Orateur:Mikael Von Strauss
Home Institute:Stockholm University
Horaire:Tuesday, 11. June 2013 - 14:00
Finding consistent generalisations of General Relativity has been very challenging, but its pursuit has (at least) two strong motivations. One is to find out if it is possible to confront cosmological observations without introducing Dark sectors. The other is that it is very rare in field theory to come across new consistent theories and history has taught us that, once they are found, they often have a place in our understanding of nature.
Lieu:454A Luc Valentin
Horaire:Monday, 3. June 2013 - 14:00
We focus on zero-temperature phases of strongly-coupled holographic superfluids at finite density. We show that they can be classified according to their scaling symmetries, as well as the behavior of the electric flux in the deep IR. In the presence of a running scalar, these phases may display hyperscaling violation, which measures the breaking of rigid scaling symmetry in the IR.
Horaire:Tuesday, 28. May 2013 - 14:00
Home Institute:National Centre for Nuclear Research Warsaw, Poland
Lieu:454A Luc Valentin
Horaire:Thursday, 16. May 2013 - 14:00
Horaire:Tuesday, 14. May 2013 - 14:00
During the NASA press conference following the first release of the WMAP data, John Bahcall summed up by saying
that "the biggest surprise is that there is no surprise." I will discuss to what extent this statement holds for the first
Planck release, where some but not all of the predictions for what Planck would see have been borne out.
Horaire:Tuesday, 7. May 2013 - 14:00
Scalar-tensor theories of gravity are natural phenomenological alternatives to General Relativity, where the gravitational interaction is mediated by a scalar degree of freedom, besides the usual tensor gravitons.
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