Non-Gaussianities from isocurvature modes

This contribution discusses isocurvature modes, in particular the non-Gaussianities of local type generated by these modes. Since the isocurvature transfer functions differ from the adiabatic one, the coexistence of a primordial isocurvature mode with the usual adiabatic mode leads to a rich structure of the angular bispectrum, which can be decomposed into six elementary bispectra. Future analysis of the CMB data will enable to measure their relative weights, or at least constrain them. Non-Gaussianity thus provides a new window on isocurvature modes. This is particularly relevant for some scenarios, such as those presented here, which generate isocurvature modes whose contribution in the power spectrum is suppressed, as required by present data, but whose contribution in the non-Gaussianities could be dominant and measurable.Comment: 8 pages, 2 figures; to appear in the Proceedings of COSGRAV-2012 (International Conference on Modern Perspectives of Cosmology and Gravitation), Indian Statistical Institute, Kolkata, India, February 7-11, 201

Cosmological evolution in a brane-universe

The idea of extra-dimensions has recently gone through a renewal with the hypothesis, suggested by recent developments in string theory, that ordinary matter is confined to a sub-space, called brane, embedded in a higher dimensional spacetime. I summarize here some consequences in cosmology of this type of models. The most remarkable aspect is that the Friedmann laws, which govern the expansion of the Universe, are modified. An important direction of research is the study of cosmological perturbations and the possible signature of extra-dimensions in cosmological observations.Comment: 2 pages, "mprocl.sty" with LaTeX 2.09; contribution to the 9th Marcel Grossmann Meeting (MG9), Rome, July 200

Cosmological perturbations from multi-field inflation

We briefly review the standard derivation of the spectra of cosmological perturbations in the simplest models of inflation. We then consider models with several scalar fields, described by Lagrangians with an arbitrary dependence on the kinetic terms. We illustrate our general formalism with the case of multi-field DBI inflation.Comment: Invited plenary talk at ICGC-07 (International Conference on Gravitation and Cosmology), 17-21 December 2007, IUCAA, Pune, India; 10 pages, no figur

Gravitation and cosmology in brane-worlds

In brane-worlds, our universe is assumed to be a submanifold, or brane, embedded in a higher-dimensional bulk spacetime. Focusing on scenarios with a curved five-dimensional bulk spacetime, I discuss their gravitational and cosmological properties.Comment: 20 pages; invited plenary talk at the GR17 conference, Dublin, Ireland, July 200

Glimpses into the early Universe

This contribution gives a brief overview of the theoretical ideas underlying our current understanding of the early Universe. Confronting the predictions of the early Universe models with cosmological observations, in particular of the cosmic microwave background fluctuations, will improve our knowledge about the physics of the primordial Universe.Comment: Invited talk at the XVI International Congress on Mathematical Physics, Prague, 3-8 August 2009; 6 page

Primordial non-Gaussianities

This contribution gives an overview on primordial non-Gaussianities from a theoretical perspective. After presenting a general formalism to describe nonlinear cosmological perturbations, several classes of models, illustrated with examples, are discussed: multi-field inflation with non-standard Lagrangians, modulaton fields, curvaton fields. In the latter case, a special emphasis is put on the isocurvature perturbations, which could leave a specific signature in non-Gaussianities.Comment: Invited talk at YKIS (Yukawa International Seminar) 2010: "Cosmology -The Next Generation-", 28 June - 2 July 2010, Kyoto, Japa