# Colloquium Paris VIde Cosmologie et Astroparticules

LPNHE, LPTHE & GreCo/IAP
 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)

## 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
satellite"

 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
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 Ã  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
Ã€ 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 Ã  neutrons, trous noirs) qui ne peuvent Ãª;tre décrits correctement
que par la relativité générale. Une particularité de la relativité numérique est qu'elle requiert
des études analytiques approfondies en préalable Ã  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

"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
turbulence.
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
non-baryonique.

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
cosmology".

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.