1,584 research outputs found
The Mixing Angle Revisited
The value of the mixing angle is phenomenologically
deduced from a rather exhaustive and up-to-date analysis of data including
strong decays of tensor and higher-spin mesons, electromagnetic decays of
vector and pseudoscalar mesons, decays into a vector and a
pseudoscalar meson, and other transitions. A value of between
and is consistent with all the present experimental
evidence and the average seems to be
favoured.Comment: 17 pages, LaTeX. 2 references added, some comments on Chiral
Perturbation Theor
Mixing of eta-eta' Mesons in J/psi Decays into a Vector and a Pseudoscalar Meson
The octet-singlet mixing angle in the pseudoscalar meson nonet is
deduced from the rich set of accurate data on decays into a vector and
a pseudoscalar meson. Corrections due to non-ideal - mixing have
been included for the first time and turn out to be crucial to find degrees, which is appreciably less negative than previous
results coming from similar analyses.Comment: 9 pages, LaTeX, full postscript file available via anonymous ftp at
ftp://ftp.ifae.es/preprint/ft/uabft412.p
Aprendizaje significativo del concepto de gen entre estudiantes de biologÃa. OPEL-IPC Venezuela
El gen es un conocimiento biológico abstracto y fundamental que se presenta como entidades fÃsicas con funciones especÃficas y como conocimiento exacto y ahistórico Su tratamiento estructuralista y funcionalista es un obstáculo epistemológico (Bachelard, 1971; El-Hanny, 2005). La intervención didáctica pretendió propiciar un aprendizaje significativo crÃtico (Moreira,2005). Investigación interpretativa micro-etnográfica con 50 sujetos. Interpreta significados que se construyen en: BiologÃa Celular y Genética General, La Intervención analiza lo que acontece en el aula (Ausubel, 2002). Los resultados corresponden con trabajos previos (Stotz, et al, 2004). Existen diferencias significativas a su favor, con espacios para analizar significados, su historia y epistemologÃa
Aprendizaje significativo del concepto de gen entre estudiantes de biologÃa. OPEL-IPC Venezuela
El gen es un conocimiento biológico abstracto y fundamental que se presenta como entidades fÃsicas con funciones especÃficas y como conocimiento exacto y ahistórico Su tratamiento estructuralista y funcionalista es un obstáculo epistemológico (Bachelard, 1971; El-Hanny, 2005). La intervención didáctica pretendió propiciar un aprendizaje significativo crÃtico (Moreira,2005). Investigación interpretativa micro-etnográfica con 50 sujetos. Interpreta significados que se construyen en: BiologÃa Celular y Genética General, La Intervención analiza lo que acontece en el aula (Ausubel, 2002). Los resultados corresponden con trabajos previos (Stotz, et al, 2004). Existen diferencias significativas a su favor, con espacios para analizar significados, su historia y epistemologÃa
Effects of the electrostatic environment on superlattice Majorana nanowires
Finding ways of creating, measuring, and manipulating Majorana bound states (MBSs) in superconducting-semiconducting nanowires is a highly pursued goal in condensed matter physics. It was recently proposed that a periodic covering of the semiconducting nanowire with superconductor fingers would allow both gating and tuning the system into a topological phase while leaving room for a local detection of the MBS wave function. We perform a detailed, self-consistent numerical study of a three-dimensional (3D) model for a finite-length nanowire with a superconductor superlattice including the effect of the surrounding electrostatic environment, and taking into account the surface charge created at the semiconductor surface. We consider different experimental scenarios where the superlattice is on top or at the bottom of the nanowire with respect to a back gate. The analysis of the 3D electrostatic profile, the charge density, the low-energy spectrum, and the formation of MBSs reveals a rich phenomenology that depends on the nanowire parameters as well as on the superlattice dimensions and the external back-gate potential. The 3D environment turns out to be essential to correctly capture and understand the phase diagram of the system and the parameter regions where topological superconductivity is establishedWe thank E. J. H. Lee, H. Beidenkopf, E. G. Michel, N. Avraham, H. Shtrikman, and J. NygÃ¥rd for valuable discussions. Research supported by the Spanish MINECO through Grants No. FIS2016-80434-P, No. BES-2017-080374, and No. FIS2017-84860-R (AEI/FEDER, EU), the European Union's Horizon 2020 research and innovation programme under the FETOPEN Grant Agreement No. 828948 and Grant Agreement LEGOTOP No. 788715, the Ramón y Cajal programme RYC-2011-09345, the MarÃa de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), the DFG (CRC/Transregio 183, EI 519/7- 1), the Israel Science Foundation (ISF), and the Binational Science Foundation (BSF
Kpi form factors and final state interactions in D+ --> K- pi+ pi+ decays
We present a model for the decay D+ --> K- pi+ pi+. The weak interaction part
of this reaction is described using the effective weak Hamiltonian in the
factorisation approach. Hadronic final state interactions are taken into
account through the Kpi scalar and vector form factors fulfilling analyticity,
unitarity and chiral symmetry constraints. The model has only two free
parameters that are fixed from experimental branching ratios. We show that the
modulus and phase of the S wave thus obtained agree nicely with experiment up
to 1.55 GeV. We perform Monte Carlo simulations to compare the predicted Dalitz
plot with experimental analyses. Allowing for a global phase difference between
the S and P waves of -65 degrees, the Dalitz plot of the D+ --> K- pi+ pi+
decay, the Kpi invariant mass spectra and the total branching ratio due to
S-wave interactions are well reproduced.Comment: 24 pages, 4 figures, REVTeX style. A discussion on the isospin 2
component has been included. Two references added. Published in Phys. Rev.
Boron abundance and solar neutrino spectrum distortion
The presence of neutrinos from Boron decay in the flux observed on Earth is
attested by the observation of their energy spectrum. Possible distortions of
the spectrum investigated in current detectors are often interpreted in terms
of evidence in favour or against various schemes of neutrino oscillations. We
stress here that a distortion of the spectrum at high energies could also
result from an increase in the ratio of neutrinos originating from (He+p)
and B reactions. While a B neutrino depletion would contribute to this
effect, an increase in the Hep contribution seems also needed to reproduce the
preliminary data.Comment: 8 pages, 2 figures; abstract and introduction rewritten to match the
conclusions bette
Insights on neutrino lensing
We discuss the gravitational lensing of neutrinos by astrophysical objects.
Unlike photons, neutrinos can cross a stellar core; as a result, the lens
quality improves. We also estimate the depletion of the neutrino flux after
crossing a massive object and the signal amplification expected. While Uranians
alone would benefit from this effect in the Sun, similar effects could be
considered for binary systems.Comment: 15 pages, 4 figures, to be published in Phys. Lett.
Interaction-induced zero-energy pinning and quantum dot formation in Majorana nanowires
Majorana modes emerge in non-trivial topological phases at the edges of specific materials such as proximitized semiconducting nanowires under an external magnetic field. Ideally, they are non-local states that are charge-neutral superpositions of electrons and holes. However, in nanowires of realistic length their wave functions overlap and acquire a finite charge that makes them susceptible to interactions, specifically with the image charges that arise in the electrostatic environment. Considering a realistic threedimensional model of the dielectric surroundings, here we show that, under certain circumstances, these interactions lead to a suppression of the Majorana oscillations predicted by simpler theoretical models, and to the formation of low-energy quantum-dot states that interact with the Majorana modes. Both features are observed in recent experiments on the detection of Majoranas and could thus help to properly characterize themResearch supported by the Spanish Ministry of Economy and Competitiveness through Grants FIS2014-55486-P, FIS2016-80434-P (AEI/FEDER, EU), the Ramón y Cajal programme Grants RYC-2011-09345 and the MarÃa de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377
Improved effective equation for the Rashba spin-orbit coupling in semiconductor nanowires
Semiconductor Rashba nanowires are quasi-one dimensional systems that have
large spin-orbit (SO) coupling arising from a broken inversion symmetry due to
an external electric field. There exist parametrized multiband models that can
describe accurately this effect. However, simplified single band models are
highly desirable to study geometries of recent experimental interest, since
they may allow to incorporate the effects of the low dimensionality and the
nanowire electrostatic environment at a reduced computational cost. Commonly
used conduction band approximations, valid for bulk materials, greatly
underestimate the SO coupling in Zinc-blende crystal structures and
overestimate it for Wurtzite ones when applied to finite cross-section wires,
where confinement effects turn out to play an important role. We demonstrate
here that an effective equation for the linear Rashba SO coupling of the
semiconductor conduction band can reproduce the behavior of more sophisticated
eight-band kp model calculations. This is achieved by adjusting a single
effective parameter that depends on the nanowire crystal structure and its
chemical composition. We further compare our results to the Rashba coupling
extracted from magnetoconductance measurements in several experiments on InAs
and InSb nanowires, finding excellent agreement. This approach may be relevant
in systems where Rashba coupling is known to play a major role, such as in
spintronic devices or Majorana nanowires.Comment: 26 pages, 9 figures. v3: final version with new figures and new
discussion of confinement effect
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