144 research outputs found
Momentum-dependent contributions to the gravitational coupling of neutrinos in a medium
When neutrinos travel through a normal matter medium, the electron neutrinos
couple differently to gravity compared to the other neutrinos, due to the
presence of electrons in the medium and the absence of the other charged
leptons. We calculate the momentum-dependent part of the matter-induced
gravitational couplings of the neutrinos under such conditions, which arise at
order , and determine their contribution to the neutrino dispersion
relation in the presence of a gravitational potential .
These new contributions vanish for the muon and tau neutrinos. For electron
neutrinos with momentum , they are of the order of the usual Wolfenstein
term times the factor , for high energy
neutrinos. In environments where the gravitational potential is substantial,
such as those in the vicinity of Active Galactic Nuclei, they could be the
dominant term in the neutrino dispersion relation. They must also be taken into
account in the analysis of possible violations of the Equivalence Principle in
the neutrino sector, in experimental settings involving high energy neutrinos
traveling through a matter background.Comment: Minor corrections in the references; one reference adde
Solar Neutrinos and the Violation of Equivalence Principle
In this Brief Report, a non-standard solution to the solar neutrino problem
is revisited. This solution assumes that neutrino flavors could have different
couplings to gravity, hence, the equivalence principle is violated in this
mechanism. The gravity induced mixing has the potential of accounting for the
current solar neutrino data from several experiments even for massless
neutrinos. We fit this solution to the total rate of neutrino events in the
SuperKamiokande detector together with the total rate from other detectors and
also with the most recent results of the SuperKamiokande results for the
recoil-electron spectrum.Comment: 6 pages, 4 figures, submitted to Phys.Rev.
An Investigation of Equivalence Principle Violations Using Solar Neutrino Oscillations in a Constant Gravitational Potential
Neutrino oscillations induced by a flavor-dependent violation of the Einstein
Equivalence Principle (VEP) have been recently considered as a suitable
explanation of the solar electron-neutrino deficiency. Unlike the MSW
oscillation mechanism, the VEP mechanism is dependent on a coupling to the
local background gravitational potential . We investigate the differences
which arise by considering three-flavor VEP neutrinos oscillating against fixed
background potentials, and against the radially-dependent solar potential. This
can help determine the sensitivity of the gravitationally-induced oscillations
to both constancy and size (order of magnitude) of . In particular, we
consider the potential of the local superculster, , in
light of recent work suggesting that the varying solar potential has no effect
on the oscillations. The possibility for arbitrarily large background
potentials in different cosmologies is discussed, and the effects of one such
potential () are considered.Comment: 12pp, LaTeX; 12 figures (bitmapped postscript); Submitted to Phys Rev
Neutrino Anomalies without Oscillations
I review explanations for the three neutrino anomalies (solar, atmospheric
and LSND) which go beyond the ``conventional'' neutrino oscillations induced by
mass-mixing. Several of these require non-zero neutrino masses as well.Comment: 14pages, LATEX format, 3 figure
Neutrino Oscillations Induced by Gravitational Recoil Effects
Quantum gravitational fluctuations of the space-time background, described by
virtual D branes, may induce neutrino oscillations if a tiny violation of the
Lorentz invariance (or a violation of the equivalence principle) is imposed. In
this framework, the oscillation length of massless neutrinos turns out to be
proportional to M/E^2, where E is the neutrino energy and M is the mass scale
characterizing the topological fluctuations in the vacuum. Such a functional
dependence on the energy is the same obtained in the framework of loop quantum
gravity.Comment: 5 pages, LaTex fil
Testing the Principle of Equivalence by Solar Neutrinos
We discuss the possibility of testing the principle of equivalence with solar
neutrinos. If there exists a violation of the equivalence principle quarks and
leptons with different flavors may not universally couple with gravity. The
method we discuss employs a quantum mechanical phenomenon of neutrino
oscillation to probe into the non-universality of the gravitational couplings
of neutrinos. We develop an appropriate formalism to deal with neutrino
propagation under the weak gravitational fields of the sun in the presence of
the flavor mixing. We point out that solar neutrino observation by the next
generation water Cherenkov detectors can improve the existing bound on
violation of the equivalence principle by 3-4 orders of magnitude if the
nonadiabatic Mikheyev-Smirnov-Wolfenstein mechanism is the solution to the
solar neutrino problem.Comment: Latex, 17 pages + 6 uuencoded postscript figures, KEK-TH-396,
TMUP-HEL-9402 (unnecessary one reference was removed
Signatures of heavy Majorana neutrinos and HERA's isolated lepton events
The graph of neutrinoless double beta decay is applied to HERA and
generalized to final states with any two charged leptons. Considered is the
case in which one of the two escapes typical identification criteria and the
case when a produced tau decays hadronically. Both possibilities give one
isolated lepton with high transverse momentum, hadronic activity and an
imbalance in transverse momentum. We examine the kinematical properties of
these events and compare them with the high p_T isolated leptons reported by
the H1 collaboration. Their positive charged muon events can be explained by
the ``double beta'' process and we discuss possibilities for the precise
determination which original final state produced the single isolated lepton.
To confirm our hypothesis one should search in the data for high pseudorapidity
and/or low p_T leptons or for additional separated jets.Comment: 19 pages with 14 figures, minor change
MeV neutrinos in double beta decay
The effect of Majorana neutrinos in the MeV mass range on the double beta
decay of various isotopes is studied on pure phenomenological arguments. By
using only experimental half life data, limits on the mixing parameter
of the order 10 can be derived. Also the possible
achievements of upcoming experiments and some consequences are outlined.Comment: 7 pages, 6 uudecoded EPS-figure
Solar neutrino results and Violation of the Equivalence Principle: An analysis of the existing data and predictions for SNO
Violation of the Equivalence Principle (VEP) can lead to neutrino oscillation
through the non-diagonal coupling of neutrino flavor eigenstates with the
gravitational field. The neutrino energy dependence of this oscillation
probability is different from that of the usual mass-mixing neutrino
oscillations. In this work we explore, in detail, the viability of the VEP
hypothesis as a solution to the solar neutrino problem in a two generation
scenario with both the active and sterile neutrino alternatives, choosing these
states to be massless. To obtain the best-fit values of the oscillation
parameters we perform a chi square analysis for the total rates of solar
neutrinos seen at the Chlorine (Homestake), Gallium (Gallex and SAGE),
Kamiokande, and SuperKamiokande (SK) experiments. We find that the goodness of
these fits is never satisfactory. It markedly improves, especially for VEP
transformation to sterile neutrinos, if the Chlorine result is excluded from
the analysis. The 1117-day SK data for recoil electron spectrum are also
examined for signals of VEP oscillations. For these fits, we consider
variations of the Standard Solar Model by allowing the absolute normalizations
of the 8B and hep neutrinos to vary. Here the fits are quite good but the best
fit values of the parameters are rather different from those from the total
rates fits. A combined fit to the total rates and recoil electron spectrum data
is also performed. We present the 90% confidence limit contours for all the
three analyses mentioned above. The best-fit parameters obtained from the
recoil electron spectrum and the combined analysis of rate and spectrum are
used to predict the charge current and scattering electron spectrum at SNO.Comment: Latex, minor changes in text and in fig.4 and fig.5, to be published
in Phys. Rev.
Improved limits on nuebar emission from mu+ decay
We investigated mu+ decays at rest produced at the ISIS beam stop target.
Lepton flavor (LF) conservation has been tested by searching for \nueb via the
detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays
was identified. We extract upper limits of the branching ratio for the LF
violating decay mu+ -> e+ \nueb \nu compared to the Standard Model (SM) mu+ ->
e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral
distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0).
These results improve earlier limits by one order of magnitude and restrict
extensions of the SM in which \nueb emission from mu+ decay is allowed with
considerable strength. The decay \mupdeb as source for the \nueb signal
observed in the LSND experiment can be excluded.Comment: 10 pages, including 1 figure, 1 tabl
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