Scattering of conformal higher spin fields

We develop a formalism for describing the most general notion of tree-level scattering amplitudes in 4d conformal higher spin theory. As conformal higher spin fields obey higher-derivative equations of motion, there are many distinct on-shell external states which may contribute to their scattering, some of which grow polynomially with time, leading to ill-defined amplitudes. We characterize the set of admissible scattering states which produce finite tree amplitudes, noting that there are more such states than just standard massless higher spins obeying two-derivative equations of motion. We use conformal gravity as a prime example, where the set of scattering states includes the usual Einstein graviton and a `ghost' massless spin 1 particle. An extension of the usual spinor helicity formalism allows us to encode these scattering states efficiently in terms of `twistor-spinors'. This leads to compact momentum space expressions for all finite tree-level 3-point amplitudes of conformal higher spin theory. While some of these 3-point amplitudes vanish (including all those with only standard two-derivative higher spin external states), there are many others which are non-vanishing. We also comment on the generalization to scattering of conformal higher spins in AdS$_4$.Comment: 40 pages, no figures. v2: references adde

Techniques de broyage en pharmacie

National audienc

Techniques de broyage en pharmacie

National audienc

Comparison of various milling technologies for grinding pharmaceutical powders

n° spécial de revue reprenant après révision certains papiers du 10th European Symposium on Comminution/627th Event of the European‐Federation‐of‐Chemical‐Engineering, Heidelberg, GERMANY, SEP 02‐05, 2002International audienceThis paper examines fine grinding techniques in current use in the pharmaceutical industry. Experimental results are given for fine grinding of vitamin C, chosen as a model substance representative of pharmaceutical products, using eight different grinding mills chosen amongst those in current use in the pharmaceutical industry. The results are evaluated in term of product quality expressed as particle size and distribution and also in terms of operating criteria applicable in the pharmaceutical industry such as ease of setting up, ease of cleaning, and investment cost. The main conclusion reinforces and quantifies current practice of using pancake mills that are preferred for ultra fine grinding as they are simple to use, can treat high feed rates and are easy to clean

Mise en évidence de pertes de particules par charge d'espace et d'une anomalie de plan médian dans le synchrotron saturne

Measurements of the number of particles effectively présent in the vacuum chamber before turning RF on (τHF) prove that half on the injected beam is lost on the back of the inflector due to interaction. The causal effect (repulsion of two bunches circulating together) is made evident from the experimental and theoretical point of view ; figure 8 show the important perturbation on the trajectories. The magnetic median plane was at first 0,5 cm too high but it is lower now that a ferromagnetic radiation shielding has been put on the top of the magnet.La mesure du nombre de particules effectivement présentes dans la chambre à l'instant τHF où débute l'accélération a permis de constater que la moitié environ des particules injectées sont perdues sur le dos de l'inflecteur du fait de leur interaction. Le phénomène élémentaire (répulsion de 2 tours circulant ensemble) est étudié expérimentalement et théoriquement ; l'effet important qui en résulte est visualisé par la figure 8. Le plan médian magnétique, trop haut initialement de 0,5 cm, a été abaissé du fait de la présence, au-dessus de l'aimant, d'un plafond ferromagnétique (protection contre le rayonnement)