Light Axion-like particles (ALPs) with masses below 1 MeV are strongly constrained by cosmological and beam-dump experiments. The parameter space for heavier ALPs however is largely unconstrained. I will review the current bounds and argue, that collider probes and in particular the exotic Higgs decays h→Za and h→aa can test many orders of magnitude of so far unconstrained parameter space for a variety of ALP decays. Almost the complete region in which ALPs can explain the anomalous magnetic moment of the muon can be probed by searches for these decays with subsequent decay a→γγ even if the relevant couplings are loop suppressed and the a→γγ branching ratio is less than~1.

Les propriétés mécaniques des tissus biologiques sont des paramètres importants en médecine : ce sont des biomarqueurs du fonctionnement normal ou pathologique d’un tissu. En effet, ces propriétés peuvent être affectées par certaines conditions mécaniques (hypertension, traumatisme) mais également par la présence de certaines maladies (cancer, fibrose, maladie d’Alzheimer). La palpation réalisée par le médecin permet de discerner ces changements mais ce geste est qualitatif et ne peut accéder à des organes profonds. L'élastographie par résonance
magnétique (ERM) est une méthode quantitative, robuste et d'une grande précision qui vise à caractériser les propriétés mécaniques des tissus en mesurant les champs de déplacement d'une onde mécanique induite dans un tissu. L'ERM peut être décrite par trois étapes. La première étape consiste à appliquer une contrainte au tissu sous la forme d'une onde mécanique périodique. La deuxième étape est l'enregistrement du champ de
déplacement dans le tissu par IRM en contraste de phase. Enfin, à partir de ces cartes de déplacement, il est possible de revenir aux propriétés mécaniques du tissu par inversion de l'équation d'onde. Après une présentation et un état de l'art de 'élastographie par IRM, deux applications seront présentées. La première concernera la dfficulté
d'appliquer l'ERM aux organes profonds tel que le cerveau et ses
solutions. La seconde application concernera la caractérisation des propriétés mécaniques non linéaire des tumeurs, ici appliquées sur des tumeurs sous-cutanées sur souris, pour peut-être un jour obtenir un indicateur des forces internes tumorales permettant de planifier et suivre le traitement d'un cancer (dans le cadre du projet européen Horizon 2020 No 668039 : Imaging the Force of Cancer).

Even though the LHC searches so far did not unveil the new physics particles, the B-physics experiments at LHCb, BaBar and Belle hint towards deviations from Lepton Flavor Universality in both the tree-level and loop-induced B meson semileptonic decays. I will briefly review the models that can address these puzzles, propose one new model and discuss the main predictions that can be tested at LHCb and/or Belle-II. Particular emphasis will be given to Lepton Flavor Violation in B meson decays, which
offer a very clean alternative to test the proposed New Physics scenarios.

If a liquid is cooled fast enough, it is possible to avoid the phase transition towards a crystalline solid, and the system enters a metastable state, called supercooled liquid. If the cooling continues, the viscosity and the relaxation times grow so steeply that the system becomes effectively solid, even though the system did not undergo any thermodynamic phase transition. Such a solid is called a glass. Glassy materials appear in both in everyday life and in high-tech devices. Further, many systems in biology, computer science and mathematics also exhibit a glassy behavior. In this talk, we try to understand the mechanisms underlying the rigidity of glasses. In phase space, the dynamics of such systems can be regarded as a random walk in a high-dimensional energy landscape. This landscape is rugged, so in order to sample new configurations the system must 'hop' over an energy barrier from one local minimum (basin) to another. This type of process is called activation. We adopt a bottom-up strategy to understand this phenomenon. We start from the simplest models, attempt to fully characterize the behavior of their random walk in phase space, and only then add features representing more realistic glasses. We analyze three paradigmatic mean-field models: the Trap Model, the Random Energy Model (REM) and the p-spin model. In particular, in the REM, we see that despite the motion in configuration space is complex on intermediate time-scales, there is a very large separation of time scales that washes out correlations induced by the exploration of the landscape. As a result, by coarse-graining the dynamical evolution in terms of basins of the energy landscape, the dynamics can be effectively described through a hopping between disconnected traps. This type of description is not applicable anymore in systems with a higher degree of correlation in the energy landscape, such as the p-spin model, where the energy landscape exhibits large basins which are connected one to the other through non-trivial boundaries.

Understanding the mechanisms that lead to glass formation is one of the open problems for the condensed matter research. Numerous questions remain unanswered, because the tremendous increase of relaxation times during the cooling process prevents the exploration of equilibrium properties of supercooled liquids at very low temperature. Computer simulations of glass-forming liquids are nowadays able to reach equilibrium at temperatures comparable to the Mode-Coupling crossover temperature, which is well above the experimental glass transition temperature. As a consequence, simulations lag eight orders of magnitude behind experiments in terms of equilibration times. Progress to close this gap has been slow, and stems mostly from hardware improvements.

In this thesis we make an important step to close this gap. We combine the use of a Monte Carlo algorithm, known as the swap algorithm, with the design of novel glass-forming models. We systematically test numerous models using both discrete mixtures and polydisperse systems. We discuss the role that polydispersity and particle softness play in avoiding crystallization and in efficiently reaching previously unexplored regimes. We study the dynamical processes taking place during swap Monte Carlo simulations. We demonstrate that in some cases our technique is able to produce thermalized configurations at temperatures inaccessible even by experiments.

In this newly accessible regime, we investigate some open questions concerning the glass transition. We show that a hard sphere fluid can be equilibrated at, and even beyond, the jamming packing fraction. We measure the configurational entropy in extremely supercooled liquid, finding a strong dimensional dependence that supports, on the one hand, the existence of an ideal glass transition at a finite temperature in three dimensions and, on the other hand, its absence in two dimensions. We detect the increase of amorphous order quantified through a static point-to-set length throughout the glass formation. We measure the critical exponents introduced in the mean-field theory of glasses much closer to the supposed ideal glass transition. Finally, we reveal the absence of a sharp geometric transition in the potential energy landscape across the Mode-Coupling crossover.

The models and the algorithms developed in this thesis shift the computational studies of glass-forming liquids to an entirely new territory, which should help to close the gap between theory and experiments, and get us closer to solve the long-standing problem of the glass transition.