7,037 research outputs found
Chiral asymmetry during the EWPT from CP-violating scattering off bubble walls
We compute a net electric current during a first order EWPT arising from the
asymmetric propagation of fermion chiral modes due to a CP-violating
interaction with the Higgs. The interaction is quantified in terms of a
CP-violating phase in the bubble wall that separate both false and true vacuum
phases. We comment on the possibility of this current to generate a seed
magnetic field and its implications for primordial magne- togenesis in the
early Universe.Comment: To appear in the proceedings of the XLVII of the International
Symposium of Multiparticle Dynamics, Tlaxcala, Mexico, September 10-15, 201
Radial velocities and metallicities from infrared Ca II triplet spectroscopy of open clusters II. Berkeley 23, King 1, NGC 559, NGC 6603 and NGC 7245
Context: Open clusters are key to studying the formation and evolution of the
Galactic disc. However, there is a deficiency of radial velocity and chemical
abundance determinations for open clusters in the literature. Aims: We intend
to increase the number of determinations of radial velocities and metallicities
from spectroscopy for open clusters. Methods: We acquired medium-resolution
spectra (R~8000) in the infrared region Ca II triplet lines (~8500 AA) for
several stars in five open clusters with the long-slit IDS spectrograph on the
2.5~m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain).
Radial velocities were obtained by cross-correlation fitting techniques. The
relationships available in the literature between the strength of infrared Ca
II lines and metallicity were also used to derive the metallicity for each
cluster. Results: We obtain = 48.6+/-3.4, -58.4+/-6.8, 26.0+/-4.3 and
-65.3+/-3.2 km s-1 for Berkeley 23, NGC 559, NGC 6603 and NGC 7245,
respectively. We found [Fe/H] =-0.25+/-0.14 and -0.15+/-0.18 for NGC 559 and
NGC 7245, respectively. Berkeley 23 has a low metallicity, [Fe/H]
=-0.42+/-0.13, similar to other open clusters in the outskirts of the Galactic
disc. In contrast, we derived a high metallicity ([Fe/H] =+0.43+/-0.15) for NGC
6603, which places this system among the most metal rich known open clusters.
To our knowledge, this is the first determination of radial velocities and
metallicities from spectroscopy for these clusters, except NGC 6603, for which
radial velocities had been previously determined. We have also analysed ten
stars in the line of sight to King 1. Because of the large dispersion obtained
in both radial velocity and metallicity, we cannot be sure that we have sampled
true cluster members.Comment: 10 pages, 5 figures, accepted for publication in A&A (minor
modifications
BANKING EFFICIENCY AND EUROPEAN INTEGRATION. IMPLICATIONS OF THE BANKING REFORM IN ROMANIA
The aim of this study is to analyze the influence that the European integrationprocess has had over the banking efficiency levels in those countries which have recentlyexperienced more intensely the European integration process. For this purpose we haveanalyzed, using stochastic frontier models (SFA), applied to panel data, bank efficiency levelsof a sample of 240 banks from 12 countries during the period 2000 to 2008. The resultssustain the hypothesis that the European integration process has significantly improved theefficiency levels in these countries. However, the improvements havenât appeared simply bythe accession to the EU, but have appeared during the process. In order to illustrate the results, we have analyzed the banking system in Romania inthe context of the European integration, a country which because of the delay in the initiationof the reforms, despite belonging to the EU, it hasnât still recorded the essential improvementsin banking efficiency associated to this process that the other new members have alreadyexperienced.banking efficiency, European integration, stochastic models, banking reform.
Soft X-ray Absorption by High-Redshift Intergalactic Helium
The Lyman alpha absorption from intergalactic, once-ionized helium (HeII) has
been measured with HST in four quasars over the last few years, over the
redshift range 2.4 < z < 3.2. These observations have indicated that the HeII
reionization may not have been completed until z\simeq 2.8, and that large
fluctuations in the intensity of the HeII-ionizing background were present
before this epoch. The detailed history of HeII reionization at higher
redshifts is, however, model-dependent and difficult to determine from these
observations, because the IGM can be completely optically thick to Lya photons
when only a small fraction of the helium remains as HeII. In addition, finding
quasars in which the HeII Lya absorption can be observed becomes increasingly
difficult at higher redshift, owing to the large abundance of hydrogen Lyman
limit systems.
It is pointed out here that HeII in the IGM should also cause detectable
continuum absorption in the soft X-rays. The spectrum of a high-redshift source
seen behind the IGM when most of the helium was HeII should recover from the
HeII Lyman continuum absorption at an observed energy \sim 0.1 keV. Galactic
absorption will generally be stronger, but not by a large factor; the
intergalactic HeII absorption can be detected as an excess over the expected
Galactic absorption from the 21cm HI column density. In principle, this method
allows a direct determination of the fraction of helium that was singly ionized
as a function of redshift, if the measurement is done on a large sample of
high-redshift sources over a range of redshift.Comment: accepted to The Astrophysical Journal Letter
Hunting for open clusters in \textit{Gaia} DR2: the Galactic anticentre
The Gaia Data Release 2 (DR2) provided an unprecedented volume of precise
astrometric and excellent photometric data. In terms of data mining the Gaia
catalogue, machine learning methods have shown to be a powerful tool, for
instance in the search for unknown stellar structures. Particularly, supervised
and unsupervised learning methods combined together significantly improves the
detection rate of open clusters. We systematically scan Gaia DR2 in a region
covering the Galactic anticentre and the Perseus arm and
, with the goal of finding any open clusters that may
exist in this region, and fine tuning a previously proposed methodology
successfully applied to TGAS data, adapting it to different density regions.
Our methodology uses an unsupervised, density-based, clustering algorithm,
DBSCAN, that identifies overdensities in the five-dimensional astrometric
parameter space that may correspond
to physical clusters. The overdensities are separated into physical clusters
(open clusters) or random statistical clusters using an artificial neural
network to recognise the isochrone pattern that open clusters show in a colour
magnitude diagram. The method is able to recover more than 75% of the open
clusters confirmed in the search area. Moreover, we detected 53 open clusters
unknown previous to Gaia DR2, which represents an increase of more than 22%
with respect to the already catalogued clusters in this region. We find that
the census of nearby open clusters is not complete. Different machine learning
methodologies for a blind search of open clusters are complementary to each
other; no single method is able to detect 100% of the existing groups. Our
methodology has shown to be a reliable tool for the automatic detection of open
clusters, designed to be applied to the full Gaia DR2 catalogue.Comment: 8 pages, accepted by Astronomy and Astrophysics (A&A) the 14th May,
2019. Tables 1 and 2 available at the CD
New axion and hidden photon constraints from a solar data global fit
We present a new statistical analysis that combines helioseismology (sound
speed, surface helium and convective radius) and solar neutrino observations
(the B and Be fluxes) to place upper limits to the properties of non
standard weakly interacting particles. Our analysis includes theoretical and
observational errors, accounts for tensions between input parameters of solar
models and can be easily extended to include other observational constraints.
We present two applications to test the method: the well studied case of axions
and axion-like particles and the more novel case of low mass hidden photons.
For axions we obtain an upper limit at for the axion-photon coupling
constant of . For hidden
photons we obtain the most restrictive upper limit available accross a wide
range of masses for the product of the kinetic mixing and mass of at . Both cases improve the previous solar
constraints based on the Standard Solar Models showing the power of using a
global statistical approach.Comment: 23 pages, 12 figure
Sustainability Assessment of indicators for integrated water resources management
The scientific community strongly recommends the adoption of indicators for the evaluation and monitoring of progress towards sustainable development. Furthermore, international organizations consider that indicators are powerful decision-making tools. Nevertheless, the quality and reliability of the indicators depends on the application of adequate and appropriate criteria to assess them. The general objective of this study was to evaluate how indicators related to water use and management perform against a set of sustainability criteria. Our research identified 170 indicators related to water use and management. These indicators were assessed by an international panel of experts that evaluated whether they fulfil the four sustainability criteria: social, economic, environmental, and institutional. We employed an evaluation matrix that classified all indicators according to the DPSIR (Driving Forces, Pressures, States, Impacts and Responses) framework. A pilot study served to test and approve the research methodology before carrying out the full implementation. The findings of the study show that 24 indicators comply with the majority of the sustainability criteria; 59 indicators are bi-dimensional (meaning that they comply with two sustainability criteria); 86 are one-dimensional indicators (fulfilling just one of the four sustainability criteria) and one indicator do not fulfil any of the sustainability criteria.Postprint (author's final draft
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