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Théorie

Strong infrared effects in de Sitter spacetime: between gauge-artifacts and secularity

Orateur: 
Ahmed Youssef
Home Institute: 
Humboldt Universität zu Berlin
Lieu: 
483A Malevitch
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.

Hubble diagram and fluid limit in cosmology

Orateur: 
Pierre Fleury
Home Institute: 
IAP
Lieu: 
483A Malevitch
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.

Quantum properties of a non-Gaussian state

Orateur: 
Florian Gautier
Home Institute: 
APC
Lieu: 
483A Malevitch
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.

Integral quantization or exploring the world in the manner of a starfish

Orateur: 
Jean Pierre Gazeau
Home Institute: 
APC
Lieu: 
483A Malevitch
Horaire: 
Tuesday, 2. April 2013 - 14:00

 

Climbing scalars and implications for cosmology

Orateur: 
Emilian Dudas
Home Institute: 
Ecole Polytechnique
Lieu: 
483A Malevitch
Horaire: 
Tuesday, 26. March 2013 - 14:00

 

Can Planck disprove anisotropic inflation?

Orateur: 
Jiro Soda
Home Institute: 
Kyoto University
Lieu: 
483A Malevitch
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.

Naturally inflating on steep potentials through electromagnetic dissipation

Orateur: 
Lorenzo Sorbo
Home Institute: 
University of Massachusetts
Lieu: 
483A Malevitch
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?

Orateur: 
Fabien Nugier
Home Institute: 
LPTENS
Lieu: 
483A Malevitch
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.

Modifications of gravity: what can we measure in principle?

Orateur: 
Ignacy Sawicki
Home Institute: 
University of Heidelberg
Lieu: 
483A Malevitch
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.

Post-Newtonian approach to spin-orbit effects in inspiralling compact binaries

Orateur: 
Sylvain Marsat
Home Institute: 
IAP
Lieu: 
483A Malevitch
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.

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