67,810 research outputs found
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&
Holographic Description of Finite Size Effects in Strongly Coupled Superconductors
Despite its fundamental and practical interest, the understanding of
mesoscopic effects in strongly coupled superconductors is still limited. Here
we address this problem by studying holographic superconductivity in a disk and
a strip of typical size . For , where depends on
the chemical potential and temperature, we have found that the order parameter
vanishes. The superconductor-metal transition at is controlled
by mean-field critical exponents which suggests that quantum and thermal
fluctuations induced by finite size effects are suppressed in holographic
superconductors. Intriguingly, the effective interactions that bind the order
parameter increases as decreases. Most of these results are consistent
with experimental observations in Pb nanograins at low temperature and
qualitatively different from the ones expected in a weakly coupled
superconductor.Comment: 4 pages, 3 figure
Disentangling the nuclear shape coexistence in even-even Hg isotopes using the interacting boson model
We intend to provide a consistent description of the even-even Hg isotopes,
172-200Hg, using the interacting boson model including configuration mixing. We
pay special attention to the description of the shape of the nuclei and to its
connection with the shape coexistence phenomenon.Comment: To appear in CGS15 conference proceedings (EPJ Web of Conferences
Electroproduction ratios of Baryon-Meson states and Strangeness Suppression
We describe the electroproduction ratios of baryon-meson states from nucleon,
inferring from the sea quarks in the nucleon using an extension of the quark
model that takes into account the sea. As a result we provide, with no
adjustable parameters, the predictions of ratios of exclusive meson-baryon
final states:, , , , and .
These predictions are in agreement with the new Jlab experimental data showing
that sea quarks play an important role in the electroproduction. We also
predicted further ratios of exclusive reactions that can be measured and tested
in future experiments. In particular, we suggested new experiments on deuterium
and tritium. Such measurements can provide crucial test of different
predictions concerning the structure of nucleon and its sea quarks helping to
solve an outstanding problem. Finally, we computed the so called strangeness
suppression factor, , that is the suppression of strange
quark-antiquarks compared to nonstrange pairs, and we found that our finding
with this simple extension of the quark model is in good agreement with the
results of Jlab and CERN experiments.Comment: 4 pages, 1figur
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