21,119 research outputs found
The action of neutrino ponderomotive force on supernova dynamics
Collective interactions of a beam of neutrinos/antineutrinos traversing a
dense magnetized plasma of electrons/positrons, protons and neutrons are
studied with particular reference to the case of a Supernova. We find that the
ponderomotive force exerted by neutrinos gives, contrary to expectations, a
negligible contribution to the revival of the shock for a successful Supernova
explosion, although new types of convection and plasma cooling processes
induced by the ponderomotive force could be, in principle, relevant for the
dynamics itself.Comment: latex, 14 pages; numerical error corrected, conclusions changed; to
be published in Mod. Phys. Lett.
Majorana and the path-integral approach to Quantum Mechanics
We give, for the first time, the English translation of a manuscript by
Ettore Majorana, which probably corresponds to the text for a seminar delivered
at the University of Naples in 1938, where he lectured on Theoretical Physics.
Some passages reveal a physical interpretation of the Quantum Mechanics which
anticipates of several years the Feynman approach in terms of path integrals,
independently of the underlying mathematical formulation.Comment: revtex, 9 pages, 2 figures; a contribution in the centenary of the
birth of Ettore Majoran
Physical realization of Photonic Klein Tunneling
General physical conditions for the occurrence of photonic Klein tunneling
are studied, where (controlled) spontaneous emission from the devices
considered plays a key role. The specific example of a simple dielectric slab
bounded by two dielectric half spaces with arbitrary refractive indices is
worked out quite in detail, the measured reflection and transmission
probabilities being calculated analytically. It is found that, in given cases,
the measured reflection probability may be arbitrarily large (for large
incident wavelengths) irrespective of the fact that the transmission
probability is exponentially suppressed or not. Other interesting features of
photonic Klein tunneling driven by (controlled) spontaneous emission are as
well envisaged for practical applications.Comment: revtex4, 6 pages, 4 figure
A Personal Point of View about Scientific Discussions on Free Will
I briefly present a personal view about alleged scientific results on free
will.Comment: latex, 3 pages, no figure
Four variations on Theoretical Physics by Ettore Majorana
An account is given of some topical unpublished work by Ettore Majorana,
revealing his very deep intuitions and skilfulness in Theoretical Physics. The
relevance of the quite unknown results obtained by him is pointed out as well.Comment: latex, 23 pages, 1 figure; review article to be published in the
special issue of EJTP dedicated to the centenary of the birth of Ettore
Majoran
Transition from Majorana to Weyl fermions and anapole moments
The apparent splitting of zero-bias conductance peaks, apparently observed in
recent experiments concerning Majorana fermions in nanowires coupled to
superconductors, can be interpreted as a manifestation of a transition in the
structure from (massive) Majorana to (massless) Weyl fermions. A modification
of the experiments in order to test such phenomenon is proposed by making
recourse to the only possible electromagnetic interaction allowed to (massive)
Majorana particles and mediated by their anapole moment. In suitably designed
heterostructures with toroidal symmetry, the additional anapole interaction
manifests itself in the lowering of the critical magnetic field required for
the appearance of the zero-bias peak, a shift that can be directly measured and
thus reveal the presence of Majorana (rather than Weyl) fermions. Anapole
interactions, though not previously considered, may also be a powerful method
to control the dynamics of Majorana fermions, and then to manipulate the qubit
state in quantum computationComment: revtex, 6 pages, 2 figures; to be published in Europhysics Letter
A demonstration device for cosmic rays telescopes
We describe a hands-on accurate demonstrator for cosmic rays realized by six
high school students, whose main aim is to show the relevance and the
functioning of the principal parts of a cosmic rays telescope (muon detector),
with the help of two large size wooden artifacts. The first one points out how
cosmic rays can be tracked in a muon telescope, while the other one shows the
key avalanche process of electronic ionization that effectively allows muon
detection through a photomultiplier. Incoming cosmic rays are visualized in
terms of laser beams, whose 3D trajectory is highlighted by the turning on of
LEDs on two orthogonal matrices. Instead the avalanche ionization process is
demonstrated through the avalanche falling of glass marbles on an inclined
plane, finally turning on a LED. A pictured poster accompanying the
demonstrator is as well effective in assisting cosmic rays demonstration and
its detection. The success of the demonstrator has been fully proven by general
public during a Science Festival, the corresponding project winning the
Honorable Mention in a dedicated competition.Comment: Latex, 8 pages, 6 figures; to be published in Physics Educatio
Hole theory and Quantum Electrodynamics in an unknown French manuscript by Ettore Majorana
We give an accurate historical and scientific account of a previously unknown
manuscript written by Ettore Majorana in French. The retrieved text deals with
Quantum Electrodynamics by using the formalism of field quantization, and it is
here reported, for the first time, in translation. It is likely related to an
invited talk for a conference at Leningrad (or Kharkov) in 1933 (or 1934)
which, however, Majorana never attended. Probably this manuscript refers to the
last missing papers of the ``Senatore folder'', given by Majorana to one
student of his at the University of Naples in 1938, just before his
disappearance.Comment: 16 pages, latex, amsar
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