434 research outputs found
The Physical Significance of Confidence Intervals
We define some appropriate statistical quantities that indicate the physical
significance (reliability) of confidence intervals in the framework of both
Frequentist and Bayesian statistical theories. We consider the expectation
value of the upper limit in the absence of a signal (that we propose to call
"exclusion potential", instead of "sensitivity" as done by Feldman and Cousins)
and its standard deviation, we define the "Pull" of a null result, expressing
the reliability of an experimental upper limit, and the "upper and lower
detection functions", that give information on the possible outcome of an
experiment if there is a signal. We also give a new appropriate definition of
"sensitivity", that quantifies the capability of an experiment to reveal the
signal that is searched for at the given confidence level.Comment: 16 page
The Power of Confidence Intervals
We consider the power to reject false values of the parameter in Frequentist
methods for the calculation of confidence intervals. We connect the power with
the physical significance (reliability) of confidence intervals for a parameter
bounded to be non-negative. We show that the confidence intervals (upper
limits) obtained with a (biased) method that near the boundary has large power
in testing the parameter against larger alternatives and small power in testing
the parameter against smaller alternatives are physically more significant.
Considering the recently proposed methods with correct coverage, we show that
the physical significance of upper limits is smallest in the Unified Approach
and highest in the Maximum Likelihood Estimator method. We illustrate our
arguments in the specific cases of a bounded Gaussian distribution and a
Poisson distribution with known background.Comment: 13 pages, 5 figure
Light Sterile Neutrinos in Cosmology and Short-Baseline Oscillation Experiments
We analyze the most recent cosmological data, including Planck, taking into
account the possible existence of a sterile neutrino with a mass at the eV
scale indicated by short-baseline neutrino oscillations data in the 3+1
framework. We show that the contribution of local measurements of the Hubble
constant induces an increase of the value of the effective number of
relativistic degrees of freedom above the Standard Model value, giving an
indication in favor of the existence of sterile neutrinos and their
contribution to dark radiation. Furthermore, the measurements of the local
galaxy cluster mass distribution favor the existence of sterile neutrinos with
eV-scale masses, in agreement with short-baseline neutrino oscillations data.
In this case there is no tension between cosmological and short-baseline
neutrino oscillations data, but the contribution of the sterile neutrino to the
effective number of relativistic degrees of freedom is likely to be smaller
than one. Considering the Dodelson-Widrow and thermal models for the
statistical cosmological distribution of sterile neutrinos, we found that in
the Dodelson-Widrow model there is a slightly better compatibility between
cosmological and short-baseline neutrino oscillations data and the required
suppression of the production of sterile neutrinos in the early Universe is
slightly smaller.Comment: 12 pages; final version published in JHEP 1311 (2013) 21
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
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 .Comment: 19 pages; corrected Fig.4 and added Ref.[35
The flavor of neutrinos in muon decays at a neutrino factory and the LSND puzzle
The accurate prediction of the neutrino beam produced in muon decays and the
absence of opposite helicity contamination for a particular neutrino flavor
make a future neutrino factory the ideal place to look for the lepton flavor
violating (LFV) decays of the kind \mu^+\ra e^+\nuebar\numu and lepton number
violating (LNV) processes like \mu^-\ra e^-\nue\numu. Excellent sensitivities
can be achieved using a detector capable of muon and/or electron identification
with charge discrimination. This would allow to set experimental limits that
improve current ones by more than two orders of magnitude and test the
hypothesis that the LSND excess is due to such anomalous decays, rather than
neutrino flavor oscillations in vacuum.Comment: 19 pages, 4 figure
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
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