191 research outputs found
Neutrino flavor conversion in a neutrino background: single- versus multi-particle description
In the early Universe, or near a supernova core, neutrino flavor evolution
may be affected by coherent neutrino-neutrino scattering. We develop a
microscopic picture of this phenomenon. We show that coherent scattering does
not lead to the formation of entangled states in the neutrino ensemble and
therefore the evolution of the system can always be described by a set of
one-particle equations. We also show that the previously accepted formalism
overcounts the neutrino interaction energy; the correct one-particle evolution
equations for both active-active and active-sterile oscillations contain
additional terms. These additional terms modify the index of refraction of the
neutrino medium, but have no effect on oscillation physics.Comment: 12 pages, 3 figures, minor typos correcte
Comments on Neutrino Tests of Special Relativity
We point out that the assumption of Lorentz noninvariance examined recently
by Coleman and Glashow leads to neutrino flavor oscillations which are
phenomenologically equivalent to those obtained by assuming the neutrinos
violate the principle of equivalence. We then comment on the limits on Lorentz
noninvariance which can be derived from solar, atmospheric, and accelerator
neutrino experiments.Comment: 5 pages, Revte
Probing the matter term at long baseline experiments
We consider (\nu_\mu --> \nu_e) oscillations in long baseline experiments
within a three flavor framework. A non-zero measurement of this oscillation
probability implies that the (13) mixing angle `phi' is non-zero. We consider
the effect of neutrino propagation through the matter of earth's crust and show
that, given the constraints from solar neutrino and CHOOZ data, matter effects
enhance the mixing for neutrinos rather than for anti-neutrinos. We need data
from two different experiments with different baseline lengths (such as K2K and
MINOS) to distinguish matter effects unambiguously.Comment: 9 pages including three figure
Do many-particle neutrino interactions cause a novel coherent effect?
We investigate whether coherent flavor conversion of neutrinos in a neutrino
background is substantially modified by many-body effects, with respect to the
conventional one-particle effective description. We study the evolution of a
system of interacting neutrino plane waves in a box. Using its equivalence to a
system of spins, we determine the character of its behavior completely
analytically. We find that, if the neutrinos are initially in flavor
eigenstates, no coherent flavor conversion is realized, in agreement with the
effective one-particle description. This result does not depend on the size of
the neutrino wavepackets and therefore has a general character. The validity of
the several important applications of the one-particle formalism is thus
confirmed.Comment: 25 pages, 1 figur
Solar Neutrinos with Three Flavor Mixings
The recent 71Ga solar neutrino observation is combined with the 37Cl and
Kamiokande-II observations in an analysis for neutrino masses and mixings. The
allowed parameter region is found for matter enhanced mixings among all three
neutrino flavors. Distortions of the solar neutrino spectrum unique to three
flavors are possible and may be observed in continuing and next generation
experiments.Comment: August 1992 (Revised) PURD-TH-92-
Determining the sign of at long baseline neutrino experiments
Recently it is advocated that high intensity and low energy neutrino beams should be built to probe the mixing angle to
a level of a few parts in . Experiments using such beams will have better
signal to background ratio in searches for oscillations. We
propose that such experiments can also determine the sign of even
if the beam consists of {\it neutrinos} only. By measuring the transitions in two different energy ranges, the effects due to
propagation of neutrinos through earth's crust can be isolated and the sign of
can be determined. If the sensitivity of an experiment to
is , then the same experiment is automatically sensitive to matter
effects and the sign of for values of .Comment: Title changed and paper rewritten. 4 pages, 1 figure, revte
Matter effects in long baseline experiments, the flavor content of the heaviest (or lightest) neutrino and the sign of Delta m^2
The neutrinos of long baseline beams travel inside the Earth's crust where
the density is approximately rho = 2.8 g cm^-3. If electron neutrinos
participate in the oscillations, matter effects will modify the oscillation
probabilities with respect to the vacuum case. Depending on the sign of Delta
m^2 an MSW resonance will exist for neutrinos or anti-neutrinos with energy
approximately E_nu(res) = 4.7 |\Delta m^2|/(10^-3 eV^2) GeV. For Delta m^2 in
the interval indicated by the Super-Kamiokande experiment this energy range is
important for the proposed long baseline experiments.
For positive Delta m^2 the most important effects of matter are a 9% (25%)
enhancement of the transition probability P(nu_mu -> nu_e) for the KEK to
Kamioka (Fermilab to Minos and CERN to Gran Sasso) beam(s) in the energy region
where the probability has its first maximum, and an approximately equal
suppression of P(antinu_mu -> antinu_e). For negative Delta m^2 the effects for
neutrinos and anti-neutrinos are interchanged. Producing beams of neutrinos and
antineutrinos and measuring the oscillation probabilities for both (nu_mu ->
nu_e) and (antinu_mu -> antinu_e) transitions can solve the sign ambiguity in
the determination of Delta m^2.Comment: Latex, 28 pages, 12 postscript figure
Neutrino Decay and Atmospheric Neutrinos
We reconsider neutrino decay as an explanation for atmospheric neutrino
observations. We show that if the mass-difference relevant to the two mixed
states \nu_\mu and \nu_\tau is very small (< 10^{-4} eV^2), then a very good
fit to the observations can be obtained with decay of a component of \nu_\mu to
a sterile neutrino and a Majoron. We discuss how the K2K and MINOS
long-baseline experiments can distinguish the decay and oscillation scenarios.Comment: 9 pages, Revtex, uses epsf.sty, 3 postscript figures. Additions and
corrections to references, minor changes in the text and to some number
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