382 research outputs found
Floquet theory of neutrino oscillations in the earth
We review the Floquet theory of linear differential equations with periodic
coefficients and discuss its applications to neutrino oscillations in matter of
periodically varying density. In particular, we consider parametric resonance
in neutrino oscillations which can occur in such media, and discuss
implications for oscillations of neutrinos traversing the earth and passing
through the earth's core.Comment: LaTeX, 28 pages, 8 eps figures. Contribution to the special issue of
Yad. Fiz. dedicated to the memory of A.B. Migda
Comment on the Surface Exponential for Tensor Fields
Starting from essentially commutative exponential map for generic
tensor-valued 2-forms , introduced in \cite{Akh} as direct generalization of
the ordinary non-commutative -exponent for 1-forms with values in matrices
(i.e. in tensors of rank 2), we suggest a non-trivial but multi-parametric
exponential , which can serve as an interesting
multi-directional evolution operator in the case of higher ranks. To emphasize
the most important aspects of the story, construction is restricted to
backgrounds , associated with the structure constants of {\it
commutative} associative algebras, what makes it unsensitive to topology of the
2d surface. Boundary effects are also eliminated (straightfoward generalization
is needed to incorporate them).Comment: 6 page
Exotic smooth structures on 4-manifolds with zero signature
For every integer , we construct infinite families of mutually
nondiffeomorphic irreducible smooth structures on the topological -manifolds
and (2k-1)(\CP#\CPb), the connected sums of
copies of and \CP#\CPb.Comment: 6 page
Comments on QED with background electric fields
It is well known that there is a total cancellation of the
\emph{factorizable} IR divergences in unitary interacting field theories, such
as QED and quantum gravity. In this note we show that such a cancellation does
not happen in QED with background electric fields which can produce pairs.
There is no factorization of the IR divergences.Comment: 14 pages, 1 figur
Resonant neutrino spin-flavor precession and supernova shock revival
A new mechanism of supernova shock revival is proposed, which involves
resonant spin--flavor precession of neutrinos with a transition magnetic moment
in the magnetic field of the supernova. The mechanism can be operative in
supernovae for transition magnetic moments as small as provided
the neutrino mass squared difference is in the range . It is shown that this mechanism can increase the
neutrino--induced shock reheating energy by about 60\%.Comment: 16 pages, latex, 2 figures. added few reference
Supernova prompt neutronization neutrinos and neutrino magnetic moments
It is shown that the combined action of spin-flavor conversions of supernova
neutrinos due to the interactions of their Majorana-type transition magnetic
moments with the supernova magnetic fields and flavor conversions due to the
mass mixing can lead to the transformation of \nu_e born in the neutronization
process into their antiparticles \bar{\nu}_e. Such an effect would have a clear
experimental signature and its observation would be a smoking gun evidence for
the neutrino transition magnetic moments. It would also signify the leptonic
mixing parameter |U_{e3}| in excess of 10^{-2}.Comment: LaTex, 25 pages, 3 figures. v4: Discussion section expanded,
references added. Matches the published versio
Surface superconducting states in yttrium hexaboride single crystal in a tilted magnetic field
We present the results of an experimental study of the nucleation of
superconductivity at the surface of a single crystal YB in a tilted dc
magnetic field. A recently developed experimental technique allowed us to
determine at each side of the sample as a function of the angle
between the dc magnetic field and the surface. Experiment shows that the ratio
in the direction perpendicular to the surface dc
field while according to the theory this ratio should be equal to 1. This sharp
distinction cannot be ascribed to the surface roughness.Comment: 6 pages, 8 figure
On the Perturbative Stability of Quantum Field Theories in de Sitter Space
We use a field theoretic generalization of the Wigner-Weisskopf method to
study the stability of the Bunch-Davies vacuum state for a massless,
conformally coupled interacting test field in de Sitter space. We find that in
theory the vacuum does {\em not} decay, while in
non-conformally invariant models, the vacuum decays as a consequence of a
vacuum wave function renormalization that depends \emph{singularly} on
(conformal) time and is proportional to the spatial volume. In a particular
regularization scheme the vacuum wave function renormalization is the same as
in Minkowski spacetime, but in terms of the \emph{physical volume}, which leads
to an interpretation of the decay. A simple example of the impact of vacuum
decay upon a non-gaussian correlation is discussed. Single particle excitations
also decay into two particle states, leading to particle production that
hastens the exiting of modes from the de Sitter horizon resulting in the
production of \emph{entangled superhorizon pairs} with a population consistent
with unitary evolution. We find a non-perturbative, self-consistent "screening"
mechanism that shuts off vacuum decay asymptotically, leading to a stationary
vacuum state in a manner not unlike the approach to a fixed point in the space
of states.Comment: 36 pages, 4 figures. Version to appear in JHEP, more explanation
Study of the properties of Plessey's electrocardiographic capacitive electrodes for portable systems
Cardiac diseases are still most widely spread in all regions of the world. And more and more devices are invented to satisfy increasing requirements of the patients. One of the perspective technologies in cardiac diagnostics is capacitive sensing ECG electrodes
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