2D sigma models and differential Poisson algebras

We construct a two-dimensional topological sigma model whose target space is endowed with a Poisson algebra for differential forms. The model consists of an equal number of bosonic and fermionic fields of worldsheet form degrees zero and one. The action is built using exterior products and derivatives, without any reference to any worldsheet metric, and is of the covariant Hamiltonian form. The equations of motion define a universally Cartan integrable system. In addition to gauge symmetries, the model has one rigid nilpotent supersymmetry corresponding to the target space de Rham operator. The rigid and local symmetries of the action, respectively, are equivalent to the Poisson bracket being compatible with the de Rham operator and obeying graded Jacobi identities. We propose that perturbative quantization of the model yields a covariantized differential star product algebra of Kontsevich type. We comment on the resemblance to the topological A model.Comment: 20 page

Une nouvelle méthode multi-élément non-intrusive basée sur la clusterisation agglorémative capable d'approcher les systèmes dynamiques bifurcatifs

International audienceA multi-element non-intrusive generalised polynomial chaos method is developed to approximate state variable of a bifurcative dynamical system. It rely on a partitioning of the stochastic space along discon-tinuities of any shapes, efficient even when the discontinuities are running partially, and allowing the use of a low degree of approximation. An agglomerative clustering method is implemented in a space defined by the values of the quantity of interest (QOI) and of its derivatives with respect to the stochastic parameters. The stochastic space is first properly sampled. Then, at every instant, several partitions of the stochastic space are tested and the best one is selected as the one minimizing the maximum of the cross-validation errors of the local surrogate models. Once the local models are obtained and the sto-chastic space is correctly sliced, a neural network classifier is learned to determine in which element a sample is for further evaluations at the considered instant. The method uses the same samples for the space partitioning and for the training of the local models with regression thus reducing the computational cost. The long-time integration problem is countered and the stochastic space can be split according to the discontinuity induced by the potential bifurcation. The results of the method are advantageously compared to those obtained with the direct use of a Gradient Tree Boosting algorithm at every instant and the classical Pseudo projection method for a system leading to a bifurcation

Affordability and subsidies in public urban transport : what do we mean, what can be done?

Subsidy policies on public urban transport have been adopted ubiquitously. In both developed and developing countries, subsidies are implemented to make transport more affordable. Despite their widespread implementation, there are virtually no quantitative assessments of their distributional incidence, making it impossible to determine if these instruments are pro-poor. This paper reviews the arguments used to justify subsidy policies in public urban transport. Using different tools to quantitatively evaluate the incidence and distributive impacts of subsidy policy options, the paper analyzes the findings of a series of researchpapers that study urban public transport subsidy policies in developed and developing countries. The available evidence indicates that current public urban transport subsidy policies do not make the poorest better off. Supply-side subsidies are, for the most part, neutral or regressive; while demand-side subsidies perform better-although many of them do not improve income distribution. Considering that the policy objective is to improve the welfare of the poorest, it is imperative to move away from supply-side subsidies towards demand-side subsidies and to integrate transport social concerns into wider poverty alleviation efforts, which include the possibility of channeling subsidies through monetary transfer systems or through other transfer instruments (food subsidies, health services and education for the poor). The general conclusion of the paper is that more effort should be devoted to improve the targeting properties of public urban transport subsidies using means-testing procedures to ensure a more pro-poor incidence of subsidies.Transport Economics Policy&Planning,Transport in Urban Areas,Urban Transport,Taxation&Subsidies,Economic Theory&Research

A new stylolite classification scheme to estimate compaction and local permeability variations

This study was carried out within the framework of DGMK (German Society for Petroleum and Coal Science and Technology) research project 718 “Mineral Vein Dynamics Modeling”, which is funded by the companies ExxonMobil Production Deutschland GmbH, GDF SUEZ E&P Deutschland GmbH, DEA Deutsche Erdoel AG and Wintershall Holding GmbH, within the basic research program of the WEG Wirtschaftsverband Erdoel- und Erdgasgewinnung e.V. We thank the companies for their financial support and their permission to publish these results. This work has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no 31688. The Zechstein data were collected with the help of Simon Gast. We thank Jean-Pierre Gratier and an anonymous reviewer for their comments that improved an earlier version of the manuscript.Peer reviewedPostprin

Action principles for higher and fractional spin gravities

We review various off-shell formulations for interacting higher-spin systems in dimensions 3 and 4. Associated with higher-spin systems in spacetime dimension 4 is a Chern-Simons action for a superconnection taking its values in a direct product of an infinite-dimensional algebra of oscillators and a Frobenius algebra. A crucial ingredient of the model is that it elevates the rigid closed and central two-form of Vasiliev's theory to a dynamical 2-form and doubles the higher-spin algebra, thereby considerably reducing the number of possible higher spin invariants and giving a nonzero effective functional on-shell. The two action principles we give for higher-spin systems in 3D are based on Chern-Simons and BF models. In the first case, the theory we give unifies higher-spin gauge fields with fractional-spin fields and an internal sector. In particular, Newton's constant is related to the coupling constant of the internal sector. In the second case, the BF action we review gives the fully nonlinear Prokushkin-Vasiliev, bosonic equations for matter-coupled higher spins in 3D. We present the truncation to a single, real matter field relevant in the Gaberdiel-Gopakumar holographic duality. The link between the various actions we present is the fact that they all borrow ingredients from Topological Field Theory. It has bee conjectured that there is an underlying and unifying 2-dimensional first-quantised description of the previous higher-spin models in 3D and 4D, in the form of a Cattaneo-Felder-like topological action containing fermionic fields.Comment: 41+1 pages. References added and reorganized, corrected typos, last paragraph of section 2 re-written. Contribution to the proceedings of the International Workshop on Higher Spin Gauge Theories (4-6 November 2015, Singapore