Our universe is homogeneous an isotropic on very large scales. However, when we go down to smaller scales inhomogeneities become more and more important. Given that Einstein equations are non-linear, it is clear than averaging and time-evolution are operations that do not commute. Thus, it is a crucial question to be addressed the importance of the non-commutativity of these two operations when we measure observables of the background cosmology. In General Relativity and a universe dominated by dust, there seems to be a general consensus that these corrections are small. However, when we consider modified cosmologies (either multifluid scenarios or alternative theories of gravity), the issue remains unclear. Moreover, this will need to be addressed to be able to use the next generation of high precision cosmological data to constrain such alternative scenarios.
External collaborators: Peter Dunsby (University of Cape Town), Alvaro de la Cruz Dombriz (Universidad Complutense de Madrid), Diego Saez (University of the Basque Country.
The first measurements of acoustic peaks in the CMB anisotropies strongly suggest that the birth of cosmological fluctuations may have taken place during an early inflationary era of the universe.
In this domain, our activities deal with the construction of explicit models of inflation as well as the extraction of their observable consequences. Our fields of expertise comprise some actively debated subjects as the existence of features (e.g. trans-Planckian effects), inflation with non-minimally coupled scalar fields, DBI- and brane inflation as in the context of String Theory.
For all these theories, we are maintaining various numerical tools such as the ASPIC and FieldInf librairies allowing to compute reheating-consistent predictions for comparison with cosmological data.
External collaborators: Jérôme Martin (IAP, Paris, France), Vincent Vennin (Portsmouth, U.K.), Sébastien Clesse (RWTH, Aachen, Germany).
Born-Infeld inspired theories. Although General Relativity has proven to be very successful in the scales where it has been tested, when going to high curvature regimes it is commons the appearance of singularities like the Big Bang and/or black holes singularities. This motivates the modification of gravity in such a regime to try to regularize those singularities. We study a natural extension of these models and study their predictions in cosmology and astrophysics
External collaborators: Jose Beltran Jimenez (CPT, Université de Marseille), Lavinia Heisenberg (University of Stockholm), Gonzalo Olmo (University of Valencia).