92 research outputs found
Hint of CPT Violation in Short-Baseline Electron Neutrino Disappearance
We analyzed the electron neutrino data of the Gallium radioactive source
experiments and the electron antineutrino data of the reactor Bugey and Chooz
experiments in terms of neutrino oscillations allowing for a CPT-violating
difference of the squared-masses and mixings of neutrinos and antineutrinos. We
found that the discrepancy between the disappearance of electron neutrinos
indicated by the data of the Gallium radioactive source experiments and the
limits on the disappearance of electron antineutrinos given by the data of
reactor experiments reveal a positive CPT-violating asymmetry of the effective
neutrino and antineutrino mixing angles (with a statistical significance of
about 3.5 sigma), whereas the squared-mass asymmetry is practically not
bounded.Comment: 4 page
Status of 3+1 Neutrino Mixing
We present an update of our analysis of short-baseline neutrino oscillation
data in the framework of 3+1 neutrino mixing taking into account the recent
update of MiniBooNE antineutrino data and the recent results of the MINOS
search for nu_mu disappearance into sterile neutrinos (the more complicated 3+2
neutrino mixing is not needed since the CP-violating difference between
MiniBooNE neutrino and antineutrino data has diminished). The results of our
fits of short-baseline neutrino oscillation data including the MiniBooNE
low-energy anomaly (now present both in the neutrino and antineutrino data)
leads to a strong tension between appearance and disappearance data. Hence, it
seems likely that the low-energy anomaly is not due to nu_mu -> nu_e
transitions. Excluding the MiniBooNE low-energy anomaly, appearance and
disappearance data are marginally compatible. The global analysis has the
best-fit point at Delta m^2_{41} about 5.6 eV^2, which is rather large in
comparison with cosmological bounds, but there are three regions within 1 sigma
at Delta m^2_{41} about 1.6, 1.2, 0.91 eV^2. We also show that the data on the
Gallium neutrino anomaly favor values of Delta m^2_{41} larger than about 1
eV^2.Comment: 10 pages. Changed title. Final version to be published in PR
Phenomenology of Light Sterile Neutrinos
After a short review of the current status of standard three-neutrino mixing, we consider its extension with the addition of one or two light sterile neutrinos which can explain the anomalies found in short-baseline neutrino oscillation experiments. We review the results of the global analyses of short-baseline neutrino oscillation data in 3+1, 3+2 and 3+1+1 neutrino mixing schemes
Short-Baseline Electron Neutrino Disappearance at a Neutrino Factory
We discuss short-baseline and very-short-baseline electron neutrino
disappearance at a neutrino factory. We take into account geometric effects,
such as from averaging over the decay straights, and the uncertainties of the
cross sections. We follow an approach similar to reactor experiments with two
detectors: we use two sets of near detectors at different distances to cancel
systematics. We demonstrate that such a setup is very robust with respect to
systematics, and can have excellent sensitivities to the effective mixing angle
and squared-mass splitting. In addition, we allow for CPT invariance violation,
which can be tested (depending on the parameters) up to a 0.1% level.Comment: 21 pages. Final version published in Phys. Rev. D80 (2009) 07300
Light sterile neutrinos and inflationary freedom
We perform a cosmological analysis in which we allow the primordial power spectrum of scalar perturbations to assume a shape that is different from the usual power-law predicted by the simplest models of cosmological inflation. We parameterize the free primordial power spectrum with a ``piecewise cubic Hermite interpolating polynomial'' (PCHIP). We consider a 3+1 neutrino mixing model with a sterile neutrino having a mass at the eV scale, which can explain the anomalies observed in short-baseline neutrino oscillation experiments. We find that the freedom of the primordial power spectrum allows to reconcile the cosmological data with a fully thermalized sterile neutrino in the early Universe. Moreover, the cosmological analysis gives us some information on the shape of the primordial power spectrum, which presents a feature around the wavenumber k=0.002 Mpc 121
The NOMAD Experiment : Status Report
The NOMAD experiment has been designed to search for neutrino-tau appearance
in the CERN wide-band neutrino beam . The detector is now completed and has
been further improved. All subdetectors are working well. The experiment, where
the search for oscillation is based on kinematical criteria, will reach the
sensitivity dm2 > 0.7 eV2 for maximal mixing and dm2 > 50 eV2 for mixing angles
sin2 2\theta > 3.8E-4 after 2 years of running, making possible to explore a
region of cosmological interest. Preliminary measurements are presented from
the 1994 and 1995 data samples.Comment: 5 pages, An invited talk at the IV International Workshop on
Theoretical and Phenomenological Aspects of Underground Physics TAUP'95,
Toledo (Spain). September 17-21,1995. To appear in Nucl. Phys. B (Proc.
Suppl.) Presented on behalf of the NOMAD Collaboration. Latex format
(including figures), 6 eps figures (tar'ed and gzip'ed
First Double-Chooz Results and the Reactor Antineutrino Anomaly
We investigate the possible effects of short-baseline antinu_e disappearance
implied by the reactor antineutrino anomaly on the Double-Chooz determination
of theta_{13} through the normalization of the initial antineutrino flux with
the Bugey-4 measurement. We show that the effects are negligible and the value
of theta_{13} obtained by the Double-Chooz collaboration is accurate only if
Delta m^2_{41} is larger than about 3 eV^2. For smaller values of Delta
m^2_{41} the short-baseline oscillations are not fully averaged at Bugey-4 and
the uncertainties due to the reactor antineutrino anomaly can be of the same
order of magnitude of the intrinsic Double-Chooz uncertainties.Comment: 4 page
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
Short-Baseline Electron Neutrino Disappearance, Tritium Beta Decay and Neutrinoless Double-Beta Decay
We consider the interpretation of the MiniBooNE low-energy anomaly and the
Gallium radioactive source experiments anomaly in terms of short-baseline
electron neutrino disappearance in the framework of 3+1 four-neutrino mixing
schemes. The separate fits of MiniBooNE and Gallium data are highly compatible,
with close best-fit values of the effective oscillation parameters Delta m^2
and sin^2 2 theta. The combined fit gives Delta m^2 >~ 0.1 eV^2 and 0.11 <
sin^2 2 theta < 0.48 at 2 sigma. We consider also the data of the Bugey and
Chooz reactor antineutrino oscillation experiments and the limits on the
effective electron antineutrino mass in beta-decay obtained in the Mainz and
Troitsk Tritium experiments. The fit of the data of these experiments limits
the value of sin^2 2 theta below 0.10 at 2 sigma. Considering the tension
between the neutrino MiniBooNE and Gallium data and the antineutrino reactor
and Tritium data as a statistical fluctuation, we perform a combined fit which
gives Delta m^2 \simeq 2 eV and 0.01 < sin^2 2 theta < 0.13 at 2 sigma.
Assuming a hierarchy of masses m_1, m_2, m_3 << m_4, the predicted
contributions of m_4 to the effective neutrino masses in beta-decay and
neutrinoless double-beta-decay are, respectively, between about 0.06 and 0.49
and between about 0.003 and 0.07 eV at 2 sigma. We also consider the
possibility of reconciling the tension between the neutrino MiniBooNE and
Gallium data and the antineutrino reactor and Tritium data with different
mixings in the neutrino and antineutrino sectors. We find a 2.6 sigma
indication of a mixing angle asymmetry.Comment: 14 pages; final version published in Phys.Rev.D82:053005,201
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