Liberating Efimov physics from three dimensions

When two particles attract via a resonant short-range interaction, three particles always form an infinite tower of bound states characterized by a discrete scaling symmetry. It has been considered that this Efimov effect exists only in three dimensions. Here we review how the Efimov physics can be liberated from three dimensions by considering two-body and three-body interactions in mixed dimensions and four-body interaction in one dimension. In such new systems, intriguing phenomena appear, such as confinement-induced Efimov effect, Bose-Fermi crossover in Efimov spectrum, and formation of interlayer Efimov trimers. Some of them are observable in ultracold atom experiments and we believe that this study significantly broadens our horizons of universal Efimov physics.Comment: 17 pages, 5 figures, contribution to a special issue of Few-Body Systems devoted to Efimov Physic

Influence of self-gravity on the runaway instability of black hole-torus systems

Results from the first fully general relativistic numerical simulations in axisymmetry of a system formed by a black hole surrounded by a self-gravitating torus in equilibrium are presented, aiming to assess the influence of the torus self-gravity on the onset of the runaway instability. We consider several models with varying torus-to-black hole mass ratio and angular momentum distribution orbiting in equilibrium around a non-rotating black hole. The tori are perturbed to induce the mass transfer towards the black hole. Our numerical simulations show that all models exhibit a persistent phase of axisymmetric oscillations around their equilibria for several dynamical timescales without the appearance of the runaway instability, indicating that the self-gravity of the torus does not play a critical role favoring the onset of the instability, at least during the first few dynamical timescales.Comment: To appear on Phys.Rev.Let

Quantizing Majorana Fermions in a Superconductor

A Dirac-type matrix equation governs surface excitations in a topological insulator in contact with an s-wave superconductor. The order parameter can be homogenous or vortex valued. In the homogenous case a winding number can be defined whose non-vanishing value signals topological effects. A vortex leads to a static, isolated, zero energy solution. Its mode function is real, and has been called "Majorana." Here we demonstrate that the reality/Majorana feature is not confined to the zero energy mode, but characterizes the full quantum field. In a four-component description a change of basis for the relevant matrices renders the Hamiltonian imaginary and the full, space-time dependent field is real, as is the case for the relativistic Majorana equation in the Majorana matrix representation. More broadly, we show that the Majorana quantization procedure is generic to superconductors, with or without the Dirac structure, and follows from the constraints of fermionic statistics on the symmetries of Bogoliubov-de Gennes Hamiltonians. The Hamiltonian can always be brought to an imaginary form, leading to equations of motion that are real with quantized real field solutions. Also we examine the Fock space realization of the zero mode algebra for the Dirac-type systems. We show that a two-dimensional representation is natural, in which fermion parity is preserved.Comment: 26 pages, no figure

Toshisada Nishida (1941–2011): Chimpanzee Rapport

Frans de Waal pays tribute to pioneering primatologist Toshisada Nishida, who transformed our understanding of chimpanzee behavior and culture and galvanized efforts to ensure their conservation

Landscape analysis – Assessing countries' readiness to scale up nutrition actions in the WHO African region

The purpose of this paper is to describe the use of the Landscape Analysis to assess strengths and weaknesses in combating malnutrition in Sub-Saharan Africa. The Landscape Analysis is an inter-agency initiative to assess gaps and constraints and to identify opportunities for effective nutrition actions in order to accelerate intersectoral action for improving nutrition. In-depth Country Assessments to evaluate countries' "readiness" to scale up nutrition action have been conducted since 2008 in Sub-Saharan Africa. "Readiness" was assessed in terms of the  commitment and capacity of each country and the focus was high stunting burden countries. The main focus was countries with heavy burden of undernutrition. From 2008 to September 2011, a total of 14 countries had undertaken the Landscape Analysis Country Assessment. Nine of them were in Africa: Burkina Faso, Comoros, Cote d’Ivoire, Ethiopia, Ghana, Madagascar, Mali, Mozambique, and South Africa. Three additionalcountries (Guinea, Namibia and Tanzania) were also planning to complete the Landscape Analysis Country Assessment in early 2012.From the findings in the nine countries, the following recommendations have beenmade:• Existing nutrition architectures and coordination mechanisms should bestrengthened and better utilized;• Nutrition needs to be mainstreamed and integrated in relevant sector policies;• Advocacy at high levels is needed to highlight the importance of the lifecourseperspective, focusing particularly on nutrition interventions frompreconception until the first two years of life;• National nutrition policies need to be translated into programmatic actions;• Human resource capacity for public health nutrition needs to be built with highquality in-service trainings in the short-term and long-term strategies toprovide pre-service trainings;• Community-based outreach should be strengthened by using existingchannels;• National nutrition surveillance systems need to be strengthened to ensure adequate use of data for monitoring, evaluation, and planning purposes.As part of the implementation of the 2010 World Health Assembly resolution on Infant and Young Child Nutrition (WHA 63.23) WHO has proposed a process to help countries in developing scale-up plans, which incorporates the Landscape Analysis Country Assessment as a tool to help countries in undertaking the initial context mapping. The countries that have already undertaken an in-depth Country Assessment, such as the Landscape Analysis Country Assessment, are ready to move forward in implementing the next steps in developing scaling-up plans to accelerateaction in nutrition. At the same time, WHO will support additional countries that have expressed interest in conducting the Country Assessment

Counting Majorana zero modes in superconductors

A counting formula for computing the number of (Majorana) zero modes bound to topological point defects is evaluated in a gradient expansion for systems with charge-conjugation symmetry. This semi-classical counting of zero modes is applied to some examples that include graphene and a chiral p-wave superconductor in two-dimensional space. In all cases, we explicitly relate the counting of zero modes to Chern numbers.Comment: 21 pages, 3 figure

Breakdown of smoothness for the Muskat problem

In this paper we show that there exist analytic initial data in the stable regime for the Muskat problem such that the solution turns to the unstable regime and later breaks down i.e. no longer belongs to $C^4$.Comment: 93 pages, 10 figures (6 added

Detection of arcs in Saturn's F ring during the 1995 Sun ring-plane crossing

Observations of the November 1995 Sun crossing of the Saturn's ring-plane made with the 3.6m CFH telescope, using the UHAO adaptive optics system, are presented here. We report the detection of four arcs located in the vicinity of the F ring. They can be seen one day later in HST images. The combination of both data sets gives accurate determinations of their orbits. Semi-major axes range from 140020 km to 140080 km, with a mean of 140060 +- 60 km. This is about 150 km smaller than previous estimates of the F ring radius from Voyager 1 and 2 data, but close to the orbit of another arc observed at the same epoch in HST images.Comment: 8 pages, 3 figures, 1 table, To appear in A&A, for comments : [email protected]