Pebble accretion at the origin of water in Europa

Despite the fact that the observed gradient in water content among the Galilean satellites is globally consistent with a formation in a circum-Jovian disk on both sides of the snowline, the mechanisms that led to a low water mass fraction in Europa ($\sim$$8\%$) are not yet understood. Here, we present new modeling results of solids transport in the circum-Jovian disk accounting for aerodynamic drag, turbulent diffusion, surface temperature evolution and sublimation of water ice. We find that the water mass fraction of pebbles (e.g., solids with sizes of 10$^{-2}$ -- 1 m) as they drift inward is globally consistent with the current water content of the Galilean system. This opens the possibility that each satellite could have formed through pebble accretion within a delimited region whose boundaries were defined by the position of the snowline. This further implies that the migration of the forming satellites was tied to the evolution of the snowline so that Europa fully accreted from partially dehydrated material in the region just inside of the snowline.Comment: Accepted for publication in Ap

Structure of Infrared Singularities of Gauge-Theory Amplitudes at Three and Four Loops

The infrared divergences of massless n-parton scattering amplitudes can be derived from the anomalous dimension of n-jet operators in soft-collinear effective theory. Up to three-loop order, the latter has been shown to have a very simple structure: it contains pairwise color-dipole interactions among the external partons, governed by the cusp anomalous dimension and a logarithm of the kinematic invariants s_{ij}, plus a possible three-loop correlation involving four particles, which is described by a yet unknown function of conformal cross ratios of kinematic invariants. This function is constrained by two-particle collinear limits and by the known behavior of amplitudes in the high-energy limit. We construct a class of relatively simple functions satisfying these constraints. We also extend the analysis to four-loop order, finding that three additional four-particle correlations and a single five-particle correlation appear, which again are governed by functions of conformal cross ratios. Our results suggest that the dipole conjecture, which states that only two-particle color-dipole correlations appear in the anomalous dimension, may need to be generalized. We present a weaker form of the conjecture, stating that to all orders in perturbation theory corrections to the dipole formula are governed by functions of conformal cross ratios, and are O(1/N_c^2) suppressed relative to the dipole term. If true, this conjecture implies that the cusp anomalous dimension obeys Casimir scaling to all orders in perturbation theory.Comment: 21 pages, 1 figur

First disk-resolved spectroscopy of (4) Vesta

Vesta, the second largest Main Belt asteroid, will be the first to be explored in 2011 by NASA's Dawn mission. It is a dry, likely differentiated body with spectrum suggesting that is has been resurfaced by basaltic lava flows, not too different from the lunar maria. Here we present the first disk-resolved spectroscopic observations of an asteroid from the ground. We observed (4) Vesta with the ESO-VLT adaptive optics equipped integral-field near-infrared spectrograph SINFONI, as part of its science verification campaign. The highest spatial resolution of ~90 km on Vesta's surface was obtained during excellent seeing conditions (0.5") in October 2004. We observe spectral variations across Vesta's surface that can be interpreted as variations of either the pyroxene composition, or the effect of surface aging. We compare Vesta's 2 micron absorption band to that of howardite-eucrite-diogenite (HED) meteorites that are thought to originate from Vesta, and establish particular links between specific regions and HED subclasses. The overallcomposition is found to be mostly compatible with howardite meteorites, although a small area around 180 deg. East longitude could be attributed to a diogenite-rich spot. We finally focus our spectral analysis on the characteristics of Vesta's bright and dark regions as seen from Hubble Space Telescope's visible and Keck-II's near-infrared images.Comment: 13 pages, 11 figures, 3 table

Next-to-leading power threshold logarithms: a status report

There is ample evidence, dating as far back as Low's theorem, that the universality of soft emissions extends beyond leading power in the soft energy. This universality can, in principle, be exploited to generalise the formalism of threshold resummations beyond leading power in the threshold variable. In the past years, several phenomenological approaches have been partially successful in performing such a resummation. Here, we briefly review some recent developments which pave the way to a solution of this problem, at least for electroweak annihilation processes.Comment: Contribution to the Proceedings of the 12th International Symposium on Radiative Corrections (Radcor 2015) and LoopFest XIV, UCLA, 15-19 June, 201

Approximate NNLO Predictions for the Stop-Pair Production Cross Section at the LHC

If the minimal supersymmetric standard model at scales of around 1 TeV is realized in nature, the total top-squark pair production cross section should be measurable at the CERN Large Hadron Collider. In this work we present precise predictions for this observable, which are based upon approximate NNLO formulas obtained using soft-collinear effective theory methods.Comment: 36 pages, 7 figures and 11 tables. Version published in JHEP 1307 (2013) 04

Combining Parametric and Non-parametric Algorithms for a Partially Unsupervised Classification of Multitemporal Remote-Sensing Images

In this paper, we propose a classification system based on a multiple-classifier architecture, which is aimed at updating land-cover maps by using multisensor and/or multisource remote-sensing images. The proposed system is composed of an ensemble of classifiers that, once trained in a supervised way on a specific image of a given area, can be retrained in an unsupervised way to classify a new image of the considered site. In this context, two techniques are presented for the unsupervised updating of the parameters of a maximum-likelihood (ML) classifier and a radial basis function (RBF) neural-network classifier, on the basis of the distribution of the new image to be classified. Experimental results carried out on a multitemporal and multisource remote-sensing data set confirm the effectiveness of the proposed system

Lo normal y lo político

Las obras de Montesquieu y Durkheim, separadas comúnmente por corrientes disciplinarias, muestran sin embargo importantes coincidencias tanto en los conceptos centrales que desarrollaron como en las aporías que debieron sortear al intentar responder al problema fundador del pensamiento moderno: la irreductible diversidad que caracteriza el mundo humano. Este artículo propone una visión conjunta de sus obras a partir de un análisis paralelo de la noción de conveniencia (convenance) en la obra Montesquieu y de patología social (pathologie sociale) en la obra de Durkheim. Se intenta mostrar asimismo los límites a los que se enfrentó cada una así como los legados que dejaron en la filosofía social contemporánea

NNLL Momentum-Space Resummation for Stop-Pair Production at the LHC

If supersymmetry near the TeV scale is realized in Nature, the pair production of scalar top squarks is expected to be observable at the Large Hadron Collider. Recently, effective field-theory methods were employed to obtain approximate predictions for the cross section for this process, which include soft-gluon emission effects up to next-to-next-to-leading order (NNLO) in perturbation theory. In this work we employ the same techniques to resum soft-gluon emission effects to all orders in perturbation theory and with next-to-next-to-logarithmic (NNLL) accuracy. We analyze the effects of NNLL resummation on the stop-pair production cross section by obtaining NLO+NNLL predictions in pair invariant mass and one-particle inclusive kinematics. We compare the results of these calculations to the approximate NNLO predictions for the cross sections.Comment: 25 pages, 6 figure