289 research outputs found

### LSND versus MiniBooNE: Sterile neutrinos with energy dependent masses and mixing?

Standard active--sterile neutrino oscillations do not provide a satisfactory
description of the LSND evidence for neutrino oscillations together with the
constraints from MiniBooNE and other null-result short-baseline oscillation
experiments. However, if the mass or the mixing of the sterile neutrino depends
in an exotic way on its energy all data become consistent. I explore the
phenomenological consequences of the assumption that either the mass or the
mixing scales with the neutrino energy as $1/E_\nu^r (r > 0)$. Since the
neutrino energy in LSND is about 40 MeV, whereas MiniBooNE operates at around 1
GeV, oscillations get suppressed in MiniBooNE and the two results become fully
compatible for $r\gtrsim 0.2$. Furthermore, also the global fit of all relevant
data improves significantly by exploring the different energy regimes of the
various experiments. The best fit $\chi^2$ decreases by 12.7 (14.1) units with
respect to standard sterile neutrino oscillations if the mass (mixing) scales
with energy.Comment: 18 pages, 3 figures, discussion extended, version to appear in JHE

### Is the effect of the Sun's gravitational potential on dark matter particles observable?

We consider the effect of the Sun's gravitational potential on the local
phase space distribution of dark matter particles, focusing on its implication
for the annual modulation signal in direct detection experiments. We perform a
fit to the modulation signal observed in DAMA/LIBRA and show that the allowed
region shrinks if Solar gravitational focusing (GF) is included compared to the
one without GF. Furthermore, we consider a possible signal in a generic future
direct detection experiment, irrespective of the DAMA/LIBRA signal. Even for
scattering cross sections close to the current bound and a large exposure of a
xenon target with 270 ton yr it will be hard to establish the presence of GF
from data. In the region of dark matter masses below 40 GeV an annual
modulation signal can be established for our assumed experimental setup,
however GF is negligible for low masses. In the high mass region, where GF is
more important, the significance of annual modulation itself is very low. We
obtain similar results for lighter targets such as Ge and Ar. We comment also
on inelastic scattering, noting that GF becomes somewhat more important for
exothermic scattering compared to the elastic case.Comment: 19 pages, 20 figures, 1 table, v2: added Fig. 3 for DAMA, and
comments on light target

### Sterile neutrino oscillations after first MiniBooNE results

In view of the recent results from the MiniBooNE experiment we revisit the
global neutrino oscillation fit to short-baseline neutrino data by adding one
or two sterile neutrinos with eV-scale masses to the three Standard Model
neutrinos, and for the first time we consider also the global fit with three
sterile neutrinos. Four-neutrino oscillations of the (3+1) type have been only
marginally allowed before the recent MiniBooNE results, and become even more
disfavored with the new data (at the level of $4\sigma$). In the framework of
so-called (3+2) five-neutrino mass schemes we find severe tension between
appearance and disappearance experiments at the level of more than $3\sigma$,
and hence no satistfactory fit to the global data is possible in (3+2) schemes.
This tension remains also when a third sterile neutrino is added, and the
quality of the global fit does not improve significantly in a (3+3) scheme. It
should be noted, however, that in models with more than one sterile neutrino
the MiniBooNE results are in perfect agreement with the LSND appearance
evidence, thanks to the possibility of CP violation available in such
oscillation schemes. Furthermore, if disappearance data are not taken into
account (3+2) oscillations provide an excellent fit to the full MiniBooNE
spectrum including the event excess at low energies.Comment: 30 pages, 12 figures, minor improvements of text and abstract,
summary table added, matches version to be published in Phys. Rev.

### On the determination of the leptonic CP phase

The combination of data from long-baseline and reactor oscillation
experiments leads to a preference of the leptonic CP phase $\delta_{\rm CP}$ in
the range between $\pi$ and $2\pi$. We study the statistical significance of
this hint by performing a Monte Carlo simulation of the relevant data. We find
that the distribution of the standard test statistic used to derive confidence
intervals for $\delta_{\rm CP}$ is highly non-Gaussian and depends on the
unknown true values of $\theta_{23}$ and the neutrino mass ordering. Values of
$\delta_{\rm CP}$ around $\pi/2$ are disfavored at between $2\sigma$ and
$3\sigma$, depending on the unknown true values of $\theta_{23}$ and the mass
ordering. Typically the standard $\chi^2$ approximation leads to over-coverage
of the confidence intervals for $\delta_{\rm CP}$. For the 2-dimensional
confidence region in the ($\delta_{\rm CP},\theta_{23}$) plane the usual
$\chi^2$ approximation is better justified. The 2-dimensional region does not
include the value $\delta_{\rm CP} = \pi/2$ up to the 86.3\% (89.2\%)~CL
assuming a true normal (inverted) mass ordering. Furthermore, we study the
sensitivity to $\delta_{\rm CP}$ and $\theta_{23}$ of an increased exposure of
the T2K experiment, roughly a factor 12 larger than the current exposure and
including also anti-neutrino data. Also in this case deviations from
Gaussianity may be significant, especially if the mass ordering is unknown.Comment: 25 pages, 12 figures. Matches version which is to appear in JHEP. New
appendix with the first anti-neutrino results from T2K is adde

### Determination of the neutrino mass ordering by combining PINGU and Daya Bay II

The relatively large measured value of theta_13 has opened various
possiblities to determine the neutrino mass ordering, among them using PINGU,
the low-energy extention of the IceCube neutrino telescope, to observe matter
effects in atmospheric neutrinos, or a high statistics measurment of the
neutrino energy spectrum at a reactor neutrino experiment with a baseline of
around 60 km, such as the Daya Bay II project. In this work we point out a
synergy between these two approaches based on the fact that when data are
analysed with the wrong neutrino mass ordering the best fit occurs at different
values of |Delta m^2_31| for PINGU and Daya Bay II. Hence, the wrong mass
ordering can be excluded by a mismatch of the values inferred for |Delta
m^2_31|, thanks to the excellent accuracy for Delta m^2_31 of both experiments.
We perform numerical studies of PINGU and Daya Bay II sensitivities and show
that the synergy effect may lead to a high significance determination of the
mass ordering even in situations where the individual experiments obtain only
poor sensitivity.Comment: 23 pages, 7 figures (15 eps files), typos and minor mistakes
corrected, final version to appear in JHE

### The LSND puzzle in the light of MiniBooNE results

I give a brief overview over various attempts to reconcile the LSND evidence for oscillations with all other global neutrino data, including the results from MiniBooNE. I discuss the status of oscillation schemes with one or more sterile neutrinos and comment on various exotic proposals

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