5,751 research outputs found
Majorana vs Pseudo-Dirac Neutrinos at the ILC
Neutrino masses could originate in seesaw models testable at colliders, with
light mediators and an approximate lepton number symmetry. The minimal model of
this type contains two quasi-degenerate Majorana fermions forming a
pseudo-Dirac pair. An important question is to what extent future colliders
will have sensitivity to the splitting between the Majorana components, since
this quantity signals the breaking of lepton number and is connected to the
light neutrino masses. We consider the production of these neutral heavy
leptons at the ILC, where their displaced decays provide a golden signal: a
forward-backward charge asymmetry, which depends crucially on the mass
splitting between the two Majorana components. We show that this observable can
constrain the mass splitting to values much lower than current bounds from
neutrinoless double beta decay and natural loop corrections.Comment: 16 pages, 5 figures; v2: Minor changes, version accepted for
publication in EPJ
On the index theorem for Wilson fermions
We consider a Wilson-Dirac operator with improved chiral properties. We show
that, for arbitrarily rough gauge fields, it satisfies the index theorem if we
identify the zero modes with the small real eigenvalues of the fermion operator
and use the geometrical definition of topological charge. This is also
confirmed in a numerical study of the quenched Schwinger model. These results
suggest that integer definitions of the topological charge based on counting
real modes of the Wilson operator are equivalent to the geometrical definition.
The problem of exceptional configurations and the sign problem in simulations
with an odd number of dynamical Wilson fermions are briefly discussed.Comment: Latex, 18 pages, 6 figure
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Constructing immigrants in UK legislation and Administration informative texts: A corpus-driven study (2007–2011)
Research has shown that immigrants tend to be negatively constructed in the discourse of the media. In the context of the European Union (EU), British newspapers reportedly offer largely negative or partial constructions of these individuals. These representations contribute to jeopardizing the integration of this group of people, as their social construction reflects and influences the attitudes of EU citizens and the immigration policies. Our research examines the collocational profile of the lemma ‘migrant’ in the UK legislation and UK Administration informative texts from 2007 to 2011. While our results show that the UK Administration avoids an explicit negative construction of immigrants coming to the United Kingdom, we have found that they are partially constructed as a homogeneous, well-categorized group through an extremely limited set of lexical items that tend to prime their adscription to tiers. We argue that the representation of immigrants in the legislation points to the fact that UK laws and official information during the period 2007–2011 were more focused on legitimating the control over this group of individuals than on creating the conditions for better integration policies.Spanish Ministry of Economy and Competitiveness (Grant FFI2011-30214: Lenguaje de la Administración Pública en el ámbito de la extranjería: estudio multilingüe e implicaciones culturales)This is the author accepted manuscript. The final version is available from SAGE Publications via http://dx.doi.org/10.1177/095792651667670
Open ocean temperature and salinity trends in the Canary Current Large Marine Ecosystem
The Sea Surface Temperature in the Canary Current Large Marine Ecosystem (CCLME) for the 32 years in
the period 1982‐2013 shows a mean warming trend of 0.28°C decade‐1. However, this overall warming
trend shows significant changes due to the influence of the different dynamical regimes that coexist in the
CCLME. Near the coast, in the area under the influence of the upwelling, between Cape Blanc and Cape
Beddouza, the warming trend is not statistically different from zero. Near the coast, but in the waters
under the influence of downwelling, between Cape Verde and Cape Blanc, the warming trend is higher
(>0.5°C decade‐1), and statistically significant. In the oceanic regions, there is a statistically significant trend
of 0.25°C decade‐1, a trend that is also observed in waters shallower than the permanent thermocline (200‐
600 dbar). This warming rate is density compensate, with an increase in salinity of 0.02 decade‐1. Neither
the intermediate waters nor the upper deep waters show any statistically significant trend. The deep
waters (2600‐3600 dbar) in the oceanic waters north of the Canary Islands, show a warming rate of
‐0.01°C decade‐1 and a freshening of ‐0.002 decade‐1.En prens
Seasonal Growth Curves of Perennial Ryegrass in Mexico
An experiment was established at Colegio de Postgraduados Research Station, Texcoco, México to evaluate the seasonal pattern of growth curve of perennial ryegrass (Lolium perenne) swards. Growth rate increases rapidly from a low level immediately after defoliation, and eventually reaches an equilibrium level as the amount of green leaf in the sward stabilize. The time required to reach this state varied according to the season of year, with the four seasons ranked in the order: spring (4 weeks) \u3c summer (5 weeks) \u3c autumn and winter (6 weeks). Once swards reached equilibrium, growth rates started to decline as a consequence of an increase in dead material and pseudostem. These increases were highest in spring and lowest in winter. The results of this study suggest that sward management to maximise herbage production and utilisation in ryegrass swards must be done once the highest green leaf mass is reached. In this trial, it was reached at 5, 6, 6 and 4 weeks in summer, autumn, winter and spring, respectively
The Canary Basin contribution to the seasonal cycle of the Atlantic Meridional Overturning Circulation at 26°N
This study examines the seasonal cycle of the Atlantic Meridional Overturning Circulation (AMOC) and its eastern boundary contributions. The cycle has a magnitude of 6 Sv, as measured by the RAPID/MOCHA/WBTS project array at 26°N, which is driven largely by the eastern boundary. The eastern boundary variations are explored in the context of the regional circulation around the Canary Islands. There is a 3 month lag between maximum wind forcing and the largest eastern boundary transports, which is explained in terms of a model for Rossby wave generated at the eastern boundary. Two dynamic processes take place through the Lanzarote Passage (LP) in fall: the recirculation of the Canary Current and the northward flow of the Intermediate Poleward Undercurrent. In contrast, during the remaining seasons the transport through the LP is southward due to the Canary Upwelling Current. These processes are linked to the seasonal cycle of the AMOC
Above threshold ionization by few-cycle spatially inhomogeneous fields
We present theoretical studies of above threshold ionization (ATI) produced
by spatially inhomogeneous fields. This kind of field appears as a result of
the illumination of plasmonic nanostructures and metal nanoparticles with a
short laser pulse. We use the time-dependent Schr\"odinger equation (TDSE) in
reduced dimensions to understand and characterize the ATI features in these
fields. It is demonstrated that the inhomogeneity of the laser electric field
plays an important role in the ATI process and it produces appreciable
modifications to the energy-resolved photoelectron spectra. In fact, our
numerical simulations reveal that high energy electrons can be generated.
Specifically, using a linear approximation for the spatial dependence of the
enhanced plasmonic field and with a near infrared laser with intensities in the
mid- 10^{14} W/cm^{2} range, we show it is possible to drive electrons with
energies in the near-keV regime. Furthermore, we study how the carrier envelope
phase influences the emission of ATI photoelectrons for few-cycle pulses. Our
quantum mechanical calculations are supported by their classical counterparts
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