Clock spectroscopy of interacting bosons in deep optical lattices

We report on high-resolution optical spectroscopy of interacting bosonic $^{174}$Yb atoms in deep optical lattices with negligible tunneling. We prepare Mott insulator phases with singly- and doubly-occupied isolated sites and probe the atoms using an ultra-narrow "clock" transition. Atoms in singly-occupied sites undergo long-lived Rabi oscillations. Atoms in doubly-occupied sites are strongly affected by interatomic interactions, and we measure their inelastic decay rates and energy shifts. We deduce from these measurements all relevant collisional parameters involving both clock states, in particular the intra- and inter-state scattering lengths

Exploring jet-launching conditions for SFXTs

In the magneto-centrifugal mechanism for jet formation, accreting neutron stars are assumed to produce relativistic jets only if their surface magnetic field is weak enough ($B \sim 10^8$ G). However, the most common manifestation of neutron stars are pulsars, whose magnetic field distribution peaks at $B \sim 10^{12}$ G. If the neutron star magnetic field has at least this strength at birth, it must decay considerably before jets can be launched in binary systems. We study the magnetic field evolution of a neutron star that accretes matter from the wind of a high-mass stellar companion so that we can constrain the accretion rate and the impurities in the crust, which are necessary conditions for jet formation. We solved the induction equation for the diffusion and convection of the neutron star magnetic field confined to the crust, assuming spherical accretion in a simpliflied one-dimensional treatment. We incorporated state-of-the-art microphysics, including consistent thermal evolution profiles, and assumed two different neutron star cooling scenarios based on the superfluidity conditions at the core. We find that in this scenario, magnetic field decay at long timescales is governed mainly by the accretion rate, while the impurity content and thermal evolution of the neutron star play a secondary role. For accretion rates $\dot{M}\gtrsim10^{-10}$ M$_{\odot}$ yr$^{-1}$, surface magnetic fields can decay up to four orders of magnitude in $\sim$10$^7$ yr, which is the timescale imposed by the evolution of the high-mass stellar companion in these systems. Based on these results, we discuss the possibility of transient jet-launching in strong wind-accreting high-mass binary systems like supergiant fast X-ray transients.Comment: 8 pages, 8 figures. Accepted for publication in A&

Vertex adjacencies in the set covering polyhedron

We describe the adjacency of vertices of the (unbounded version of the) set covering polyhedron, in a similar way to the description given by Chvatal for the stable set polytope. We find a sufficient condition for adjacency, and characterize it with similar conditions in the case where the underlying matrix is row circular. We apply our findings to show a new infinite family of minimally nonideal matrices.Comment: Minor revision, 22 pages, 3 figure

El tema de la muerte en la literatura oral Kawésqar (Alacalufe)

De la literatura oral de los pueblos fueguinos la más desconocida es la de los kawésqar, etnia que habita el extremo sur de Chile, y que se cuenta entre las más antiguas de las que poblaron el confin austral del continente. Este artículo presenta algunos textos miticos sobre la muerte, transmitidos oralmente y rescatados por el autor en trabajos de terreno. En estos textos se examina el tema de la muerte en relación con el sueño, y de las relaciones entre los mundos mítico y real. Se establece, asimismo, una clasificación de los relatos, sobre la base de una tipologia de la muerte.