# Théorie

# 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.

# Could quantum theory explain the origin of the inflationary period?

# Isotropy-breaking in Quantum Cosmology

We present a new perspective in QFT on quantum cosmological space-times. Naively, the semiclassical limit of a quantum space-time can be taken by averaging the gravitational operators on a semiclassical state of the geometry. The result is an effective classical metric (which in general does not obey the Einstein equations).

# How to shape a black hole with matter fields

The main interest of the work exposed in this seminar is to explore new black hole solutions in a more general framework than General Relativity. A first extension will be detailed with the introduction of higher dimensions and p-form fields. These fields constitute the natural generalization of the electromagnetic interaction. We will build in this context new static black hole solutions where p-form fields allow to shape the geometry of the horizon.