The dimensional quantum electrodynamics with massless fermions is studied in a covariant gauge. The main new ingredient is an operator solution of the Dirac equation expressed directly in terms of fields present in the original Lagrangian. This permits us analyze in detail residual gauge symmetry present in the covariant gauge. For the sake of a comparison, we study first an analogous solution in a non-gauge Thirring-Wess model and its implications for the axial anomaly arising from the necessity to correctly define products of fermion operators via point splitting. In the Schwinger model, one has to define currents in a gauge invariant way. Certain problems with the usual definition of the vector and axial-vector currents are identified that obscure the origin of massive gauge boson (Schwinger mechanism). We reformulate the model in a finite volume, defining the currents correctly, and clarify the role of the gauge zero mode in the axial anomaly and in the Schwinger mechanism.

Je ferai une revue des différentes méthodes utilisées pour le calcul de fonctions de corrélation à trois et quatre points en théorie de Liouville, des résultats obtenus et des problèmes qui pour moi restent ouverts.

Flavour changing interactions must arise among charged leptons because neutrinos have mass. I briefly review current bounds on various Lepton Flavour Violating processes (in particular Z decays such as Z-> tau^+ mu^-), and some relations among them. Then I argue that the LHC with current data has sensitivity to LFV Z decays beyond the LEP1 bounds.

After a brief overview of the recent experimental results on SUSY searches, I will focus on the so called "Natural Supersymmetry" spectrum and its relation with the observed scalar particle. In particular, motivated by naturalness arguments, I will extend the MSSM in such a way to have a small amount of fine-tuning in the theory and still be compatible with the experimental results.

We consider correlation functions of the form <vac|O|vac>', where |vac> is the vacuum eigenstate of an infinite antiferromagnetic XXZ chain, |vac>' is the vacuum eigenstate of an infinite XXZ chain which is split in two, and O is a local operator. The Hamiltonian of the split chain has no coupling between sites 1 and 0 and arises from a tensor product of left and right boundary transfer matrices. We find a simple, exact expression for <vac|vac>' and an exact integral expression for general <vac|O|vac>' using the vertex operator approach. We compute the integral when O = \sigma^z and find a conjectural expression that is analogous to the known formula for the XXZ spontaneous magnetisation and reduces to it when the boundary magnetic field is zero. We show that correlation functions obey a boundary qKZ equation of a different level to the infinite XXZ chain with one boundary. One application is that the bipartite fidelity f=|<vac|vac>'|^2 provides a measure of quantum entanglement of a bipartite system. The scaling form of -ln(f) is computed and shown to be consistent with a conjectured universal form c/8 log(xi) involving the central charge c and correlation length xi.

Il est généralement admis que les phénomènes quantiques reflètent intrinsèquement un indéterminisme fondamental. La mécanique quantique Bohmienne fournit un antidote à ce consensus! Je présenterai les postulats de cette mécanique et la manière dont son contenu déterministe cohabite avec l'élément statistique, menant, dans le cas non-relativiste, à des prédictions équivalentes à celles de la mécanique quantique orthodoxe. Cette dernière est un algorithme effectif dont les habituelles difficultés conceptuelles disparaissent complètement dans l'approche Bohmienne. J'aborderai enfin, brièvement, ce que je crois le plus pertinent dans cette approche: la possibilité d'une physique s'écartant des phénomènes quantiques standard, et l'enjeu de la construction d'une théorie relativiste des champs.

Les situations d'équilibre, dans lesquelles fluctuations temporelles et réponse à une (petite) perturbation extérieure se confondent, ne sont pas le lot commun des systèmes vivants. Après avoir décrit des "extensions" récentes théorème de fluctuation-dissipation en dehors de l'équilibre, je proposerai une situation physique où l'on peut tirer profit de ces nouveaux résultants, la plupart du temps très formels. Il s'agit du cas d'une bille attachée à la membrane d'une cellule musculaire, utilisée pour sonder les propriétés physiques du cytosquelettes. Travail réalisé en collaboration avec P. Bohec, F. Gallet, C. Maes, P. Visco.

Particle-stabilized emulsions, also called Pickering emulsions, are surfactant-free
metastable dispersions of two non-miscible fluids like oil and water. These emulsions are
kinetically stabilized by colloidal particles partially wetted by the two fluids.
This study aims at understanding the interfacial stabilization mechanisms as well as the links between the interfacial and macroscopic properties of emulsions. In this context, our strategy consists in using colloidal particles (silica, core-shell latexes, microgels) for which characteristics can be continuously tuned either during the synthesis (variation of the particles’ wettability or deformability) or in situ by using a stimulus (pH, salt, temperature…).
Emulsions stabilized by such particles are stimuli responsive and their destabilization can be triggered on demand. We study and report the mechanisms of particle adsorption, the interactions between particles anchored at interfaces and the resulting properties of emulsions.
Such study allows us to draw general concepts governing the emulsions
stabilization/destabilization and to control their end-use properties via the formulation or the emulsification process (temperature, shear).
Colloidal particle stabilized-emulsions can be used as templates to synthesize more
complex materials as illustrated by the elaboration of capsules allowing a thermally controlled delivery of their content or by the production of tailored silica macrocellular foams.