Théorie

As is well known, the string spectrum comprises infinitely many states that can collectively be visualized along Regge trajectories of increasing mass and spin. Its massless and lightest levels, as well as certain higher spins including the leading Regge trajectory, have been the focus of past studies. In principle, access to any state is possible, but the traditional methodology is non-covariant and does not immediately lead to irreducible representations of the Wigner little group. In this talk, we will discuss a new and covariant technology of constructing the string spectrum.

Developing non-perturbative methods might be crucial for understanding inflation and its predictions. In this talk, I will present a nonlinear study of the inflationary epoch of the Universe based on numerical lattice simulations. I will first focus on a model known as axion inflation, where the inflaton is coupled to a gauge field via Chern-Simons interaction. As a second example, I will consider a single-field model with a resonant feature in the potential. I will show that, in both cases, nonlinear effects have important consequences for the inflationary dynamics.

We will construct and analyse explicit solutions in scalar tensor theories parametrised by two independent charges : their ADM mass and an additional primary hair associated to the minimally coupled scalar field. A special relation between the two will render the solutions regular everywhere and at the origin in particular.

Both Einstein's equations and the field equations of a modified theory of gravity can be derived as equations of state from purely thermodynamical considerations, leading to the identification of GR with an equilibrium state of gravity and modified gravity with a non-equilibrium one. This breakthrough made the relationship between gravity and thermodynamics even more intriguing. I will present a new approach to the thermodynamics of modified gravity which is inspired by these results, but follows a starkly different path.

The observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory has opened up a new window to the universe. These neutrinos traverse the longest distances from their sources and have the largest energy ever observed. These neutrinos open a new trail to search for new physics that covers parameter space not accessible to terrestrial neutrino experiments.

Boyer Théo
Cosmological magnetic fields 

Ivanez-Ballesteros Pilar

Supernova neutrinos and nonradiative neutrino decay

Hořava-Lifshitz gravity has been proposed as a ghost-free and renormalizable quantum gravity model candidate with an anisotropic UV-scaling between space and time. In my talk I would like to present a cosmological background analysis of two different formulations of the theory, with particular focus on the running of the parameter λ with energy.

The problem of identification of ultra-high-energy cosmic ray (UHECR) sources is greatly complicated by the fact that even the highest energy cosmic rays may be deflected by tens of degrees in the galactic magnetic fields. We show that arrival directions of UHECRs from several nearest active galaxies form specific patterns in the sky, which can be effectively recognized by convolutional neural networks.

The expansion of the universe spontaneously breaks time translation by selecting a preferred reference frame. As a consequence, very much like a superfluid at zero temperature, the low-energy description of single field inflation can be organised in terms of the associated Goldstone mode of the broken symmetry (aka the phonon).