308 research outputs found
Transition Radiation by Standard Model Neutrinos at an Interface
We discuss the transition radiation process at an
interface of two media. The medium fulfills the dual purpose of inducing an
effective neutrino-photon vertex and of modifying the photon dispersion
relation. The transition radiation occurs when at least one of those quantities
have different values in different media. We present a result for the
probability of the transition radiation which is both accurate and analytic.
For MeV neutrino crossing polyethylene-vacuum interface the
transition radiation probability is about and the energy intensity
(deposition) is about eV. At the surface of the neutron stars the
transition radiation probability may be . Our result on three
orders of magnitude is larger than the results of previous calculations.}Comment: invited talk, to appear in the proceedings of the XLVIth Rencontres
de Moriond EW 201
Degenerate Neutrinos and CP Violation
We have studied mixing and masses of three left handed Majorana neutrinos in
the model, which assumes exactly degenerate neutrino masses at some "neutrino
unification" scale. Such a simple theoretical ansatz naturally leads to
quasidegenerate neutrinos. The neutrino mass splittings induced by
renormalization effects. In the model we found that the parameters of the
neutrino physics (neutrino mass spectrum, mixing angles and CP violation
phases) are strongly intercorrelated to each other. From these correlations we
got strong bounds on the parameters which could be checked in the oscillation
experiments.Comment: 5 pages, latex, presented at CAPP200
Describing neutrino oscillations in matter with Magnus expansion
We present new formalism for description of the neutrino oscillations in
matter with varying density. The formalism is based on the Magnus expansion and
has a virtue that the unitarity of the S-matrix is maintained in each order of
perturbation theory. We show that the Magnus expansion provides better
convergence of series: the restoration of unitarity leads to smaller deviations
from the exact results especially in the regions of large transition
probabilities. Various expansions are obtained depending on a basis of neutrino
states and a way one splits the Hamiltonian into the self-commuting and
non-commuting parts. In particular, we develop the Magnus expansion for the
adiabatic perturbation theory which gives the best approximation. We apply the
formalism to the neutrino oscillations in matter of the Earth and show that for
the solar oscillation parameters the second order Magnus adiabatic expansion
has better than 1% accuracy for all energies and trajectories. For the
atmospheric and small 1-3 mixing the approximation works well ( accuracy for ) outside the resonance region
(2.7 - 8) GeV.Comment: Discussions expanded, two figures and references added, the version
will appear in Nucl. Phys.
Attenuation effect and neutrino oscillation tomography
Attenuation effect is the effect of weakening of contributions to the
oscillation signal from remote structures of matter density profile. The effect
is a consequence of integration over the neutrino energy within the energy
resolution interval. Structures of a density profile situated at distances
larger than the attenuation length, , are not "seen". We show
that the origins of attenuation are (i) averaging of oscillations in certain
layer(s) of matter, (ii) smallness of matter effect: , where is the matter potential, and (iii) specific
initial and final states on neutrinos. We elaborate on the graphic description
of the attenuation which allows us to compute explicitly the effects in the
order for various density profiles and oscillation channels. The
attenuation in the case of partial averaging is described. The effect is
crucial for interpretation of oscillation data and for the oscillation
tomography of the Earth with low energy (solar, supernova, atmospheric, {\it
etc.}) neutrinos.Comment: 24 pages, 8 figures, typos corrected, more explanations adde
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