68,399 research outputs found
Stability of the superfluid state in a disordered 1D ultracold fermionic gas
We study a 1D Fermi gas with attractive short range-interactions in a
disordered potential by the density matrix renormalization group (DMRG)
technique. This setting can be implemented experimentally by using cold atom
techniques. We identify a region of parameters for which disorder enhances the
superfluid state. As disorder is further increased, global superfluidity
eventually breaks down. However this transition occurs before the transition to
the insulator state takes place. This suggests the existence of an intermediate
metallic `pseudogap' phase characterized by strong pairing but no quasi
long-range order.Comment: 5 pages, 5 figure
The white dwarf population within 40 pc of the Sun
The white dwarf luminosity function is an important tool to understand the
properties of the Solar neighborhood, like its star formation history, and its
age. Here we present a population synthesis study of the white dwarf population
within 40~pc from the Sun, and compare the results of this study with the
properties of the observed sample. We use a state-of-the-art population
synthesis code based on Monte Carlo techniques, that incorporates the most
recent and reliable white dwarf cooling sequences, an accurate description of
the Galactic neighborhood, and a realistic treatment of all the known
observational biases and selection procedures. We find a good agreement between
our theoretical models and the observed data. In particular, our simulations
reproduce a previously unexplained feature of the bright branch of the white
dwarf luminosity function, which we argue is due to a recent episode of star
formation. We also derive the age of the Solar neighborhood employing the
position of the observed cut-off of the white dwarf luminosity function,
obtaining ~8.9+-0.2 Gyr. We conclude that a detailed description of the
ensemble properties of the population of white dwarfs within 40pc of the Sun
allows us to obtain interesting constraints on the history of the Solar
neighborhood.Comment: 8 pages, 7 figures, accepted for publication in A&
The Ellis semigroup of a nonautonomous discrete dynamical system
We introduce the {\it Ellis semigroup} of a nonautonomous discrete dynamical
system when is a metric compact space. The underlying
set of this semigroup is the pointwise closure of \{f\sp{n}_1 \, |\, n\in
\mathbb{N}\} in the space X\sp{X}.
By using the convergence of a sequence of points with respect to an
ultrafilter it is possible to give a precise description of the semigroup and
its operation. This notion extends the classical Ellis semigroup of a discrete
dynamical system. We show several properties that connect this semigroup and
the topological properties of the nonautonomous discrete dynamical system
Symmetry limit properties of a priori mixing amplitudes for non-leptonic and weak radiative decays of hyperons
We show that the so-called parity-conserving amplitudes predicted in the a
priori mixing scheme for non-leptonic and weak radiative decays of hyperons
vanish in the strong-flavor symmetry limit
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