Colloquium Paris VI de Cosmologie et Astroparticules


Le Colloquium de Cosmologie se tiendra une fois par mois sur le
campus de Jussieu le mercredi a 14 heures. Son objectif est de

présenter des séminaires pédagogiques d'interet général sur des
themes d'actualité en cosmologie et domaines connexes, aussi bien
théoriques qu'observationnels. Tous les chercheurs du campus Jussieu
sont les bienvenus ainsi que ceux des campus voisins: CdF, ENS,
IAP-Observatoire de Paris. Ce colloque est soutenu par la
Federation de Recherche Interactions Fondamentales

(les organisateurs: P. Astier, H. de Vega, P. Peter)

Années précédentes:   Année 2004-2005   Année 2005-2006  

Année 2006-2007

Octobre  2006

MERCREDI  25 octobre 2006, 14h00,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Kevork Abazajian (Univ. of Mariland)

             "Dark matter and  neutrino physics"

The nature of the dark matter is still unknown.
 Hidden in the neutrino sector of particle physics may be one or more
 fermions with no standard model interactions that nonetheless couple to neutrinos via their mass generation mechanism, namely sterile neutrinos.  Such a particle may be the dark matter, produced in the early universe
 through matter-suppressed neutrino mixing or matter-enhanced resonant
 mixing.  I will overview the kinetics of relativistic mixed neutrinos
 in dense environments, and will specify with sterile neutrino dark
 matter production in the early universe.  I will discuss how this
 candidate alters cosmological structure formation, and the resulting
 constraints from observed cosmological clustering.  In addition, I
 discuss how this candidate may be detected by X-ray telescopes.

  Novembre 2006

MERCREDI  15 novembre 2006, 14h00,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Rainer Beck (Max Planck & Univ. Bonn)

             "Cosmic Magnetism Revealed with the Square Kilometer Array (SKA)."

The origin of magnetic fields in stars, galaxies and clusters is an open problem in astrophysics and fundamental physics. "The Origin and Evolution of Cosmic Magnetism" is one of the Key Science Projects for the Square Kilometre Array (SKA), the international next-generation radio telescope.  An all-sky survey of Faraday rotation measures (RM) at 1.4 GHz will serve to model the structure and strength of the magnetic fields in the intergalactic medium, the interstellar medium of intervening galaxies and of the Milky Way.  Spectro-polarimetry will allow to separate RM components from distinct foreground and background regions and hence to perform 3-D "Faraday tomography" of the magnetized interstellar medium of the Milky Way and nearby galaxies.  Furthermore, polarization imaging with the SKA will open a new era in the observation of magnetic fields in galaxies, in galaxy clusters and in the intergalactic medium.

  Decembre 2006

MERCREDI  6 decembre 2006, 14h00,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Andreas Zech (LPNHE, Paris)

             "Observing the most energetic particles with the Pierre Auger Observatory"

The origin and nature of ultra-high energy cosmic rays is still an open question. Resolving this question is of  considerable importance for both astrophysics and particle physics. The Pierre Auger Observatory is the world's largest detector to study the high energy end of the cosmic ray spectrum.  It combines two observational techniques, an array of water Cherenkov detectors and four air fluorescence telescope stations, to observe the extensive air showers generated in the atmosphere by cosmic rays. This hybrid observation  mode yields an excellent resolution and allows for important systematic cross-checks. The Auger South site, located in the province of Mendoza in Argentina, has started data acquisition in 2004 with only  a small fraction of its full aperture. Since then it has been growing continuously and is now nearing its completion. The  collected data provide already some insights into the energy spectrum, the origin and composition of ultra-high energy cosmic rays. I will give an update of the status of the observatory and discuss our first scientific results.

  Janvier 2007

MERCREDI  17 janvier 2007, 14h00,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Peter L. Biermann (MPIfR Bonn et Tuscaloosa)

             "Origin and physics of the highest energy cosmic rays"

The highest energy cosmic ray particles are the most energetic particles known to us in the universe, and their observations have led us to build one of the largest detector system in the world, the AUGER air-shower array. We have detected particles to 3 10^{20} eV, which is a macroscopic energy.  There are a number of options how to generate them, and how to get these particles from their sources to us.  These particles may be accelerated to high energy in a shock wave, such as in a radio galaxy, or some other shock-wave such as during the formation of large scale structure in the universe. Other propositions assume that they are the product of a decay of a very massive particle (possibly connected to dark matter) and the merger of black holes. One key point will be to understand the cosmological web of magnetic fields, which may influence the propagation of high energy particles; here it is especially important to understand the role of a galactic wind and its magnetic structure.  I will discuss the observational and theoretical limits for an exemplary set of models, and also the predictions, that result from these models. I will place special emphasis on the search strategy that will be important once we will have statistically relevant AUGER data.  Detailed observations may allow us not only to set limits to the cosmic magnetic field, and the physics of sources, but also to aspects of particle physics.

  Fevrier 2007

MERCREDI  14 fevrier 2007, 14h00,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Liping Fu(IAP)

             "Cosmic shear from CFHTLS Wide"

A primary scientific goal of the Canada-France-Hawaii Telescope
Legacy Survey (CFHTLS) is the exploration of the dark matter power spectrum properties and its evolution with redshift using weak gravitational lensing (cosmic shear). I will present the current state of the cosmic shear
measurement using CFHTLS Wide 3rd release. It is the first time that the
cosmic shear signal is explored beyond the one degree scale, which will be
strong constraints on cosmological parameters. Meanwhile, the reliability
of the current shear measuring pipeline is checked using simulation data,
which shows high accuracy. In a short review, we compare our cosmic shear from CFTHLS with the other non-CFHTLS surveys showing a consistent signal.

  Mars 2007

MERCREDI  28 mars 2007, 14h00,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Patrick Valegeas (Saclay)

             "Formation of large-scale structures in the Universe: non-linear regime"

The large-scale structures we observe in the present universe
(such as galaxies and clusters of galaxies) have formed thanks to
gravitational instability which amplified the small density perturbations created in the early universe. Moreover, the power increases at small scales as in the CDM model which leads to a hierarchical scenario where small scales become non-linear first. Thus, at large scales or at early times (e.g. to study the CMB) one can use a perturbative approach. However, many observations (e.g weak-lensing) probe the weakly non-linear or highly non-linear regimes. This requires to go beyond the usual perturbative expansion.
After a brief review of the dynamics of gravitational clustering in the
cosmological context, I shall present various analytical methods which
have been devised to investigate the weakly non-linear regime.
In particular, I shall focus on recent systematic methods which amount
to reorganize the standard perturbative expansion by performing some
partial infinite resummations.

  Mai 2007

MERCREDI  23 mai 2007, 14h00,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Didier Barret  (CESR Toulouse)

             "General Relativistic Motion of Matter in regions of extremely strong
             gravity revealed through quasi-periodic oscillations by the X-ray Rossi

Kilo-Hz quasi-periodic oscillations (QPOs) have been discovered in
the X-ray flux of several low-mass accreting X-ray binaries. These
oscillations probe the motion of matter in a region of extreme
gravity, where fundamental predictions of strong field general
relativity, such as the existence of an innermost stable circular
orbit (ISCO), have yet to be tested. We have undertaken a systematic
analysis of the kilo-Hz quasi-periodic oscillations detected from
several sources by the Rossi X-ray Timing Explorer and observed in
several sources a reproducible effect that we interpret as the
signature of the ISCO. In this talk (intended for non specialists), I
will introduce kilo-Hz QPOs and review their general properties
before discussing their potential for strong gravity and dense
matter. I will then present the various pieces of evidence that we
have accumulated in favor of our recent claim that the sharp drop of
the coherence of the kilo-Hz QPOs at some critical frequency is
related to the ISCO.

Année 2005-2006

Septembre  2005

MERCREDI 14 SEPTEMBRE 2005, 14h00,  Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

             Ben Moore (University of Zurich)

             "Dark matter and structure formation in the Universe"

              The initial conditions for structure formation are now well constrained and
              we know that the Universe is dominated by dark energy and dark matter.
              However several key problems remain: astronomers have only identified
              and understood one percent of the Universe and we are unsure how the matter
              arranges itself into stars, planets and galaxies. Recent supercomputer calculations
              have allowed us to make substantial progress in these areas. I will discuss our
              quest to understand the nature of dark matter and to predict the distribution of cold
              dark matter from the scale of the lecture room to that of galaxies and clusters.

Octobre 2005

MERCREDI 12 OCTOBRE 2005, 14h00, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

            Ken Ganga (APC, Tolbiac)

             "Polarization of the Cosmic Microwave Background and the QUaD experiment"

            I will discuss the anisotropies in the cosmic microwave background (CMB) radiation,
            its polarization, and the goals we hope to achieve in measuring it. QUaD is an experiment
            for measuring the polariziation in the CMB from the South Pole. It uses similar technology
            as that successfully used by previous experiments such as BOOMERanG and which will
            be used by future experiments such as the Planck/HFI instrument. QUaD has taken data for
            the one season, and will continue operation for at least one more. Though no scientific results
            will be presented, I will review the goals of the experiment, give the status of the instrument,
            and will present our expectations and schedule.

Novembre 2005

MERCREDI 16 NOVEMBRE 2005, 14h00, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

            Jose Valle (IFC, Valencia)

             "Neutrinos yesterday, today and tomorrow"

            I briefly review the milestone events in the development of
            neutrino physics that culminated with the discovery of neutrino masses and
            the understanding of solar and atmospheric neutrino "anomalies". I
            highlight the role that reactors and accelerators have played in providing
            final confirmation of observations from underground experiments. I also
            discuss the issues of robustness of the oscillation interpretation, and
            the challenges for the next generation of experiments. Finally I discuss
            the significance of these findings towards the understanding of the
            ultimate origin of neutrino masses and mixings.

Decembre 2005

** MARDI**  6 DECEMBRE 2005, 14h00, Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Daniel Eisenstein (University of Arizona)
             "Dark Energy and Cosmic Sound"
             I present galaxy clustering results from the Sloan Digital Sky Survey that
             reveal the signature of acoustic oscillations of the photon-baryon fluid
             in the first million years of the Universe. The scale of this feature can be
             computed and hence the detection in the galaxy clustering serves as a standard
             ruler, giving a geometric distance to a redshift of 0.35. I will discuss the implications
             of this measurement for the composition of the universe, including dark energy and
             spatial curvature, and the prospects for future redshift surveys to use the acoustic peak
             to map the expansion history of the universe.             

Janvier 2006

  MERCREDI 18  JANVIER 2006, 14h00, Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Georg Raffelt (Max Planck Institute for Physics, Munich)
             "Neutrino Physics in Heaven"
              After an overview of the various themes that connect neutrino physics
              with astrophysics and cosmology I will focus on two main
              topics. First, what can we learn from the neutrino signal of a future
              galactic supernova, both about the neutrino mass ordering and about
              supernova physics. Second, what can we learn about neutrino
              properties from cosmological observables, notably about the neutrino
              absolute mass scale and about secret neutrino interactions from
              cosmological large-scale structure observables.

Fevrier 2006

  MERCREDI 22  FEVRIER 2006, **16h30**, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

            Helene Sol (LUTH, Meudon)
             "Astronomie gamma au sol : une nouvelle image du cosmos par l'experience europeenne HESS"

L'astronomie des très hautes énergies vient de franchir un cap décisif grâce aux performances  en sensibilité et résolution spatiale atteintes par l'expérience HESS, High Energy Stereoscopic System, pleinement opérationnelle depuis début 2004. Nous assistons maintenant à l'émergence d'une vision renouvelée de notre univers que le séminaire tentera d'illustrer, structurée autour de la physique des accélérateurs cosmiques tels que vents de pulsars, restes de supernovae, binaires-X et microquasars, sources galactiques non-identifiées - possibles accélérateurs 'sombres' - centre galactique, et noyaux actifs de galaxies.

Mars 2006

  MERCREDI 22 MARS 2006, 14h00, Salle des Seminaires, Sous-Sol, IAP, 98bis Boul Arago

            David Hogg (New York University)
             "Galaxies and galaxy merging in the last billion years"
I review what we know about the Local (nearest few hundred Mpc) Universe from studies of
             millions of galaxies with enormous surveys, such as the Sloan Digital Sky Survey. Structure in
             the Universe grows by merging and accretion, as do galaxies. I show that small-scale galaxy
             clustering measurements, galaxy morphology studies, and simple analyses of recent-past star-formation
             histories of galaxies can all put complementary constraints on the rate at which galaxies are
             accreting material and growing. These studies suggest that the galaxy population grows (in mass)
             by of order one percent per Gyr, with large variance among galaxies. I will focus on the observations
             and their interpretation, but there are also theoretical challenges. I am optimistic that in the future these
             kinds of observations will non-trivially constrain the dynamics of the dark matter on small scales.

Avril 2006

  MERCREDI 26 AVRIL 2006,  **16h30**, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

            Norma Sanchez (Observatoire de Paris, LERMA)
           "Trous Noirs dans l'Univers: naissance, vie, mort et rémanents des trous noirs"
Depuis quelques années, les trous noirs ne sont plus des objets purement théoriques mais sont
            devenus des objets physiques réels faisant partie de l'univers. Des observations astrophysiques
            des dernières annees (dans les domaines X, optique, infrarouge, gamma) ont produit une évidence
            grandissante de l'existence des trous noirs, en allant des trous noirs supermassifs dans les centres
            des galaxies, dont notre propre galaxie, aux trous noirs des masses stellaires, dont les systèmes
            binaires. Ces trous noirs sont décrits par la physique classique (non quantique), ils interagissent
            avec leur environment (étoiles, gaz, disques d'accrétion) produisant des effets observables. D'autre
            part, les trous noirs primordiaux ou microscopiques, bien qu'encore non d'etectés, sont l'objet
            d'un interet cosmologique et physique grandissant. Ce sont des trous noirs semiclassiques émettant
            par effet tunnel et la création des paires, des particules des toutes sortes avec un spectre thermique
            universel (émission de Hawking). Dans les dernières étapes de leur évaporation, les trous noirs
            deviennent purement quantiques, se transformant en cordes et se désintégrant en toutes sortes des
            particules avec une émission non thermique. Naissance, vie, fin de vie et rémanents des trous noirs
            dans tout leur rang des masses seront exposés.

Mai 2006

  MERCREDI 10 MAI 2006,  **16h30**, Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

             Olivier Doré (CITA, Toronto)
           "Mapping the polarized sky with WMAP: methods and cosmological implications"

            The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite
            designed to produce high resolution full sky maps of the temperature
            and polarization of the cosmic microwave background (CMB). The
            accurate characterization of the fluctuations in the CMB contains
            exquisite information about the global structure, composition, and
            evolution of the universe.

            Relying on the first three years of observations, WMAP has now
            measured these fluctuations with unprecedented accuracy. I will
            illustrate how a greater signal-to-noise in the temperature
            measurement but also a new large scale polarization signal detection
            have significantly sharpened our cosmological interpretation.

            A simple six-parameters cosmological model (flat LCDM); consisting of
            baryons, dark matter, a cosmological constant, initial perturbation
            spectrum amplitude and slope, and optical depth; is an excellent fit
            to the WMAP data, as well as a host of other astronomical experiments.

            The new WMAP data also hint at a small deviation from scale
             invariance in the primordial
             fluctuation power spectrum, a key prediction of inflation. If
             confirmed this would strengthen our confidence in the inflationary
             scenario and allow detailed model testing. Besides, the combination
             of WMAP data and other astronomical data places even stronger
             constraints on the density of dark matter and dark energy, the
             properties of neutrinos, the properties of dark energy and the
             geometry of the Universe

Juin 2006

  MERCREDI 21 JUIN 2006,  14h00, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

             Miguel Angel Aloy (MPI-Garching et Valencia)

            "Progenitors of Gamma Ray Bursts: theory and numerical simulations"

             I start by a summary of the current theoretical status and present
             observational data on Gamma Ray Bursts (GRB). I will put particular
             emphasis on the physical properties of the systems that can be
             progenitors of both short and long GRBs. Numerical simulations based
             on general relativitistic hydrodynamics have shown the physical realism of
             progenitor models as collapsars and mergers of neutron star binaries or neutron
             stars and black holes. These simulations provide quantitative estimates of generic
             properties of the relativistic outflows that can be compared with the available
             observational data and disentangle which progenitor models are best
             suited to reproduce the observed phenomenology.

Page web entretenue par Michael Joyce                                                           

Année 2004-2005

Septembre  2004

MERCREDI 29 SEPTEMBRE 2004, 14h30,  Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

Massimo Giovannini (CERN-TH)

                 "Magnetic fields in the early and in the present Universe"

              I shall review the present evidence of large-scale magnetic fields in
              galaxies, galaxy clusters and superclusters and I shall outline the
              main techniques used to infer the existence of cosmic magnetism. After
              discussing the problems related to the origin of large-scale magnetic fields,
              I shall focus on different suggestions emerging from field theory in curved
              space-times and from string theory arguing for a cosmological origin of
              large-scale magnetism. If magnetic fields were generated prior to the
              decoupling of photons from baryons, then, the thermodynamical history
              of the Universe may be modified already at the electroweak epoch.
              Direct experimental consequences can follow on the primary anisotropies of the
              Cosmic Microwave Background (CMB), on the polarization of the CMB
              itself (Faraday effect) and on the production of stochastic backgrounds of
              gravitational waves.

Octobre 2004

MERCREDI 20 OCTOBRE 2004, 14h00, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

            Eric Linder (LBL, Berkeley)

                 "Dark Energy and the Dynamics of the Universe"

              Discoveries in the last few years have revolutionized
              our knowledge of the universe and our ideas of its ultimate fate.
              Measurements of the expansion of the universe show that it is not
              slowing down under normal gravity but accelerating due to an unknown,
              gravitationally repulsive "dark energy". This may be a clue to new
              properties of quantum physics or of gravity "beyond Einstein".
              I present an overview of the puzzles of dark energy and the means
              for unraveling them through cosmological probes. Next generation
              experiments such as the Supernova/Acceleration Probe (SNAP) satellite
              would measure the supernova distance-redshift relation to high accuracy
              and map the evolution of structure and dark matter through gravitational
              lensing. These observations will explore the frontiers of physics and
              aim to uncover what makes up the still unknown 95% of our universe.

Novembre 2004

MERCREDI 24 NOVEMBRE 2004, 14h00, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

            Francesco Sylos Labini (LPT, Orsay)

                 "Non linear structures in gravitation and cosmology"

             I will first give a brief overview of the state of observations of
             large scale structure in the distribution of galaxies in the Universe,
             and also of the main theoretical instrument  --- gravitational N-body
             simulation --- used to explain their origin  in standard cosmological
             models.   I will then discuss the principal properties of the  "non
             linear" structures encountered in both contexts,  describing some of the
             basic  statistical methods for their  characterization.  I explain that
             despite a similar power-law two-point  correlation function
             characterising both cases,  the fluctuations may in fact be
             qualitatively  very different in nature,  and I report observational
             evidence that this is indeed the case.  I conclude with a discussion
             of some of the open theoretical questions raised by these results.

Decembre 2004

MERCREDI 15 DECEMBRE 2004, 14h00, Bibliotheque , LPTHE, Tour 24, 5eme etage, Jussieu

            Hector de Vega (LPTHE, Jussieu)

             "Inflation, cosmic microwave background anisotropies and quantum field theory effects"

            Inflation was proposed to explain the homogeneity, isotropy and flatness of the Universe.
            At the same time, inflation generates the scalar density fluctuations that seed large scale structure,
            thus explaining the temperature anisotropy in the cosmic microwave background (CMB), as well
            as tensor perturbations (primordial gravitational waves). Inflationary models predictions
            (gaussian, nearly scale invariant adiabatic perturbations) are in spectacular agreement both with
            the CMB (the recent WMAP data) as well as with the large scale structure observations. The theory
            of inflation is presented starting from the basic paradigm and its realization as an effective field
            theory for the early universe where inflation turns to act as an attractor. The deep connection
            between inflation and grand unification is stressed. The spectrum of observable primordial fluctuations
            is derived from the inflaton dynamics and the new quantum effects arising from the quantum field
            theory treatment are presented. The inflaton decay during inflation (into lighter particles or into itself)
            induces novel observable effects in the primordial spectrum and generates non-gaussianity.    

Janvier 2005

MERCREDI 26 JANVIER 2005, 14h00,Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Eric Gourgoulhon (LUTH, Meudon)

             "Relativité numérique et sources d'ondes gravitationnelles"

              L'objet de la relativité numérique est de résoudre les équations d'Einstein
              À l'aide d'ordinateurs, pour étudier plus particulièrement les sources astrophysiques d'ondes
              gravitationnelles détectables par VIRGO ou LISA. Ces dernières mettent en effet en jeu
              des objets compacts (étoiles à neutrons, trous noirs) qui ne peuvent ê;tre décrits correctement
              que par la relativité générale. Une particularité de la relativité numérique est qu'elle requiert
              des études analytiques approfondies en préalable à toute implémentation numérique.
              Je présenterai deux de ces études: la première sur la dynamique de l'espace-temps et la
              deuxième sur le traitement local des trous noirs. Enfin je discuterai de l'implémentation
              numérique et présenterai quelques résultats.

Fevrier 2005

MERCREDI 16 FEVRIER 2005, 14h00, Bibliotheque, LPTHE, Tour 24, 5eme etage, Jussieu

            Julien Guy (LPNHE, Jussieu)

             "SuperNova Legacy Survey: Resultats de la premiere annee et implications cosmologiques"

             Les supernovae de type Ia (SNe Ia) forment a l'heure actuelle la classe d'objets la plus
             performante pour etudier l'evolution de la distance de luminosite avec le redshift, et ainsi
             mesurer l'histoire de l'expansion de l'Univers. Des releves anterieurs ont permis de mettre
             en evidence une acceleration recente de cette expansion, due a une hypothetique Energie Noire.
             Il s'agit maintenant de contraindre l'equation d'etat de cette derniere et de mesurer avec
             precision les parametres cosmologiques, ce qui requiert une large statistique. Le SuperNova
             Legacy Survey (SNLS) est a l'heure actuelle le projet le plus ambitieux. Il prevoit d'observer
             plus de 700 SNe Ia, dont les redshifts seront compris entre 0.2 et 1, multipliant ainsi la
             statistique disponible par un facteur 10. Je presenterai les resultats de la premiere annee du SNLS, et
 discuterai leur implication cosmologique.

Mars 2005

MERCREDI 16 MARS 2005, 14h00, Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Felix Mirabel (European Space Observatory & CEA-Saclay-Sap)

             "Black holes in the Universe"

            I will review the observational evidence for the existence of supermassive
            black holes and black holes of stellar-mass. I will concentrate on Microquasars, which
            are stellar-mass black holes in our own Galaxy that mimic,  on a smaller scale, many of
            the phenomena seen in quasars. Microquasars are ideal laboratories to tests the Physics
            in the limits of the strongest gravitational fields. Their discovery has opened the way for
            a new understanding of the connection between accretion of matter onto black holes
            and the origin of relativistic jets seen  everywhere in the Universe. I will review the open
            questions and future perspectives in this new field of research.

Avril 2005

MERCREDI 13 AVRIL 2005, 14h00, Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Riccardo Barbieri (Scuola Normale Superiore, Pisa )

             "Particle Physics and  `fundamental' physics"

            I summarize for non experts the current status of particle physics and I describe
            a possible evolution the field could take in the future.

Mai 2005

MERCREDI 11 MAI, 2005, 14h00, Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Gabriele Veneziamo (College de France et CERN )

             "Conventional vs. Unconventional Cosmic Accelerators"

            We are quite sure that, in its long history, the Universe underwent
            an accelerated expansion at least twice, once in early cosmology,
            and once in our recent past. In either case, we are not sure about what
            provided the repulsive force that is needed to accelerate. I will discuss
            both the most conventional "accelerator candidates" and some less
            conventional ones that appear to be preferred by string theory and
            point out ways to distinguish these alternatives through their
            observational consequences.

Juin 2005

MERCREDI 8 JUIN 2005, 14h00, Bibliotheque, LPTHE, Tour 24, 5eme etage, Jussieu

            Sacha Dolgov (INFN-Ferrara, ITEP-Moscow et LERMA-Observatoire de Paris)

             "Cosmological Magnetic Fields and CMB Polarization"

            The origin of the observed magnetic fields in galaxies and intergalactic
             space presents a profound cosmological mystery. An overview of possible
             mechanisms of their generation is presented . If the large scale magnetic
             fields were created in the early universe they could lead to an observable
             rotation of polarization plane of cosmic microwave background radiation.
             This phenomenon is discussed in detail.

                                                                Année 2003-2004

                                                                                                     Novembre 2003

MERCREDI 26 NOVEMBRE 2003, 14h00,  Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Daniel  Boyanovsky  (LERMA, Observatoire de Paris & University of Pittsburgh)

           "Phase Transitions in the Early and Present Universe"

            I will present a summary of Early Universe cosmology and
            the physics of compact stars stressing the contact with particle
            physics. The succesive phase transitions that happened in the Early
            Universe as well as novel phases in Neutron Stars will be discussed
            including their observational consequence

                                                                                                    Janvier 2004

MERCREDI 14 JANVIER 2004, 14h00,  Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

          Yannick Mellier (IAP)

              " Distortion gravitationnelle et cosmologie"

            Les analyses statistiques de la distribution en ellipticite des
            galaxies montre un champ coherent produit par les effets de lentilles
            gravitationnelle des grandes structures de l'univers (le cosmic shear).
            L'interpretation cosmologique de ce champ permet d'en extraire des
            informations sur les proprietes de la matiere noire, des relations
            matiere-lumiere et de l'energie noire.  Je presenterai l'etat
            actuel de nos connaissance dans le domaine du cosmic shear ainsi que
            les resultats attendus avec le CFHTLS, qui commence tout juste a
            produire les premiere images de megacam, notamment sur l'equation
            d'etat de l'energie noire. Je montrerai ensuite ce que devrait obtenir
            des experiences comme JDEM/SNAP d'ici 10 ans.

Fevrier 2004

MERCREDI 25 FEVRIER 2004, 14h00, Bibliotheque , LPTHE, Tour 16 (1er etage) Jussieu

          Alex Lazarian (Wisconsin-Madison and Cologne)

              "Turbulence and Scaling in Astrophysics"

            I shall introduce the concept of turbulence using Kolmogorov turbulence
            in a non-magnetized incompressible fluid as an example. Then I shall show
            how the properties of the fluid are modified by magnetic fields. Finally  I
            shall talk about the effects of compressibility and partial ionization on the
            properties of magnetic turbulence.
                            Astrophysical fluids are as a rule turbulent, magnetized, compressible
            and sometimes only partially ionized. Star formation, accretion processes,
            cosmic rays transport, polarized radiation and heat, etc are affected by magnetic
                            Recent research also shows that interstellar turbulence is essential
            to understanding the properties of various foregrounds that interfere with the
            measurements of CMB polarization. I shall show that the scattering of cosmic rays
            by the interstellar medium is  substantially changed when the properties of magnetic
            turbulence are taken into account.
                  I shall end my talk by describing how the theory can be tested with observations.

Mars 2004

MERCREDI 17 MARS 2004, 14h00,  Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Joseph Silk (Oxford University)

                "A la recherche de la matiere sombre"

            Je ferai un compte-rendu de l'abondance globale de matiere sombre.
            Je decrirai l'etat actuel de nos connaissances sur la matiere sombre
            baryonique et les possibilites de detection de la matiere sombre

MERCREDI 24 MARS 2004, 14h00,  Bibliotheque , LPTHE, Tour 16 (1er etage) Jussieu

          Robert Brandenberger (Brown University)  

              "Challenges for String Cosmology"

             The inflationary scenario provides the current paradigm
             of early Universe cosmology. Although this scenario has
             been very successful phenomenologically, it is plagued
             by serious conceptual problems. I will discuss some of
             these problems and explain why superstring theory
             might provide a good framework in which to address these
             issues. I will give an overview of some of the key
             challenges which a new paradigm of the early Universe
             based on string theory faces, and will discuss one
             approach to addressing these questions, ``brane gas


Avril 2004

MERCREDI 28 AVRIL 2004, 14h00,  Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Mikhail Shaposhnikov (EPFL Lausanne)

                "Baryon asymmetry of the universe: a window to physics beyond the standard model"

            I will discuss the problem of baryon asymmetry of the Universe and
            different proposals suggested for its solution. All of them require new
            physics beyond the standard model of particle physics.

Mai 2004

MERCREDI 26 MAI 2004, 14h00,  Bibliotheque , LPTHE, Tour 16 (1er etage) Jussieu 

            Patrick Petitjean (IAP)

                "Structures du milieu inter-galactique a grand decalage spectral, formation des galaxies 
                   et variation des constantes fondamentales"

             Le spectre  d'absorption des quasars tres eloignes revele le gaz interpose
             entre nous et le quasar. L'etude de ce milieu  intergalactique et son
             evolution cosmologique montre qu'il constitue le reservoir des baryons
             a partir duquel les galaxies se forment. Un modele coherent de la distribution
             spatiale de la matiere baryonique dans l'Univers a donc emerge dans lequel
             les nuages inter-galactiques se repartissent suivant le reseau filamentaire
             de la matiere noire, dont les noeuds sont les lieux ou se forment de facon
             preferentielle les galaxies. De plus, l'observation du spectre  d'absorption
             des quasars tres eloignes permet de mettre de contraints a la variation avec
             le temps  des constantes fondamentales de la physique: $\alpha_{em}$ et
             $\frac{m_{proton}}{m_{electron}}$ et eventuellement la mesure de
             la temperature du fond diffus.

Juin 2004

MERCREDI 9 JUIN 2004, 14h00,  Salle Grossetete, LPNHE, Tour 33 (RdC) Jussieu

            Neil Turok (University of Cambridge)

                 "A Cyclic Universe Scenario"

              Cosmology has seen dramatic progress in recent years, with observations
              ruling out many popular theories and focussing attention on
              a `concordance model' involving high energy inflation
              in the early universe and low energy cosmic acceleration today.
              The first part of the talk will review some of the key phenomenology which
              singles out this model amongst many rival theories.
              However, the model has deep consistency puzzles: what drives the inflation?
              how did inflation begin? will the future really be a cold, eternal void?
              New ideas from string and M theory on the nature of spacetime
              motivate us to reconsider these questions. We have proposed a new cosmological
              scenario, the `cyclic Universe', in which today's dark energy plays the central role.
              It is required to drive an eternal series of cycles, each consisting of a big bang followed
              by a period of activity followed by accelerating expansion which `cleans up' the
              debris restoring the Universe to a smooth, pristine state ready for the next bang. This
              scenario reproduces the phenomenological successes of inflation with completely different,
              long wavelength physics. It also casts new light on the cosmic singularity, suggesting
              it was not the beginning of time. An observational test distinguishing the cyclic
              model from inflation will be described.