413 research outputs found
Joint short- and long-baseline constraints on light sterile neutrinos
Recent studies provide evidence that long-baseline (LBL) experiments are sensitive to the extra CP phases involved with light sterile neutrinos, whose existence is suggested by several anomalous short-baseline (SBL) results. We show that, within the 3+1 scheme, the combination of the existing SBL data with the LBL results coming from the two currently running experiments, NO\u3bdA and T2K, enables us to simultaneously constrain two active-sterile mixing angles, \u3b814 and \u3b824, and two CP phases, \u3b413 61\u3b4 and \u3b414, although the information on the second CP phase is still weak. The two mixing angles are basically determined by the SBL data, while the two CP phases are constrained by the LBL experiments, once the information coming from the SBL setups is taken into account. We also assess the robustness or fragility of the estimates of the standard 3-flavor parameters in the more general 3+1 scheme. To this regard we find that (i) the indication of CP violation found in the 3-flavor analyses persists also in the 3+1 scheme, with \u3b413 61\u3b4 having still its best-fit value around 12\u3c0/2, (ii) the 3-flavor weak hint in favor of the normal hierarchy becomes even less significant when sterile neutrinos come into play, (iii) the weak indication of nonmaximal \u3b823 (driven by NO\u3bdA disappearance data) persists in the 3+1 scheme, where maximal mixing is disfavored at almost the 90% C.L. in both normal and inverted mass hierarchy, and (iv) the preference in favor of one of the two octants of \u3b823 found in the 3-flavor framework (higher octant for inverted mass hierarchy) is completely washed out in the 3+1 scheme
Updated Global 3+1 Analysis of Short-BaseLine Neutrino Oscillations
We present the results of an updated fit of short-baseline neutrino
oscillation data in the framework of 3+1 active-sterile neutrino mixing. We
first consider and disappearance in the light of the
Gallium and reactor anomalies. We discuss the implications of the recent
measurement of the reactor spectrum in the NEOS experiment, which
shifts the allowed regions of the parameter space towards smaller values of
. The beta-decay constraints allow us to limit the oscillation
length between about 2 cm and 7 m at for neutrinos with an energy of
1 MeV. We then consider the global fit of the data in the light of the LSND
anomaly, taking into account the constraints from and
disappearance experiments, including the recent data of the MINOS and IceCube
experiments. The combination of the NEOS constraints on and the
MINOS and IceCube constraints on lead to an unacceptable
appearance-disappearance tension which becomes tolerable only in a pragmatic
fit which neglects the MiniBooNE low-energy anomaly. The minimization of the
global in the space of the four mixing parameters ,
, , and leads to three allowed
regions with narrow widths at (best-fit), 1.3 (at ), 2.4 (at ) eV. The
restrictions of the allowed regions of the mixing parameters with respect to
our previous global fits are mainly due to the NEOS constraints. We present a
comparison of the allowed regions of the mixing parameters with the
sensitivities of ongoing experiments, which show that it is likely that these
experiments will determine in a definitive way if the reactor, Gallium and LSND
anomalies are due to active-sterile neutrino oscillations or not.Comment: 39 pages; improved treatment of the reactor flux uncertainties and
other minor correction
Short-Baseline Electron Neutrino Oscillation Length After Troitsk
We discuss the implications for short-baseline electron neutrino
disappearance in the 3+1 mixing scheme of the recent Troitsk bounds on the
mixing of a neutrino with mass between 2 and 100 eV. Considering the Troitsk
data in combination with the results of short-baseline nu_e and antinu_e
disappearance experiments, which include the reactor and Gallium anomalies, we
derive a 2 sigma allowed range for the effective neutrino squared-mass
difference between 0.85 and 43 eV^2. The upper bound implies that it is likely
that oscillations in distance and/or energy can be observed in radioactive
source experiments. It is also favorable for the ICARUS@CERN experiment, in
which it is likely that oscillations are not washed-out in the near detector.
We discuss also the implications for neutrinoless double-beta decay.Comment: 5 pages. Final version published in Phys.Rev. D87 (2013) 01300
Pragmatic View of Short-Baseline Neutrino Oscillations
We present the results of global analyses of short-baseline neutrino
oscillation data in 3+1, 3+2 and 3+1+1 neutrino mixing schemes. We show that
the data do not allow us to abandon the simplest 3+1 scheme in favor of the
more complex 3+2 and 3+1+1 schemes. We present the allowed region in the 3+1
parameter space, which is located at between 0.82 and 2.19
at . The case of no oscillations is disfavored by about
, which decreases dramatically to about if the LSND data are
not considered. Hence, new high-precision experiments are needed to check the
LSND signal.Comment: 6 pages. Final version published in Phys. Rev. D 88, 073008 (2013
Light sterile neutrinos
The theory and phenomenology of light sterile neutrinos at the eV mass scale
is reviewed. The reactor, Gallium and LSND anomalies are briefly described and
interpreted as indications of the existence of short-baseline oscillations
which require the existence of light sterile neutrinos. The global fits of
short-baseline oscillation data in 3+1 and 3+2 schemes are discussed, together
with the implications for beta-decay and neutrinoless double-beta decay. The
cosmological effects of light sterile neutrinos are briefly reviewed and the
implications of existing cosmological data are discussed. The review concludes
with a summary of future perspectives.Comment: 41 pages; final version to be published as a Topical Review in
Journal of Physics
Reactor Fuel Fraction Information on the Antineutrino Anomaly
We analyzed the evolution data of the Daya Bay reactor neutrino experiment in
terms of short-baseline active-sterile neutrino oscillations taking into
account the theoretical uncertainties of the reactor antineutrino fluxes. We
found that oscillations are disfavored at with respect to a
suppression of the reactor antineutrino flux and at
with respect to variations of the and
fluxes. On the other hand, the analysis of the rates of the
short-baseline reactor neutrino experiments favor active-sterile neutrino
oscillations and disfavor the suppression of the flux at
and variations of the and fluxes
at . We also found that both the Daya Bay evolution data and the
global rate data are well-fitted with composite hypotheses including variations
of the or fluxes in addition to
active-sterile neutrino oscillations. A combined analysis of the Daya Bay
evolution data and the global rate data shows a slight preference for
oscillations with respect to variations of the and
fluxes. However, the best fits of the combined data are given
by the composite models, with a preference for the model with an enhancement of
the flux and relatively large oscillations.Comment: 9 page
Massive neutrinos, Lorentz invariance dominated standard model and the phenomenological approach to neutrino oscillations
For the electroweak interactions, the massive neutrino perturbative
kinematical procedure is developed in the massive neutrino Fock space. This
yields the dominant Lorentz invariant Standard Model mass-less flavor neutrino
cross-sections as well as the neutrino oscillation cross-sections some of which
are Lorentz invariance and flavor conservation violating. But all these
oscillating cross-sections being proportional to the squares of neutrino masses
are practically unobservable in the laboratory; however, they are consistent
with the original Pontecorvo neutrino oscillating transition probability
expression at short time (baseline), as presented by Dvornikov. Then, by
mimicking the time dependence of the original Pontecorvo neutrino oscillating
transition probability, one can formulate the dimensionless neutrino
intensity-probability I, by phenomenological extrapolating the time t, or,
equivalently the baseline distance L away from the collision point for the
oscillating differential cross-section. For the incoming neutrino of 10MeV in
energy and neutrino masses from Fritzsch analysis with the neutrino mixing
matrix of Harrison, Perkins and Scott, the baseline distances at the first two
maxima of the neutrino intensity are L=281km and L=9279km . The intensity I at
the first maximum conserves the flavor, while at the second maximum; the
intensities violate the flavor, respectively, in the final and initial state.
At the end some details are given as to how these neutrino oscillations away
from the collision point one should be able to verify experimentally.Comment: 20 preprint, 9 published, page
- …