Top production at the LHC: the impact of PDF uncertainties and correlations

In this contribution we discuss the impact of PDF uncertainties on t\bar{t} and t-channel single-top production at the LHC. We present predictions for total cross-sections computed at NLO accuracy with different PDF sets. For single- top production, we point out that the uncertainty arising from the choice of the bottom quark mass is one of the dominant theoretical uncertainties on the total cross-section. Finally, the possibility of using PDF induced correlations between top quark and electroweak vector boson production cross-sections to improve the accuracy of LHC measurements is investigated.Comment: 8 pages, 5 figures. To appear in the Proceedings of the International Workshop on Top Quark Physics (top2010), Bruges, Belgium, May 31 - June 4, 201

An extensive survey of the estimation of uncertainties from missing higher orders in perturbative calculations

We consider two approaches to estimate and characterise the theoretical uncertainties stemming from the missing higher orders in perturbative calculations in Quantum Chromodynamics: the traditional one based on renormalisation and factorisation scale variation, and the Bayesian framework proposed by Cacciari and Houdeau. We estimate uncertainties with these two methods for a comprehensive set of more than thirty different observables computed in perturbative Quantum Chromodynamics, and we discuss their performance in properly estimating the size of the higher order terms that are known. We find that scale variation with the conventional choice of varying scales within a factor of two of a central scale gives uncertainty intervals that tend to be somewhat too small to be interpretable as 68% confidence-level-heuristic ones. We propose a modified version of the Bayesian approach of Cacciari and Houdeau which performs well for non-hadronic observables and, after an appropriate choice of the relevant expansion parameter for the perturbative series, for hadronic ones too.Comment: 34 pages, 24 figure

Compte rendu de "Les os, les cendres et l'Etat" par ESQUERRE, Arnaud, Paris, Fayard, 2011

L'ouvrage d’Arnaud Esquerre participe de ce que l’on peut considérer comme une tentative française de refondation de ce qui a été traditionnellement appelé « sociologie de la mort ». L’auteur prend soin de préciser le caractère trouble d’une notion comme la mort et préfère s’intéresser à un objet concret, matériellement situable par le chercheur et visé par le droit : les restes humains [Premières lignes]

Le retour permanent : communiquer l'enquête en situation d'ethnographie réflexive

Un séjour prolongé sur le terrain peut provoquer des demandes de retour de la part des enquêtés, en même temps que le chercheur y tisse des liens personnels forts. Pour y faire face, la réflexivité permet de comprendre la place du chercheur dans le groupe étudié et de définir le point de vue à travers lequel l’enquête est restituée. Plutôt que d’expertiser, il est possible de discuter des avancées et des orientations de la recherche directement avec les enquêtés, tout en respectant l’objectif de compréhension et les modalités d’accueil de l’ethnographe dans le groupe étudié. Au cours d’interactions routinières, l’enquêteur pré-positionne son analyse en faisant part de l’évolution de sa recherche notamment lorsque se modifie sa perception du terrain, et donc la place qu’il y occupe

Rank-based multi-scale entropy analysis of heart rate variability

The method of MultiScale Entropy (MSE) is an invaluable tool to quantify and compare the complexity of physiological time series at different time scales. Although MSE traditionally employs sample entropy to measure the unpredictability of each coarse-grained series, the same framework can be applied to other metrics. Here we investigate the use of a rank-based entropy measure within the MSE framework. Like in the traditional method, the series are studied in an embedding space of dimension m. The novel entropy assesses the unpredictability of the series quantifying the "amount of shuffling" that the ranks of the mutual distances between pairs of m-long vectors undergo when considering the next observation. The algorithm was tested on recordings from the Fantasia database in a time-varying fashion using non-overlapping 300-samples windows. The method was able to find statistically significant differences between young and healthy elderly subjects at 7 scales/time-windows after accounting for multiple comparisons using the Holm-Bonferroni correction. These promising results suggest the possibility of using this measure to perform a time-varying assessment of complexity with increased accuracy and temporal resolution