Despite its chemical simplicity, boron trioxyde appears a puzzling system, as it does not crystalles under normal conditions of temperature and pressure. It was hypothesized, based on DFT calculation in the GGA approximation, that this 'crystallization anomaly' resulted from the existence of a 'hidden' low energy polymorphism (see Ref. 1).
In a previous work, we showed that including dispersion effects was critical for an accurate description of the volume and energetics of SiO2 polymorphs (see Ref. 2). SiO2 and B2O3 being the two textbook examples of network forming oxydes, it is to be expected that dispersion effects also play a crucial role in the ab initio description of B2O3's hidden polymorphism. We consequently use van der Waals corrected density functional theory and Quantum Monte Carlo to investigate B2O3 polymorphs. We show that some conclusions of Ref. 1 must be modified, and we use this methodology to predict the properties of the newly found polymorphs. It is demonstrated that most structures have interesting mechanical properties, including high porosity, strong anisotropy, and negative linear compressibility.

Ref. 1 : 'Hidden polymorphs drive vitrification in B2O3', Guillaume Ferlat, Ari Paavo Seitsonen, Michele Lazzeri & Francesco Mauri,Nature Materials 11, 925-929 (2012).

Ref. 2: 'Dispersion effects in SiO2 polymorphs: An ab initio study', Henri Hay, Guillaume Ferlat, Michele Casula, Ari Paavo Seitsonen, and Francesco Mauri, Phys. Rev. B 92, 144111 (2015)

The study of out-of-equilibrium thermodynamics has received a significant thrust thanks to the experimental advances in the control and manipulation of microscopic systems. Work, an ubiquitous concept in traditional thermodynamics, assumes in this context the role of a stochastic variable whose fluctuations can be ingeniously related to equilibrium properties, as is the case of the celebrated Jarzynski equality. In this talk, I will revise these concepts and discuss a feasible experimental scheme to directly measure work in cold atomic setups. I will show that the interaction between atoms and the light polarisation of a probe laser, as in atomic ensembles experiments, allows us to implement such POVM. In this way the work done on or extracted from the atoms after a given process is encoded in the light quadrature that can be measured with a standard homodyne detection. The protocol allows one to verify fluctuation theorems and study properties of the non-unitary dynamics of a given thermodynamic process [1]. A second scheme allows one to measure the work done on an atomic BEC in a double well potential when the atomic self-interaction is varied. I will discuss strategies based on optimal control techniques to reduce the irreversible work production.

References
G. De Chiara, A. J. Roncaglia, J. P. Paz, New J. Phys. 17, 035004 (2015)

Cosmological Inflation is one of the leading paradigms for explaining the
physical conditions that prevailed in the early Universe. It consists in a
phase of very high energy accelerated expansion that solves the hot
big bang model problems. When combined with Quantum Mechanics,
it also provides a causal mechanism for generating cosmological fluctuations
on large scales.

In this talk I will explain how the most up-to-date cosmological observations,
incorporated in the Bayesian model comparison approach, can be used to
extract the favoured models among hundreds of proposed scenarios.
I will insist on the role played by reheating, which connects inflation to
the subsequent radiation era, and during which ordinary matter as we see it
today is produced. I will also discuss some extensions to the
minimal single-field setups, where extra scalar fields are added and play
a role both during inflation and reheating.

Approaching a critical point, the divergence of the correlation length of fluctuations can be cut-off by a confinement of the system. This truncation fosters finite size effects with universal features, such as the critical Casimir force which has particularly drawn attention in the past decades. I will describe how the critical Casimir force arises in confined critical systems and how its universality has led to a clear separation between numerical/theoretical approaches and experimental approaches. On the one hand, theoretical and numerical works on the subject have almost systematically been performed in magnetic model systems, such as the Ising or XY models. On the other hand, experimental approaches were all realized in fluid systems, such as binary mixtures or helium IV close to the superfluid transition. I will then present two very different numerical approaches, both intended to bridge this gap. Firstly, I will present a numerical test of an experimental protocol for measuring the critical Casimir force in a magnetic layer and, secondly, a numerical approach in a Lennard-Jones binary mixture. These approaches could open the way to a variety of experimental approaches in magnetic thin films and to studying fluctuations or out-of-equilibrium aspects of the Casimir force in simulations of fluids.

I will present a one-parameter generalization of the symmetric simple exclusion process on a one dimensional lattice. In addition to the usual dynamics (where particles can hop with equal rate to the left or to the right with an exclusion constraint), annihilation and creation of pairs can occur. The system is driven out of equilibrium by two reservoirs at the boundaries. In this setting the model is still integrable: it is related to the open XXZ spin chain through a gauge transformation. This allows us to compute the full spectrum of the Markov matrix using Bethe equations. Then, we deduce the spectral gap in the thermodynamical limit. We also show that the stationary state can be expressed in a matrix product form permitting to compute the multi-points correlation functions as well as the mean value of the lattice current and of the creation-annihilation current. Finally the variance of the lattice current is exactly computed for a finite size system. In the thermodynamical limit, it matches perfectly the value obtained from the associated macroscopic fluctuation theory. It provides a confirmation of the macroscopic fluctuation theory for dissipative system from a microscopic point of view.

Studying the underlying theory of composite Higgs models can reveal many features of their phenomenology.
In the context of fermionic gauge theories, which are naturally free of the hierarchy problem, I will discuss
how the Higgs may be accompanied by a Dark Matter candidate, and how di-boson signatures can be a
smoking gun at the LHC. The ATLAS/CMS di-photon resonance, if confirmed, would be a strong discriminator,
leading to neat predictions with the aid of Lattice calculations.

Acoustic or blast wave absorption by liquid foams is especially efficient and bubble size or liquid fraction optimization is an important challenge in this context. A resonant behaviour of foams has recently been observed in linear acoustics, but the main local dissipative process is still unknown. We address this issue by measuring the pressure attenuation of a weak shock wave in a liquid foam, in the linear and weakly non-linear regimes. I will show that the pressure attenuation depends on the nature of the gas composing the foam and that a maximum of attenuation is obtained for a given bubble size. Those results are interpreted with a thermal dissipation model, featuring an optimal attenuating bubble size close to the thermal boundary layer. If I have time, I will also present some results on the foam rupture after the impact of the blast wave.