Tools for NLO automation: extension of the golem95C integral library

We present an extension of the program golem95C for the numerical evaluation of scalar integrals and tensor form factors entering the calculation of one-loop amplitudes, which supports tensor ranks exceeding the number of propagators. This extension allows various applications in Beyond the Standard Model physics and effective theories, for example higher ranks due to propagators of spin two particles, or due to effective vertices. Complex masses are also supported. The program is not restricted to the Feynman diagrammatic approach, as it also contains routines to interface to unitarity-inspired numerical reconstruction of the integrand at the tensorial level. Therefore it can serve as a general integral library in automated programs to calculate one-loop amplitudes.Comment: 17 pages, 1 figure, the program can be downloaded from http://golem.hepforge.org/95/. arXiv admin note: substantial text overlap with arXiv:1101.559

Penetration and cratering experiments of graphite by 0.5-mm diameter steel spheres at various impact velocities

Cratering experiments have been conducted with 0.5-mm diameter AISI 52100 steel spherical projectiles and 30-mm diameter, 15-mm long graphite targets. The latter were made of a commercial grade of polycrystalline and porous graphite named EDM3 whose behavior is known as macroscopically isotropic. A two-stage light-gas gun launched the steel projectiles at velocities between 1.1 and 4.5 km s 1. In most cases, post-mortem tomographies revealed that the projectile was trapped, fragmented or not, inside the target. It showed that the apparent crater size and depth increase with the impact velocity. This is also the case of the crater volume which appears to follow a power law significantly different from those constructed in previous works for similar impact conditions and materials. Meanwhile, the projectile depth of penetration starts to decrease at velocities beyond 2.2 km s 1. This is firstly because of its plastic deformation and then, beyond 3.2 km s 1, because of its fragmentation. In addition to these three regimes of penetration behavior already described by a few authors, we suggest a fourth regime in which the projectile melting plays a significant role at velocities above 4.1 km s 1. A discussion of these four regimes is provided and indicates that each phenomenon may account for the local evolution of the depth of penetration

Extreme-value statistics of stochastic transport processes

We derive exact expressions for the finite-time statistics of extrema (maximum and minimum) of the spatial displacement and the fluctuating entropy flow of biased random walks. Our approach captures key features of extreme events in molecular motor motion along linear filaments. For one-dimensional biased random walks, we derive exact results which tighten bounds for entropy production extrema obtained with martingale theory and reveal a symmetry between the distribution of the maxima and minima of entropy production. Furthermore, we show that the relaxation spectrum of the full generating function, and hence of any moment, of the finite-time extrema distributions can be written in terms of the Marcenko-Pastur distribution of random-matrix theory. Using this result, we obtain efficient estimates for the extreme-value statistics of stochastic transport processes from the eigenvalue distributions of suitable Wishart and Laguerre random matrices. We confirm our results with numerical simulations of stochastic models of molecular motors

Polarization measurements analysis II. Best estimators of polarization fraction and angle

With the forthcoming release of high precision polarization measurements, such as from the Planck satellite, it becomes critical to evaluate the performance of estimators for the polarization fraction and angle. These two physical quantities suffer from a well-known bias in the presence of measurement noise, as has been described in part I of this series. In this paper, part II of the series, we explore the extent to which various estimators may correct the bias. Traditional frequentist estimators of the polarization fraction are compared with two recent estimators: one inspired by a Bayesian analysis and a second following an asymptotic method. We investigate the sensitivity of these estimators to the asymmetry of the covariance matrix which may vary over large datasets. We present for the first time a comparison among polarization angle estimators, and evaluate the statistical bias on the angle that appears when the covariance matrix exhibits effective ellipticity. We also address the question of the accuracy of the polarization fraction and angle uncertainty estimators. The methods linked to the credible intervals and to the variance estimates are tested against the robust confidence interval method. From this pool of estimators, we build recipes adapted to different use-cases: build a mask, compute large maps, and deal with low S/N data. More generally, we show that the traditional estimators suffer from discontinuous distributions at low S/N, while the asymptotic and Bayesian methods do not. Attention is given to the shape of the output distribution of the estimators, and is compared with a Gaussian. In this regard, the new asymptotic method presents the best performance, while the Bayesian output distribution is shown to be strongly asymmetric with a sharp cut at low S/N.Finally, we present an optimization of the estimator derived from the Bayesian analysis using adapted priors

Effect of the clearfelling on the water quality: Example of a spruce forest on a small catchment in France

This paper presents the variation of the hydrology and the water quality of a spruce catchment, located at Mont-Lozére (France), in a mediterranean mountain climate area , in relation to the forest status during 12 years (1981-1993). Four situations were successively examined : healthy forest (1981-84), declining stand with pest (1984-87), gradual clearfelling (1987-89) and reforestation (1989-93). An undisturbed beech catchment was used to provide reference values. In the hydrological budgets, the P-Q value (as ETR) was slightly higher in the spruce catchment than in the beech one during the first period and decreased progressively in the following ones as a consequence of: (1) the declining stand of the forest and (2) the clearfelling. No change was observed for cations, and NO3 concentrations remained were very low during the whole period in the streamwater of the beech catchment , in relation to the steady state of that ecosystem. Iin the spruce catchment,the concentrations of cations and NO, were always higher, and increased slightly during the disease. During the clearfelling, NO3 was strongly related to Ca and Mg. Six months after the reforestation, NO,, Ca , Mg concentrations were respectively 11,9 , 2,6 and 3,6 higher than at the begiming of the clearfelling.They retumed to previous values at the end of 1993. The Input-Output budget of cations presented a continuous storage in the beech catchment and simultanously a permanent release in the spruce catchment . The mean loss, -expressed as the denudation cation rate, in keq.ha-1.year-1 was as follow: -0,41 (1981-84), -0,65 (1984-87), -1,60 (1987-89) and -0,82 (1989-93).The leaching was observed during more than 6 years after the clearfelling, resulting probably from the duration of the drought period , and from the mineralization of the remaining important organic matter comparhnen

Local disorder and optical properties in V-shaped quantum wires : towards one-dimensional exciton systems

The exciton localization is studied in GaAs/GaAlAs V-shaped quantum wires (QWRs) by high spatial resolution spectroscopy. Scanning optical imaging of different generations of samples shows that the localization length has been enhanced as the growth techniques were improved. In the best samples, excitons are delocalized in islands of length of the order of 1 micron, and form a continuum of 1D states in each of them, as evidenced by the sqrt(T) dependence of the radiative lifetime. On the opposite, in the previous generation of QWRs, the localization length is typically 50 nm and the QWR behaves as a collection of quantum boxes. These localization properties are compared to structural properties and related to the progresses of the growth techniques. The presence of residual disorder is evidenced in the best samples and explained by the separation of electrons and holes due to the large in-built piezo-electric field present in the structure.Comment: 8 figure

Etude et modélisation hydropédologique d'un bassin versant de la zone sahélo-soudanienne au Burkina-Faso (utilisation du modèle "SOURCE")

Cette thèse a pour objectif la mise au point d'une modélisation hydropédologique d'un bassin versant préalable à une modélisation des comportements hydriques de ce bassin. Les conceptions de la modélisation hydrologique sont traditionnellement orientées vers la recherche des crues maximales pour les études d'ouvrages d'art. Elles ont cependant évolué et se préoccupent également aujourd'hui d'étudier les phénomènes plus globalement en étudiant les besoins en eau des cultures et l'assainissement des sols. Nous exposons les principes et le fonctionnement théorique d'un modèle hydropédologique spatialisé. Il intègre les différenciations spatiales du fonctionnement hydrique des sols d'un paysage restreint pour les besoins de l'expérimentation à un bassin versant. Il permettra d'étudier la gestion des bilans d'eau d'une aire de réception des précipitations et d'évaluer sa contribution au ruissellement à la redistribution de l'eau dans le sol et vers la nappe et à sa consommation par la végétation. Nous aborderons les concepts de base, la modélisation de la couverture pédologique en organisation de volumes hydropédologiques, la spatialisation du système pédologique, le fonctionnement hydrodynamique dans le temps et l'espace et l'ensemble des fonctions de transfert propres au transfert hydrique dans les sols. L'étude de terrain qui permet d'établir cette modélisation recouvre la caractérisation physique du milieu. On établit une base d'informations concernant le milieu physique d'un bassin versant du Nord Burkina Faso en zone climatique sahélo-soudanienne, de substrat granitique fissuré. Puis nous poursuivrons cette description générale par une approche plus précise de l'hydrologie du bassin versant: l'hydrographie, les fonctionnements hydrologiques élémentaires des surfaces caractéristiques des aires contributives, et le comportement hydrique naturel des sols. La télédétection, l'analyse d'images permettent une bonne compréhension des répartitions spatiales des classes d'états de surface et constituent un préalable utile à la modélisation. L'étude du milieu pédologique, présente trois phases: Une étude générale des organisations pédologiques du bassin et des principales caractéristiques des sols. Une étude du milieu poreux et des propriétés hydriques des volumes du sol. La typologie des volumes hydropédologiques et leurs classifications en volumes caractérisés par leurs propriétés propres au transfert et au stockage d'eau. Cette modélisation en volumes hydropédologiques donne lieu à la compartimentation de la couverture pédologique aboutissant à un bassin composé de 17 séquences de volumes hydropédologiques de référence. L'ensemble des données du système d'information réunies au travers de la modélisation de la couverture pédologique, des états de surfaces et de l'étude des propriétés hydropédologiques constitue la base de données physique du milieu. Le modèle "SOURCE" modélise dans le temps et l'espace le devenir de l'eau entrant dans le système. On en examine la cohérence des résultats, dans l'état actuel de son développement, en critiquant les informations issues du modèle sous la forme de chroniques de lames ruisselées et d'évapotranspiration, de profils d'eau stockée: - au niveau de parcelles agronomiques expérimentales constituant des micro bassins versants. - au niveau du bassin versant de 3 km2. La modélisation du bassin versant sur deux années contrastées permet généralement de confirmer les résultats obtenus, sur les parcelles, par ce modèle et d'en évaluer assez clairement les limites. Nous concluons sur les améliorations à apporter au modèle. (Résumé d'auteur

A compact representation of the 2 photon 3 gluon amplitude

A compact representation of the loop amplitude gamma gamma ggg -> 0 is presented. The result has been obtained by using helicity methods and sorting with respect to an irreducible function basis. We show how to convert spinor representations into a field strength representation of the amplitude. The amplitude defines a background contribution for Higgs boson searches at the LHC in the channel H -> gamma gamma + jet which was earlier extracted indirectly from the one-loop representation of the 5-gluon amplitude.Comment: 15 pages Latex, 6 eps files included, revised versio