchi XMM-Newton Observation (DROXO)
2005
International audience; We present the X-ray data and the analysis status of the DROXO (Deep Rho Oph XMM-Newton Observation) project, aimed to mainly characterize the spectro-variability properties of YSOs in the nearby and very young ρ Oph star forming region. We focus on a few selected initial scientific results for few interesting YSOs, such as Elias 29 and YLW16A. In Elias 29 we see the 6.4 keV fluorescent Fe line as already reported in literature, whereas in YLW16A we do not detect the fluorescent line at odd with previous findings. Hence we conclude that the line intensity does change with time (and/or physical conditions).
Bounds on the density of sources of ultra-high energy cosmic rays from the Pierre Auger Observatory
2013
We derive lower bounds on the density of sources of ultra-high energy cosmic rays from the lack of significant clustering in the arrival directions of the highest energy events detected at the Pierre Auger Observatory. The density of uniformly distributed sources of equal intrinsic intensity was found to be larger than similar to (0.06 – 5) x 10(-4) Mpc(-3) at 95% CL, depending on the magnitude of the magnetic defections. Similar bounds, in the range (0.2 – 7) x 10(-4) Mpc(-3), were obtained for sources following the local matter distribution.