Plenary Session 1
Contact: Roland Triay (CPT) – triay[at]cpt.univ-mrs.fr
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The search for the nature of the dark sector relies on the combination of multiple techniques and probes, from both spectroscopic and photometric data. This matches well with the fact that some probes are intrinsically 3D (like RSD) and some 2D (like WL). But to get the best constraints we need to combine all of these. We show how using angular cross-correlations we can recover the full 3D galaxy clustering information, including BAO and RSD in spectroscopic surveys. This allows the combination of spectroscopic and photometric galaxy surveys, including photo-z error calibration and addition of WL. We show some application of these ideas in current data and simulations and show how overlapping surveys result in both better constrains and better understanding of systematic errors.
A critical assessment of the observed large scale structure will be presented, starting from the Local Group of galaxies within 5 Mpc, out to . Traditional and new probes will be shown to support the standard paradigm of structure formation, but not without raising a few eyebrows. Mild tweaks will be discusses as well as potential constraints on alternative theories of gravity.
Measuring distances to supernovae (or more precisely to the “type Ia” subclass) has allowed us to measure the distance-redshift relation beyond linear order for the first time in 1998. These first results already showed strong evidence for an accelerated cosmological expansion at the present epoch. This has been confirmed by several other cosmological probes, but what causes this accelerated expansion remains elusive. Our ignorance is commonly parametrized using the “equation of state of dark energy”, where dark energy refers to the fluid one can postulate to source the acceleration. I will present how supernova measurements have evolved since the discovery, review the latest dark energy constraints, and discuss the future of the probe.
Weak gravitational lensing by inhomogeneities along the line-of-sight alters the shapes, sizes and fluxes of distant sources such as galaxies, and distorts the pattern of continuous fields such as the microwave background radiation. In this talk I will review this relatively young scientific field, with particular emphasis on its power for studying dark energy and modified gravity. I will discuss the challenges it faces, summarize results from recent survey analyses, and finally consider the prospects for the future
As microwave background photons propagate from the surface of last scatter to our telescopes, they are affected by four distinct processes in the low redshift universe: gravitational lensing, the thermal Sunyaev-Zeldovich (tSZ) effect, the kinematic Sunyaev Zeldovich (kSZ) effect and the intervening Sachs Wolfe effect (ISW). This talk will focus on the kSZ and ISW effect. I will discuss the cross-correlations between the large-scale distribution of galaxies and these two effects and show how current and future measurements can be used to probe the growth rate of structure and gravitational physics on large-scales.
After more than fifteen years, the discovery that the Universe is accelerating emerges as one of the turning points in the history of cosmology, as witnessed by the 2011 Nobel Prize in Physics to Perlmutter, Riess and Schmidt. Yet, the origin of the accelerated expansion is a mystery. One possibility is that the Universe is permeated by a “dark energy” producing a kind of gravitational repulsion. Alternatively, perhaps the very equations of General Relativity need to be modified or generalized to higher-dimensional worlds.
Galaxy redshift surveys are one of the experimental pillars that contributed significantly to build this overall scenario and even larger projects are ongoing or planned, with the goal of understanding the nature of cosmic acceleration. In my talk I will review this situation and show how redshift surveys allow us to possibly break the degeneracy between dark energy and modified gravity by measuring both the expansion rate and the growth rate of structures. I will present recent examples, including results from the new VIPERS survey at the ESO Very Large Telescope. I will then discuss status and plans for the ultimate dark-energy experiment , the ESA satellite Euclid, which is due to launch in 2020. Euclid promises to reach percent accuracies on the measurement of cosmological parameters, with unprecedented control of systematic effects.
Cosmic inflation in the very early universe provides a framework in which to understand the seeds of large-scale structure in our Universe. A rapid, accelerated expansion at ultra-high energies can stretch quantum vacuum fluctuations up to extra-galactic scales. I will discuss the impact of recent observations of the cosmic microwave background sky which provide evidence of primordial density perturbations and now, for the first time, possible evidence for primordial gravitational waves as predicted by inflation. I will discuss how inflation compares with alternative models for the origin of structure and how we might further test the physics of inflation through cosmological observations.
 M. Anselmino, A. Efremov and E. Leader,The theory and phenomenology of polarized deep inelastic scattering, ys. Rept. 261 (1995) 1 [Erratum ibid 281 (1997) 399] [hep-ph/9501369].
 R. Penrose and W. Rindler, Spinors and Space-time, Vol. 2: Spinor and twistormethods in space-time geometry, Cambridge University Press, Cambridge U.K.(1986), pg. 501.
I will review both the general problem of the search for non-Gaussian signatures in cosmological perturbations, originated from inflation in the early Universe. I will discuss this issue both from the theoretical point of view and in connection with constraints coming from recent observations and future prospects for observing/constraining them.
The inflationary scenario is currently considered to be the most promising paradigm to describe the origin of the perturbations in the early universe. It corresponds to a period of accelerated expansion before the hot Big Bang phase. Inflation is typically achieved using scalar fields, and it is the quantum fluctuations associated with the scalar fields that are responsible for the creation of the primordial perturbations. The perturbations generated during inflation leave their signatures as anisotropies in the Cosmic Microwave Background (CMB). With the CMB anisotropies being measured to greater and greater precision, we are presently in an unprecedented situation of being able to arrive at strong constraints on the physics of the early universe. In this talk, after a brief introduction to inflation, I describe the implications of the recently released Planck & BICEP2 data for inflation and discuss what are the “best” inflationary scenarios.
 J. Martin, C. Ringeval and V. Vennin, Encylopedia Inflationaris, to appear in Journal of the dark universe [arXiv:1303.3787].
 J. Martin, C. Ringeval, R. Trotta and V. Vennin, The Best Inflationary Models after Planck, JCAP1403, 039, 2014, [arXiv:1312.3529].
 J. Martin, C. Ringeval and V. Vennin, K-inflationary Power Spectra at Second Order, JCAP1306, 021, 2013, [arXiv:1303.2120].
I will review some of the recently uncovered connections between dark energy and modified gravity. Dark energy involves light scalar fields which would naturally lead to deviations from Newton's law in the solar system. Those are extremely constrained by gravity tests. I will present how one can reconcile dark energy on large cosmological scales with gravity as tested in the solar systems. For that, I will introduce screened modified gravity models and discuss their properties.
Motivated in part by the wish to “replace” dark energy by a large distance modification of gravity, a large body of works has lead to a better understanding of properties and pathologies of theories of “massive gravity”, and closely related models such as “Galileons”. This body mainly developped from the Dvali-Gabadadze-Porrati (DGP) model which was proposed almost 15 years ago - and was the first framework which linked explicitly the cosmic acceleration with a large distance modification of gravity - and culminated with the more recent de Rham-Gabadadze-Tolley (dRGT) theory which is now believed to avoid certain pathologies present in previous constructions. Inbetween, these works also lead to several other proposals, many of which using the “Vainshtein mechanism” to hide at intermediate distances effects which only show up at cosmological scales. I will review these works stressing in particular the left over open questions.
The discovery of the accelerated expansion of the Universe has come relatively late in our study of the cosmos, but in showing that gravity can act repulsively, it has opened up many new questions about the nature of gravity and what the Universe might contain. Is the acceleration being driven by dark energy? Or is general relativity (GR) itself in error, requiring a modification at large scales to account for the late acceleration? Structure formation in our Universe can be different even if the geometry of the homogeneous and isotropic universe is the same in these two classes of models, offering a possibility to distinguish between them observationally. Non-linear structure formation is complicated by the fifth force that commonly appears in modified gravity models and new techniques are required to analyse it. We will discuss novel methods to test GR on cosmological scales, building on the recent developments of N-body simulations for modified gravity.