The viscosity of a suspension is known to diverge when the suspension becomes too dense, that is when the particle volume fraction approaches the jamming fraction. Most models used too describe this divergence are partly or fully empirical, and treat the jamming fraction as an adjustable parameter. We introduce a novel physical interpretation of the jamming fraction as the range of motion of particles. This range of motion can be computed by considering an equivalent granular packing. First, this approach provides us with a scaling law for the viscosity, which fits well the experimental measurements at low shear rate. Second, it helps understand why confined suspensions exhibit a higher viscosity. Finally, it enables to compute the viscosity of polydisperse suspensions by considering the jamming fraction of polydisperse granular packings.

In a second part, we investigate the detachment of suspension drops, first monodisperse, then bidisperse. Through scaling arguments, we show that the pinch-off accelerates through a dislocation mechanism, in which the particles move away from each other. The threshold to this regime is set by the suspension viscosity. Using our model for the viscosity, we are able to caracterise the detachment for a suspension of monodisperse or bidisperse particles.

In the first part of the talk I will talk about a new joint solution of the electroweak hierarchy problem and strong-CP problem [2106.04591]. This mechanism extends the SM with just two axion-like scalars and predicts correlated signals in future hadronic EDM experiments and searches for dark matter. In the second half I will start from the mechanisms discussed in the first half to identify the general features that appear in models that explain the observed value of the weak scale cosmologically. This will lead me to introduce the concept of 'weak scale trigger' [2012.04652] and its phenomenology.

Natural biomaterials originating during the growth cycles of all living organisms have been used for many applications. They span from bioinert to bioactive materials including bioinspired ones. As they exhibit an increasing degree of sophistication, natural biomaterials have proven suitable to address the needs for multiple applications. The objective of the presentation is to discuss our research studying cellulose from biodiverse sources in Ecuador and their biomedical, environmental, and food applications based on specific projects developed in Yachay Tech in collaboration with colleagues from around the world.

Abstract: We begin with a brief introduction to some of the main concepts in the Swampland program, focusing on infinite distance limits in moduli space and their relation to towers of light particles and global symmetries. After that, the existence of membranes becoming tensionless in such infinite distance limits, as well as their role to prevent the appearance of generalised global symmetries will be discussed. Finally, a Gravitino Distance Conjecture will be introduced and motivated from the relation with the aforementioned tensionless membranes, as well as from string theory examples, and some phenomenological implications will be presented.

L'apprentissage automatique piloté par les données est apparu pour pallier les limites des méthodes traditionnelles de modélisation des interactions interatomiques dans les matériaux, telles que la théorie fonctionnelle de la densité électronique et les potentiels semi-empiriques. L'approche implique un modèle mathématique et des données de mécanique quantique. Nous nous concentrons sur les méthodes d'apprentissage automatique pour développer un potentiel tenseur de moment, en particulier sur la génération de bases de données, ainsi que sur une mise en œuvre préliminaire d'un modèle d'apprentissage automatique pour le silicium, qui sera ensuite étendu aux minéraux argileux.

Aging represent a limiting factor in the performances of soft-solid-based products and devices. Many efforts have been devoted to understand the microscopic origin of this long-term behavior in physical gels. In this contribution, we investigate macromolecular physical gels (strontium alginates) at different aging times, combining linear stress relaxation and dynamic light scattering. Stress relaxation shows two-step decay, with an early logarithmic decay followed by a stretched exponential behavior. Two characteristic times can be identified, which increase as distinct power laws of the gel age. The DLS clearly displays anomalous microscopic dynamics, with compressed exponential decay of autocorrelation functions and ballistic wavelength dependence of the decay time. The comparison between rheology and DLS allows for the identification of two dynamic correlation lengths: λ_o and λ_s(fig. 1a). The former (λ_o) is roughly constant with the aging time, while the latter (λ_s) increases linearly with t_w. Overall, rheological and DLS data allow us to attribute the observed mechanical decay to two different mechanisms occurring in our macromolecular physical gel. The first, visible at early-to-medium times, is ascribed to local rearrangements in the gel network (on length scale smaller than the pore size). The second, which occurs at long times, results from collective rearrangements involving an increasing number of pores, and is related to gel syneresis and aging.

In this talk, I will discuss the issue of gauge fixing for strongly correlated electrons coupled to quantum light, described by projected low-energy models such as those obtained within tight-binding methods. I will present a formalism that allows one to write down the Hamiltonian of correlated electrons coupled to photons in the dipole and Coulomb gauges which remain fully equivalent, i.e., related by a unitary transformation. I will discuss the relation between this approach and the so called Peierls substitution, often used to describe light-matter coupling in tight-binding models. I will apply proposed formalism to a two-band model for an excitonic insulator coupled to a uniform cavity mode. In the dipole gauge the absence of superradiance beyond mean-field theory is confirmed, in accordance with the recent no-go theorem. Furthermore, the excitation spectrum of the model contains non-trivial light-matter entanglement in the form of polariton modes. I will show that the polariton spectrum is the same within the projected dipole and Coulomb gauge, a further demonstration of gauge equivalence. Moreover, I will show that by applying the proposed formalism to a model presenting topological behavior allows for controlling its topological phase transition point.

Les nanoparticules présentent de nombreux avantages par rapport aux sondes moléculaires organiques et sont maintenant couramment utilisées en microscopie. Cependant, lorsqu’on considère la génération de second harmonique (GHS), c’est-à-dire le phénomène optique non linéaire pour lequel deux photons à une fréquence fondamentale sont convertis en un seul photon à la deuxième harmonique, leur réponse peut être plus compliquée. Une raison est leur taille. Pour les nanoparticules plasmoniques, leur forme joue également un rôle important.

Dans cette présentation, je vais montrer comment la taille et la forme jouent un rôle important dans la réponse GHS des nanoparticules. Je vais également montrer comment ces mesures peuvent être effectuées au niveau d’une seule particule.

Au-delà des nanoparticules métalliques, je présenterai une étude expérimentale de la génération de deuxième harmonique de molécules biologiques pour lesquelles la nature cohérente de ce processus permet d’obtenir les symétries de molécules dont la taille est inférieure aux longueurs d’onde utilisées. En particulier, je présenterai les mesures d’hyperpolarisabités des acides aminés aromatiques en solution.

Of all the scenarios for dark matter, one of the most appealing possibilities is that it is made of elementary particles that were in thermal equilibrium in the early universe. I will consider the possible parameter space of such thermal dark matter. The candidates lie in a region in the T'/T vs. m_dm plane, where the hidden sector temperature, T', may differ from that of the Standard Model temperature, T. This domain is bounded by both theoretical and observational constraints. The former includes limits on dark matter candidates that decoupled when relativistic and on those that decoupled when non-relativistic with the largest annihilation cross section allowed by unitarity. The latter concerns big bang nucleosynthesis and free-streaming. To illustrate this classification, I will present a few simplified dark matter scenarios, showing concretely how each fits into the domain.