# Théorie

# Modifications of gravity: what can we measure in principle?

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

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.

# Do gluons have a mass?

# Galilean Genesis

I will describe possible alternatives to inflation, based on the spontaneous breaking of conformal invariance. I will study the possibility of violating the Null Energy Condition in these models and work out their predictions, which are severely constrained by the non-linear realization of the conformal group.

# The Higgs boson mass and Standard Model up to the Planck scale

The Higgs boson with the mass announced by the LHC experiments corresponds within current precision to the boundary value between the situations when the electroweak vacuum is stable and metastable. I will discuss the developments in the calculation of this boundary mass and importance of measurement of other SM parameters (top quark mass and the strong coupling constant) at the lepton collider.

# Second-order Boltzmann code and the CMB bispectrum from recombination

I will introduce CosmoLib2nd, a numerical Boltzmann code at second-order to compute CMB bispectra on the full sky. We compute the cosmic microwave background temperature bispectrum generated by nonlinearities at recombination on all scales. For cosmic-variance limited data to l_max = 2000, its signal-to-noise is S/N=0.47 and will bias a local signal by f_NL^{loc} ~ 0.82.

# Light sterile neutrinos as dark radiation candidates

# Dark energy: an effective field theory approach.

The discovery of the accelerating expansion of the Universe is triggering an impressive amount of theoretical and observational activity. After briefly reviewing the problems and challenges of "Dark Energy", I will focus on recent and ongoing works in which my collaborators and I propose a unifying description of dark energy and modified gravity models that makes use of effective field theory (EFT) techniques. EFT allows to isolate the relevant low energy degrees of freedom and to efficiently study their dynamics.

# Generalized Multi-Scalar-Tensor theory in arbitrary dimensions

After a brief introduction on modified gravity, scalar-tensor theories and the Ostrogradski theorem, I will talk about the most-general multi-scalar-tensor theory that is free of Ostrogradski ghosts, i.e., with equations of motion with derivative order up to two [arxiv.org/abs/1210.4026]. I will also touch upon the possible applications of this powerful general framework.