177 research outputs found
Oscillations of high energy neutrinos in matter: Precise formalism and parametric resonance
We present a formalism for precise description of oscillation phenomena in
matter at high energies or high densities, V > \Delta m^2/2E, where V is the
matter-induced potential of neutrinos. The accuracy of the approximation is
determined by the quantity \sin^2 2\theta_m \Delta V/2\pi V, where \theta_m is
the mixing angle in matter and \Delta V is a typical change of the potential
over the oscillation length (l \sim 2\pi/V). We derive simple and physically
transparent formulas for the oscillation probabilities, which are valid for
arbitrary matter density profiles. They can be applied to oscillations of high
energy (E > 10 GeV) accelerator, atmospheric and cosmic neutrinos in the matter
of the Earth, substantially simplifying numerical calculations and providing an
insight into the physics of neutrino oscillations in matter. The effect of
parametric enhancement of the oscillations of high energy neutrinos is
considered. Future high statistics experiments can provide an unambiguous
evidence for this effect.Comment: LaTeX, 5 pages, 1 figure. Linestyles in the figure corrected to match
their description in the caption; improved discussion of the accuracy of the
results; references added. Results and conclusions unchange
Solar Neutrino Data, Neutrino Magnetic Moments and Flavor Mixing
The results of all currently operating solar neutrino experiments are
analyzed in the framework of the resonant neutrino spin--flavor precession
scenario including the effects of neutrino mixing. Nine different profiles of
the solar magnetic field are used in the calculations. It is shown that the
available experimental data can be accounted for within the considered
scenario. The Ga--Ge data lead to an upper limit on the neutrino mixing angle:
\sin 2\theta_0 \aprle 0.25. One can discriminate between small mixing angle
(\sin 2\theta_0 \aprle 0.1) and moderate mixing angle solutions by studying
the solar flux which is predicted to be sizeable for moderate
mixing angles. The expected signals due to in the SNO,
Super--Kamiokande and Borexino experiments are calculated and found to be
detectable for \sin 2\theta_0 \aprge 0.1.Comment: 16 pages, latex, 5 figures available upon request from Author
Neutrino production coherence and oscillation experiments
Neutrino oscillations are only observable when the neutrino production,
propagation and detection coherence conditions are satisfied. In this paper we
consider in detail neutrino production coherence, taking \pi\to \mu \nu \ decay
as an example. We compare the oscillation probabilities obtained in two
different ways: (1) coherent summation of the amplitudes of neutrino production
at different points along the trajectory of the parent pion; (2) averaging of
the standard oscillation probability over the neutrino production coordinate in
the source. We demonstrate that the results of these two different approaches
exactly coincide, provided that the parent pion is considered as pointlike and
the detection process is perfectly localized. In this case the standard
averaging of the oscillation probability over the finite spatial extensions of
the neutrino source (and detector) properly takes possible decoherence effects
into account. We analyze the reason for this equivalence of the two approaches
and demonstrate that for pion wave packets of finite width \sigma_{x\pi} the
equivalence is broken. The leading order correction to the oscillation
probability due to \sigma_{x\pi}\ne 0 is shown to be \sim
[v_g/(v_g-v_\pi)]\sigma_{x\pi}/l_{osc}, where v_g and v_\pi \ are the group
velocities of the neutrino and pion wave packets, and l_{osc} is the neutrino
oscillation length.Comment: LaTeX, 40 pages, 4 figures. v2: minor typos correcte
On the evolution of an entangled lepton-neutrino pair
The evolution of the entangled muon-neutrino system emerging from charged
pion decay is explored both in vacuum and in matter. The study is based on a
Weisskopf-Wigner type wave-packet description. Explicit formulae are derived
displaying modulation and attenuation of the oscillations due to additional
time scales characterising the production process. The case of neutrinos
disentangled due to the detection of the muon is also considered
Beta decay and other processes in strong electromagnetic fields
We consider effects of the fields of strong electromagnetic waves on various
characteristics of quantum processes. After a qualitative discussion of the
effects of external fields on the energy spectra and angular distributions of
the final-state particles as well as on the total probabilities of the
processes (such as decay rates and total cross sections), we present a simple
method of calculating the total probabilities of processes with production of
non-relativistic charged particles. Using nuclear beta-decay as an example, we
study the weak and strong field limits, as well as the field-induced beta-decay
of nuclei stable in the absence of the external fields, both in the tunneling
and multi-photon regimes. We also consider the possibility of accelerating
forbidden nuclear beta-decays by lifting the forbiddeness due to the
interaction of the parent or daughter nuclei with the field of a strong
electromagnetic wave. It is shown that for currently attainable electromagnetic
fields all effects on total beta-decay rates are unobservably small.Comment: LaTeX, 30 pages, 2 figures. Invited contribution to the special issue
of Yadernaya Fizika dedicated to the centennial anniversary of birthday of
A.B. Migdal. V2: references adde
Chizhov and Petcov Reply
We have found in [1] new conditions for a total neutrino conversion in the
case of neutrino oscillations taking place in a medium, consisting of n = 2 (or
3) alternating layers with constant densities and . It is claimed in
[4] that our results are particular case of enhancement of neutrino
oscillations, which was suggested earlier by other authors and was widely
discussed in the literature. We refute these claims, confirming the novelty of
our results.Comment: 2 pages, LATEX; concise (essentially 1 page) and somewhat modified
version of Ref. SISSA 5/2000/EP (hep-ph/0003110); reply on the ``Comment on
New Conditions for a Total Neutrino Conversion in a Medium'', Phys. Rev.
Lett. 85 (2000) 3978; published as ``Chizhov and Petcov Reply'' in Phys. Rev.
Lett. 85 (2000) 397
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
Neutrinos with Mixing in Twisting Magnetic Fields
Transitions in a system of neutrinos with vacuum mixing and magnetic moments,
propagating in matter and transverse magnetic field, are considered. It is
shown that in the realistic case of magnetic field direction varying along the
neutrino path qualitatively new phenomena become possible: permutation of
neutrino conversion resonances, appearance of resonances in the
neutrino-antineutrino () transition
channels, neutrino-antineutrino resonant conversion, large amplitude
oscillations, merging of different
resonances (triple resonances). Possible phenomenological implications of these
effects are briefly discussed.Comment: LaTeX, 35 pages, 4 figures (not included but available upon request).
In memoriam of Ya.A. Smorodinsky. SISSA-170/92/E
A diagrammatic treatment of neutrino oscillations
We present a covariant wave-packet approach to neutrino flavor transitions in
vacuum. The approach is based on the technique of macroscopic Feynman diagrams
describing the lepton number violating processes of production and absorption
of virtual massive neutrinos at the macroscopically separated space-time
regions ("source" and "detector"). Accordingly, the flavor transitions are a
result of interference of the diagrams with neutrinos of different masses in
the intermediate states. The statistically averaged probability of the process
is representable as a multidimensional integral of the product of the factors
which describe the differential flux density of massless neutrinos from the
source, differential cross section of the neutrino interaction with the
detector and a dimensionless factor responsible for the flavor transition. The
conditions are analyzed under which the last factor can be treated as the
flavor transition probability in the usual quantum-mechanical sense.Comment: 27 pages,7 figures, iopart class. Includes minor corrections made in
proofs. References update
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