Single top polarisation as a window to new physics

We discuss the effect of heavy new physics, parameterised in terms of four-fermion operators, in the polarisation of single top (anti-)quarks in the $t$-channel process at the LHC. It is found that for operators involving a right-handed top quark field the relative effect on the longitudinal polarisation is twice larger than the relative effect on the total cross section. This enhanced dependence on possible four-fermion contributions makes the polarisation measurements specially interesting, in particular at high momenta.Comment: LaTeX 10 pages. v2: comments and references added, journal versio

Quantification of uncertainty in the prediction of railway induced ground vibration due to the use of statistical track unevenness data

Versión PostprintEnvironmental vibrations due to railway traffic are predominantly due to dynamic axle loads caused by wheel and track unevenness and impact excitation by rail joints and wheel flats. Because of its irregular character, track unevenness is commonly processed statistically and represented by its power spectral density function or its root mean square (RMS) value in one-third octave bands. This statistical description does not uniquely define the track unevenness at a given site, however, and different track unevenness profiles matching the statistical description will lead to different predictions of dynamic axle loads and resulting ground vibration. This paper presents a methodology that allows quantifying the corresponding variability in ground vibration predictions. The procedure is derived assuming the geometry of the track and soil to be homogeneous along the track. The procedure is verified by means of Monte Carlo simulations and its usefulness for assessing the mismatch between predicted and measured ground vibrations is demonstrated in a case study. The results show that the response in time domain and its narrow band spectrum exhibit significant variability which is reduced when the running RMS value or the one-third octave band spectrum of the response is considered.Ministerio de Economía y Competitividad BIA2010-1484

A 2.5D coupled FE-BE model for the prediction of railway induced vibrations

Ground vibrations induced by railway traffic at grade and in tunnels are often studied by means of two-and-half dimensional (2.5D) models that are based on a Fourier transform of the coordinate in the longitudinal direction of the track. In this paper, the need for 2.5D coupled finite element-boundary element models is demonstrated in two cases where the prediction of railway induced vibrations is considered. A recently proposed novel 2.5D methodology is used where the finite element method is combined with a boundary element method, based on a regularized boundary integral equation. In the formulation of the boundary integral equation, Green's functions of a layered elastic halfspace are used, so that no discretization of the free surface or the layer interfaces is required. In the first case, two alternative models for a ballasted track on an embankment are compared. In the first model, the ballast and the embankment are modelled as a continuum using 2.5D solid elements, whereas a simplified beam representation is adopted in the second model. The free field vibrations predicted by both models are compared to those measured during a passage of the TGVA at a site in Reugny (France). A very large difference is found for the free field response of both models that is due to the fact that the deformation of the cross section of the embankment is disregarded in the simplified representation. In the second case, the track and free field response due to a harmonic load in a tunnel embedded in a layered halfspace are considered. A simplified methodology based on the use of the full space Green's function in the tunnel–soil interaction problem is investigated. It is shown that the rigorous finite element-boundary element method is required when the distance between the tunnel and the free surface and the layer interfaces of the halfspace is small compared to the wavelength in the soil.Junta de Andalucía IAC08-II-3343Ministerio de Educación y Ciencia JC2008-0013

GoSam: A program for automated one-loop Calculations

The program package GoSam is presented which aims at the automated calculation of one-loop amplitudes for multi-particle processes. The amplitudes are generated in terms of Feynman diagrams and can be reduced using either D-dimensional integrand-level decomposition or tensor reduction, or a combination of both. GoSam can be used to calculate one-loop corrections to both QCD and electroweak theory, and model files for theories Beyond the Standard Model can be linked as well. A standard interface to programs calculating real radiation is also included. The flexibility of the program is demonstrated by various examples.Comment: 10 pages, Talk given at the International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT), Uxbridge, London, September 201

Livelihoods of households living near Yangambi Biosphere Reserve, Democratic Republic of Congo

This brief presents findings from an assessment of rural livelihood systems around the reserve. The assessment was undertaken to identify entry points to create wealth, improve nutrition and conserve the forest. It aims to develop a contextual understanding of rural communities and offer a localized frame for development action, by using a cost-effective and integrative household appraisal tool, known as the Rural Household Multi-Indicator Survey (box 1). The narrative is structured around key components of livelihood and farming systems: demographic characteristics and decision-making, farming activities, forest resources, food and nutrition security; and household wealth and wellbeing. These insights serve as touchstone for identifying and planning locally-relevant development investments, as well as for monitoring and evaluation of interventions in the area

Les moyens de subsistance des ménages vivant à proximité de la réserve de la biosphère de Yangambi, République Démocratique du Congo

Cette note présente les résultats d'une évaluation des systèmes de subsistance en milieu rural autour de la réserve. L'évaluation a été entreprise pour identifier les points d'entrée pour créer de la richesse, améliorer la nutrition et protéger la forêt. Il vise à développer une compréhension contextuelle des communautés rurales et à offrir un cadre localisé pour les actions de développement, en utilisant un outil d'évaluation du ménage économique et intégré, appelé Enquête Multi-Indicateurs auprès des Ménages Ruraux (encadré 1). Le récit est structuré autour d'éléments clés des moyens de subsistance et des systèmes agricoles: caractéristiques démographiques et prise de décision, activités agricoles, ressources forestières, sécurité alimentaire et nutritionnelle, la richesse et le bien-être des ménages. Ces informations servent de référence pour identifier et planifier les investissements de développement pertinents au niveau local, ainsi que pour le suivi et l'évaluation des interventions dans la régio

The fictitious force method for efficient calculation of vibration from a tunnel embedded in a multi-layered half-space

This paper presents an extension of the Pipe-in-Pipe (PiP) model for calculating vibrations from underground railways that allows for the incorporation of a multi-layered half-space geometry. The model is based on the assumption that the tunnel displacement is not influenced by the existence of a free surface or ground layers. The displacement at the tunnel–soil interface is calculated using a model of a tunnel embedded in a full space with soil properties corresponding to the soil in contact with the tunnel. Next, a full space model is used to determine the equivalent loads that produce the same displacements at the tunnel–soil interface. The soil displacements are calculated by multiplying these equivalent loads by Green׳s functions for a layered half-space. The results and the computation time of the proposed model are compared with those of an alternative coupled finite element–boundary element model that accounts for a tunnel embedded in a multi-layered half-space. While the overall response of the multi-layered half-space is well predicted, spatial shifts in the interference patterns are observed that result from the superposition of direct waves and waves reflected on the free surface and layer interfaces. The proposed model is much faster and can be run on a personal computer with much less use of memory. Therefore, it is a promising design tool to predict vibration from underground tunnels and to assess the performance of vibration countermeasures in an early design stage.Engineering and Physical Sciences Research Council - grant # [EP/K006665/1]