Polarization fields in nitride nanostructures: ten points to think about

Macroscopic polarization, both of intrinsic and piezoelectric nature, is unusually strong in III-V nitrides, and the built in electric fields in the layers of nitride-based nanostructures, stemming from polarization changes at heterointerfaces, have a major impact on the properties of single and multiple quantum wells, high mobility transistors, and thin films. The concepts involved in the theory and applications of polarization in nitrides have encountered some resistance in the field. Here we discuss critically ten ``propositions'' aimed at clarifying the main controversial issues.Comment: RevTeX 5 pages, 2 embedded figure

Dynamical neutrino masses in the generalized Chaplygin gas scenario with mass varying CDM

Neutrinos coupled to an underlying scalar field in the scenario for unification of mass varying dark matter and cosmon-{\em like} dark energy is examined. In the presence of a tiny component of mass varying neutrinos, the conditions for the present cosmic acceleration and for the stability issue are reproduced. It is assumed that {\em sterile} neutrinos behave like mass varying dark matter coupled to mass varying {\em active} neutrinos through the {\em seesaw} mechanism, in a kind of {\em mixed} dark matter sector. The crucial point is that the dark matter mass may also exhibit a dynamical behavior driven by the scalar field. The scalar field mediates the nontrivial coupling between the mixed dark matter and the dark energy responsible for the accelerated expansion of the universe. The equation of state of perturbations reproduce the generalized Chaplygin gas (GCG) cosmology so that all the effective results from the GCG paradigm are maintained, being perturbatively modified by neutrinos.Comment: 19 pages, 5 figure

Measurement of the Atmospheric Muon Neutrinos with the MACRO Detector

The flux of muons induced by atmospheric neutrinos has been measured with the MACRO detector. Different event topologies have been detected, due to neutrino interactions in the apparatus and in the rock below it. The upward-throughgoing muon sample is the larger one and is generated by neutrinos with a peak energy of ~100 GeV. The observed upward-throughgoing muons are 26 % fewer than expected and the zenith angle distribution does not fit with the expected one. Assuming \mutau neutrino oscillation, the angular shape and the normalization factor suggest maximal mixing and \Delta m^2 of a few times 10^{-3} eV^2. Also the other event categories induced by low-energy neutrinos (peak energy ~ 4 GeV) show a deficit of observed events. The value of this deficit and its uniformity with respect to the angular bins are in agreement with the oscillation parameters suggested by the analysis of the upward-throughgoing muon sample.Comment: 13 pages, 9 figures, Proceedings of La Thuile Conferenc

Relativistic tunneling and accelerated transmission

We obtain the solutions for the tunneling zone of a one-dimensional electrostatic potential in the relativistic (Dirac to Klein-Gordon) wave equation regime when the incoming wave packet exhibits the possibility of being almost totally transmitted through the potential barrier. The conditions for the occurrence of accelerated and, eventually, superluminal tunneling transmission probabilities are all quantified and the problematic superluminal interpretation originated from the study based on non-relativistic dynamics of tunneling is overcome. The treatment of the problem suggests revealing insights into condensed-matter experiments using electrostatic barriers in single- and bi-layer graphene, for which the accelerated tunneling effect deserves a more careful investigation.Comment: 10 pages, 1 figur

Delay time computation for relativistic tunneling particles

We study the tunneling zone solutions of a one-dimensional electrostatic potential for the relativistic (Dirac to Klein-Gordon) wave equation when the incoming wave packet exhibits the possibility of being almost totally transmitted through the barrier. The transmission probabilities, the phase times and the dwell times for the proposed relativistic dynamics are obtained and the conditions for the occurrence of accelerated tunneling transmission are all quantified. We show that, in some limiting cases, the analytical difficulties that arise when the stationary phase method is employed for obtaining phase (traversal) tunneling times are all overcome. Lessons concerning the phenomenology of the relativistic tunneling suggest revealing insights into condensed-matter experiments using electrostatic barriers for which the accelerated tunneling effect can be observed.Comment: 17 pages, 4 figure