724 research outputs found
Neutrino Quantum Kinetics
We present a formulation of the quantum kinetic equations (QKEs) which govern
the evolution of neutrino flavor at high density and temperature. Here, the
QKEs are derived from the ground up, using fundamental neutrino interactions
and quantum field theory. We show that the resulting QKEs describe coherent
flavor evolution with an effective mass when inelastic scattering is
negligible. The QKEs also contain a collision term. This term can reduce to the
collision term in the Boltzmann equation when scattering is dominant and the
neutrino effective masses and density matrices become diagonal in the
interaction basis. We also find that the QKE's include equations of motion for
a new dynamical quantity related to neutrino spin. This quantity decouples from
the equations of motion for the density matrices at low densities or in
isotropic conditions. However, the spin equations of motion allow for the
possibility of coherent transformation between neutrinos and antineutrinos at
high densities and in the presence of anisotropy. Although the requisite
conditions for this exist in the core collapse supernova and compact object
merger environments, it is likely that only a self consistent incorporation of
the QKEs in a sufficiently realistic model could establish whether or not
significant neutrino-antineutrino conversion occurs.Comment: Revised version, published in Physical Review
Spin dependent recombination based magnetic resonance spectroscopy of bismuth donor spins in silicon at low magnetic fields
Low-field (6-110 mT) magnetic resonance of bismuth (Bi) donors in silicon has
been observed by monitoring the change in photoconductivity induced by spin
dependent recombination. The spectra at various resonance frequencies show
signal intensity distributions drastically different from that observed in
conventional electron paramagnetic resonance, attributed to different
recombination rates for the forty possible combinations of spin states of a
pair of a Bi donor and a paramagnetic recombination center. An excellent
tunability of Bi excitation energy for the future coupling with superconducting
flux qubits at low fields has been demonstrated.Comment: 5 pages, 4 figure
A New Spin on Neutrino Quantum Kinetics
Recent studies have demonstrated that in anisotropic environments a coherent
spin-flip term arises in the Quantum Kinetic Equations (QKEs) which govern the
evolution of neutrino flavor and spin in hot and dense media. This term can
mediate neutrino-antineutrino transformation for Majorana neutrinos and
active-sterile transformation for Dirac neutrinos. We discuss the physical
origin of the coherent spin-flip term and provide explicit expressions for the
QKEs in a two-flavor model with spherical geometry. In this context, we
demonstrate that coherent neutrino spin transformation depends on the absolute
neutrino mass and Majorana phases.Comment: 11 pages, 3 figures, Major changes compared to v1, accepted for
publication in Physics Letters
Multimedia technology in teaching mathematics pupils 1 – 4 classes
We describe the use of multimedia technology in teaching mathematics in elementary school. The synthesis, systematization, synthesis of existing theoretical positions that make it possible to organize teaching mathematics elementary school students using multimedia technology. Used systematic and comparative analysis of scientific-methodological and psycho-pedagogical literature. The concept multimedia support teaching mathematics in elementary school. Developed requirements and proposed guidelines for creating and using multimedia learning support during lessons in mathematics 1 – 4 classes: presentations, simulators, dynamic models, educational expert systems. Proved that the use of the investigated technologies grounded in multimedia teaching mathematics accompanied by elementary school students during development is important to ensure the selection of appropriate methods of components that should create new opportunities prepare students while changing living conditions, encourage self-education.Keywords: teaching mathematics, primary school, multimedia technology, multimedia support training requirements.Описано використання мультимедійних технологій у навчанні математики в початковій школі. Здійснено синтез, систематизацію, узагальнення наявних теоретичних положень, що вможливлюють організацію навчання математики учнів початкової школи з використанням мультимедійних технологій. Використано системний і порівняльний аналіз науково-методичної та психолого-педагогічної літератури. Уточнено поняття мультимедійного супроводу навчання математики в початковій школі. Розроблено вимоги та запропоновано методичні рекомендації щодо створення та використання мультимедійного супроводу навчання під час уроків математики у 1 – 4 класах. Показано, що використання досліджуваних технологій ґрунтоване на мультимедійному супроводі навчання математики учнів початкової школи, під час розроблення якого важливо забезпечувати вибір відповідних компонентів методики, що має створювати можливості нової підготовки учнів під час зміни умов життєдіяльності, стимулювати самоосвіту.Ключові слова: навчання математики, початкова школа, мультимедійні технології, мультимедійний супровід навчання, вимоги
Coherent storage of photoexcited triplet states using 29Si nuclear spins in silicon
Pulsed electron paramagnetic resonance spectroscopy of the photoexcited,
metastable triplet state of the oxygen-vacancy center in silicon reveals that
the lifetime of the ms = \pm1 sub-levels differ significantly from that of the
ms =0 state. We exploit this significant difference in decay rates to the
ground singlet state to achieve nearly ~100% electron spin polarization within
the triplet. We further demonstrate the transfer of a coherent state of the
triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor 29Si
nuclear spin. We measure the coherence time of the 29 Si nuclear spin employed
in this operation and find it to be unaffected by the presence of the triplet
electron spin and equal to the bulk value measured by nuclear magnetic
resonance.Comment: 5 pages, 4 figure
Neutrino energy transport in weak decoupling and big bang nucleosynthesis
We calculate the evolution of the early universe through the epochs of weak
decoupling, weak freeze-out and big bang nucleosynthesis (BBN) by
simultaneously coupling a full strong, electromagnetic, and weak nuclear
reaction network with a multi-energy group Boltzmann neutrino energy transport
scheme. The modular structure of our code provides the ability to dissect the
relative contributions of each process responsible for evolving the dynamics of
the early universe in the absence of neutrino flavor oscillations. Such an
approach allows a detailed accounting of the evolution of the ,
, , , , energy
distribution functions alongside and self-consistently with the nuclear
reactions and entropy/heat generation and flow between the neutrino and
photon/electron/positron/baryon plasma components. This calculation reveals
nonlinear feedback in the time evolution of neutrino distribution functions and
plasma thermodynamic conditions (e.g., electron-positron pair densities), with
implications for: the phasing between scale factor and plasma temperature; the
neutron-to-proton ratio; light-element abundance histories; and the
cosmological parameter \neff. We find that our approach of following the time
development of neutrino spectral distortions and concomitant entropy production
and extraction from the plasma results in changes in the computed value of the
BBN deuterium yield. For example, for particular implementations of quantum
corrections in plasma thermodynamics, our calculations show a increase
in deuterium. These changes are potentially significant in the context of
anticipated improvements in observational and nuclear physics uncertainties.Comment: 37 pages, 12 Figures, 6 Table
Neutrino scattering and flavor transformation in supernovae
We argue that the small fraction of neutrinos that undergo direction-changing
scattering outside of the neutrinosphere could have significant influence on
neutrino flavor transformation in core-collapse supernova environments. We show
that the standard treatment for collective neutrino flavor transformation is
adequate at late times, but could be inadequate in the crucial shock
revival/explosion epoch of core-collapse supernovae, where the potentials that
govern neutrino flavor evolution are affected by the scattered neutrinos.
Taking account of this effect, and the way it couples to entropy and
composition, will require a new paradigm in supernova modeling.Comment: 5 pages, 3 figure
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