13 research outputs found
Phenomenology of neutrino physics in the Kaluza-Klein theories of low scale gravity
We discuss the phenomenological consequences of theories which describe
sterile neutrinos in large extra dimensions. We show that the Kaluza-Klein
tower of the singlet neutrinos, albeit tiny individual contribution in
electroweak processes, act cumulatively, giving rise to non-universality of the
weak interactions of the light neutrinos and to flavour-violating radiative
processes. Owing to these non-decoupling effects of th Kaluza--Klein neutrinos,
we derive strong constraints on the parameters of the theory that originates
from the non-observation of flavour-violating and universality-breaking
phenomena. In this theory we propose a four-neutrino model which can reconcile
the existing data coming from underground experiments in terms of neutrino
oscillations, together with the hint from the LSND experiment and a possible
neutrino contribution to the hot dark matter of the Universe.Comment: 5 pages, Talk given at the EuroConference on Frontiers in Particle
Astrophysics and Cosmology, San Feliu de Guixols, Spain, 30 September - 5
October, 200
Transition Radiation by Neutrinos
We calculate the transition radiation process at an
interface of two media. The neutrinos are taken to be with only standard-model
couplings. 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. The neutrino mass is ignored due to its
negligible contribution. 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 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
An accurate analytic description of neutrino oscillations in matter
A simple closed-form analytic expression for the probability of two-flavour
neutrino oscillations in a matter with an arbitrary density profile is derived.
Our formula is based on a perturbative expansion and allows an easy calculation
of higher order corrections. The expansion parameter is small when the density
changes relatively slowly along the neutrino path and/or neutrino energy is not
very close to the Mikheyev-Smirnov-Wolfenstein (MSW) resonance energy. Our
approximation is not equivalent to the adiabatic approximation and actually
goes beyond it. We demonstrate the validity of our results using a few model
density profiles, including the PREM density profile of the Earth. It is shown
that by combining the results obtained from the expansions valid below and
above the MSW resonance one can obtain a very good description of neutrino
oscillations in matter in the entire energy range, including the resonance
region.Comment: 16 pages,6 figure
The electromagnetic vertex of neutrinos in an electron background and a magnetic field
We study the electromagnetic vertex function of a neutrino that propagates in
an electron background in the presence of a static magnetic field. The
structure of the vertex function under the stated conditions is determined and
it is written down in terms of a minimal and complete set of tensors. The
one-loop expressions for all the form factors is given, up to terms that are
linear in the magnetic field, and the approximate integral formulas that hold
in the long wavelength limit are obtained. We discuss the physical
interpretation of some of the form factors and their relation with the concept
of the neutrino induced charge. The neutrino acquires a longitudinal and a
transverse charge, due to the fact that the form factors depend on the
transverse and longitudinal components of the photon momentum independently. We
compute those form factors explicitly in various limiting cases and find that
the longitudinal and transverse charge are the same for the case of a
non-relativistic electron gas, but not otherwise.Comment: 18 pages. Revtex4, axodra
Geotomography with solar and supernova neutrinos
We show how by studying the Earth matter effect on oscillations of solar and
supernova neutrinos inside the Earth one can in principle reconstruct the
electron number density profile of the Earth. A direct inversion of the
oscillation problem is possible due to the existence of a very simple analytic
formula for the Earth matter effect on oscillations of solar and supernova
neutrinos. From the point of view of the Earth tomography, these oscillations
have a number of advantages over the oscillations of the accelerator or
atmospheric neutrinos, which stem from the fact that solar and supernova
neutrinos are coming to the Earth as mass eigenstates rather than flavour
eigenstates. In particular, this allows reconstruction of density profiles even
over relatively short neutrino path lengths in the Earth, and also of
asymmetric profiles. We study the requirements that future experiments must
meet to achieve a given accuracy of the tomography of the Earth.Comment: 35 pages, 7 figures; minor textual changes in section
Cold Plus Hot Dark Matter Cosmology in the Light of Solar and Atmospheric Neutrino Oscillations
We explore the implications of possible neutrino oscillations, as indicated
by the solar and atmospheric neutrino experiments, for the cold plus hot dark
matter scenario of large scale structure formation. We find that there are
essentially three distinct schemes that can accommodate the oscillation data
and which also allow for dark matter neutrinos. These include (i) three nearly
degenerate (in mass) neutrinos, (ii) non-degenerate masses with in
the eV range, and (iii) nearly degenerate pair (in the eV
range), with the additional possibility that the electron neutrino is
cosmologically significant. The last two schemes invoke a `sterile' neutrino
which is light (< or ~ eV). We discuss the implications of these schemes for
and oscillation, and find
that scheme (ii) in particular, predicts them to be in the observable range. As
far as structure formation is concerned, we compare the one neutrino flavor
case with a variety of other possibilities, including two and three degenerate
neutrino flavors. We show, both analytically and numerically, the effects of
these neutrino mass scenarios on the amplitude of cosmological density
fluctuations. With a Hubble constant of 50 km s Mpc, a spectral
index of unity, and , the two and three flavor
scenarios fit the observational data marginally better than the single flavor
scheme. However, taking account of the uncertainties in these parameters, we
show that it is premature to pick a clear winner.Comment: 1 LaTEX file plus 1 uuencoded Z-compressed tar file with 3 postscript
figure
Attenuation effect and neutrino oscillation tomography
The attenuation effect is the effect of weakening contributions to the oscillation signal from remote structures of the 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, λatt, are not âseenâ at the level ΔâĄ2EV/Îm2, where V is the matter potential. We show that the origins of attenuation are (i) the averaging of oscillations in certain layer(s) of matter, (ii) the smallness of the matter effect: ΔâȘ1, and (iii) the specific initial and final states on neutrinos. We elaborate on the graphic description of the attenuation that allows us to compute explicitly the effects in the Δ2 order for various density profiles and oscillation channels. The attenuation in the case of partial averaging is described. The effect is crucial for the interpretation of oscillation data and for the oscillation tomography of the Earth with low energy (solar, supernova, atmospheric, etc.) neutrinos.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