Effective field theory is one of the deepest and most useful guiding principles in physics. Its tools and methods allow one to study the universal aspects of entire classes of unknown microscopic models, with their main features being captured by symmetries and few relevant parameters of the effective degrees of freedom. Because of its universality, it finds  applications across all scale in physics: from super-Hubble scales all the way to the Planck length. It is successfully applied to cosmology to describe the early cosmic inflation, the current cosmic acceleration, the dynamics of the large scale structure and the dark matter. Its methods have found recent applications in the theory of gravitational wave emission by binary inspirals, and in the new multimessanger astrophysics: new and conceptually compelling ways to perform calculations and predictions are being developed by making contact with the methods of scattering amplitudes of particle physicists. ...

This past year a team at IPhT around John Joseph Carrasco — in collaboration with physicists at UCLA and Penn State University in the United States, and Uppsala University in Sweden — completed a calculation long thought to be impossible: the direct understanding of the dimensions of space-time in which the most symmetric particle-based field theory of gravity (maximal supergravity) would cease to be predictive when quantum effects are relevant. One can isolate order by order the quantum effects in graviton scattering. For two gravitons scattering off of each other, this calculation required consideration of the fifth-order quantum correction. This puts strong constraints on the behavior of fundamental symmetries in controlling the high-energy behavior of this theory.
 
To give an idea of the size of the problem, consider a word count of everything ever written by human beings (from cuneiform tablets and stone carvings to books, magazines, emails, etc). This was estimated at one time to be some 40 quadrillion words. ...

Periodically driven quantum many-body systems (such as cold atoms in time-dependent optical lattices and quantum materials under ultra-fast optical excitation) offer exciting perspectives of exploring quantum phases of matter along genuine non-equilibrium pathways.This so-called Floquet engineering relies, however, on the suppression of heating, i.e. the uncontrolled energy absorption from the drive. This was known to be the case only in the limit of extremely high frequency,thus limiting its practical use.

A team at IPhT around Francesco Peronaci, Marco Schiro and Olivier Parcollet showed that also strong electronic interactions can largely circumvent energy absorption, and thus provide a robust
platform for Floquet engineering even at finite frequency. This is demonstrated with non-equilibrium dynamical mean-field calculations
on a driven Fermi-Hubbard model, a paradigmatic example of lattice correlated electrons. ...