Ponzano-Regge model revisited I: Gauge fixing, observables and interacting spinning particles

We show how to properly gauge fix all the symmetries of the Ponzano-Regge model for 3D quantum gravity. This amounts to do explicit finite computations for transition amplitudes. We give the construction of the transition amplitudes in the presence of interacting quantum spinning particles. We introduce a notion of operators whose expectation value gives rise to either gauge fixing, introduction of time, or insertion of particles, according to the choice. We give the link between the spin foam quantization and the hamiltonian quantization. We finally show the link between Ponzano-Regge model and the quantization of Chern-Simons theory based on the double quantum group of SU(2)Comment: 48 pages, 15 figure

DMTs and Covid-19 severity in MS: a pooled analysis from Italy and France

We evaluated the effect of DMTs on Covid-19 severity in patients with MS, with a pooled-analysis of two large cohorts from Italy and France. The association of baseline characteristics and DMTs with Covid-19 severity was assessed by multivariate ordinal-logistic models and pooled by a fixed-effect meta-analysis. 1066 patients with MS from Italy and 721 from France were included. In the multivariate model, anti-CD20 therapies were significantly associated (OR = 2.05, 95%CI = 1.39–3.02, p < 0.001) with Covid-19 severity, whereas interferon indicated a decreased risk (OR = 0.42, 95%CI = 0.18–0.99, p = 0.047). This pooled-analysis confirms an increased risk of severe Covid-19 in patients on anti-CD20 therapies and supports the protective role of interferon

Spin foam models for 3-dimensional quantum gravity

This work presents several new results concerning spin foam model for three-dimensional quantum gravity. Starting from Ponzano-Regge and Turaev-Viro models, we realize a gauge fixing of the diffeomorphism symmetry. Then we introduce point particles in these models, realizing a coupling between quantum gravity and matter. Then we present a new mathematical result on the link between Ponzano-Regge invariant and a Chern-Simons invariant constructed from a quantum group obtained as the double of SU(2). We study the asymptotics of 6j and 10j symbols, which correspond to a semi-classical limit of spin foam models in 3 and 4 dimensions. Finally we show it is possible to realize a non-pertubative sum over topologies of quantum gravity amplitudes in a group field theory framework.Cette thèse présente plusieurs résultats nouveaux pour les modèles de mousses de spin pour la gravité quantique en 3 dimensions. A partir des modèles de Ponzano-Regge et Turaev-Viro, nous montrons qu'il est possible de réaliser une fixation de jauge de la symétrie par difféomorphisme. Nous introduisons dans ces modèles des particules ponctuelles pour réaliser ainsi un couplage de ces modèles de gravité quantique à de la matière. Nous présentons un nouveau résultat mathématique sur les liens entre l'invariant de Ponzano-Regge et un invariant de Chern-Simons construit à partir du groupe quantique obtenu comme le double de SU(2). Nous étudions les asymptotiques de symboles 6j et 10j qui correspondent à la limite semi-classique des modèles de mousse de spin en 3 et 4 dimensions. Enfin nous montrons qu'il est possible dans un cas particulier de réaliser une somme non-perturbative sur les topologies des amplitudes de gravité quantique dans un modèle de théorie des champs sur un groupe

Science outreach : from YouTube videos to video games ? - David Louapre

In the past few years, we have seen the rise of the use of internet videos for science outreach, especially through dedicated Youtube channels.&nbsp; In this talk, I'll share my experience in using this media, and discuss how some of its weaknesses, especially the passive&nbsp;attitude of the audience, could be overcome using another media : video games. &nbsp; Biography: David Louapre received his PhD in Theoretical physics, in the field of quantum gravity. He then left academia and spent 15 years in the industry of materials, doing R&amp;D in machine&nbsp;learning and material science. In 2018, he became Scientific director of Ubisoft, one of the leading company developing video games. He owns the successful YouTube channel Science Etonnante.</p

Modèles de mousses de spin pour la gravité quantique en 3 dimensions

LYON-ENS Sciences (693872304) / SudocSudocFranceF

Mais qui a attrapé le bison de Higgs ?: ... et autres questions que vous n'avez jamais osé poser à haute voix

Les premiers hommes, le Big-Bang et le boson de Higgs vous intriguent ? Vous fourmillez de questions sans toujours oser les poser à haute voix ? Ce livre est fait pour vous ! Laissez le créateur de la chaîne YouTube "Science étonnante" (près de 100 000 abonnés) vous révéler ses découvertes préférées. Vous n'avez qu'une vague idée de ce qu'est un atome ? Un gène ? Une probabilité ? Embarquez, vous en savez bien assez

Heat Simulation on Meshless Crafted-Made Shapes

International audienceInteractive shape crafting is an increasingly popular feature in video games, offering players a sense of freedom and personalization. In this work, we propose to combine a stochastic simulation approach to solve the heat equation on Implicit Surface, enabling crafting-ready shapes. Our simulation relies on the "Walk on Sphere" (WoS) approach allowing to solve the asymptotic solution of the heat PDE at any point in space without the need for an explicit mesh structure. To enable interactivity when the shape is moved near a heat source, we propose the integration of time-evolving modifiers. Firstly, using the separation of variables over the PDE enables the approximation of the heating evolution using an additional exponential time variation. Then, we procedurally attach local secondary heat sources to the surface for smooth cool-down. We demonstrate the effectiveness our approach on blended-material shapes generated using CSG operations, combining spatially-varying thermal diffusivity. Overall, our method offers a promising avenue for incorporating often-neglected physical interactions, such as heat-related phenomena, into video games with complex and customizable shapes