Home Institute:Humboldt Universität zu Berlin
Horaire:Tuesday, 23. April 2013 - 14:00
Understanding massless scalar fields and gravitons in de Sitter spacetime is of paramount importance for cosmology. This remains however a difficult problem due to strong IR effects. In this talk we identify and study two particular de Sitter IR aspects, namely gauge-artifacts and secular perturbation theory. First, we show that the long-distance behavior of the photon field two-point function is highly gauge-dependent.
Horaire:Tuesday, 16. April 2013 - 14:00
In standard cosmology, the interpretation of the Hubble diagram - constructed from the observation of standard candles such as supernovae (SNe) - relies on the assumption that light propagates in a Friedmann-Lemaître spacetime. However, this assumption does not seem realistic for the very narrow light beams involved in SNe observations, which rather probe the lumpy small-scale structure of the universe. Thus, one can wonder about the influence of such inhomogeneities on the propagation of light, and their impact on the observed Hubble diagram.
Horaire:Tuesday, 9. April 2013 - 14:00
I will present the properties of a non-Gaussian density matrix for an O(N) scalar field in the context of the incomplete description picture. This is of relevance for studies of decoherence and entropy production in quantum field theory which play a key role in timely physics.
Orateur:Jean Pierre Gazeau
Horaire:Tuesday, 2. April 2013 - 14:00
Home Institute:Ecole Polytechnique
Horaire:Tuesday, 26. March 2013 - 14:00
Home Institute:Kyoto University
Horaire:Tuesday, 19. March 2013 - 14:00
In the conventional inflationary scenario, the statistical property of primordial fluctuations can be characterized by a statistically isotropic, Gaussian, and scale invariant power spectrum. However, in the presence of a vector field and its coupling to an inflaton, there could be vector hair during inflation which causes anisotropy in the expansion and the statistical property of primordial fluctuations. We named the model anisotropic inflation.
Home Institute:University of Massachusetts
Horaire:Tuesday, 12. March 2013 - 14:00
Do structures affect the average and variance of the distance-redshift relation in the concordance model of cosmology?
Horaire:Tuesday, 5. March 2013 - 14:00
I will try to give you an answer to that physically relevant question - and its implications on SNe Ia experiments - by taking advantage of the recent formulation of covariant averaging on the past light cone.
Home Institute:University of Heidelberg
Horaire:Tuesday, 26. February 2013 - 14:00
The difference between various models of dark energy or modifications of gravity becomes apparent at the level of growth of large-scale structure in the universe. In addition to measuring the background expansion, we are now beginning to probe this aspect.
Horaire:Tuesday, 19. February 2013 - 14:00
The upcoming new generation of ground-based detectors such as LIGO and VIRGO is likely to allow for the first direct detections of gravitational waves, opening a new window on the universe and on extreme events in the regime of strong-field gravity.