8,042 research outputs found
Search for Sub-eV Sterile Neutrinos in the Precision Multiple Baselines Reactor Antineutrino Oscillation Experiments
According to different effects on neutrino oscillations, the unitarity
violation in the MNSP matrix can be classified into the direct unitarity
violation and the indirect unitarity violation which are induced by the
existence of the light and the heavy sterile neutrinos respectively. Of which
sub-eV sterile neutrinos are of most interesting. We study in this paper the
possibility of searching for sub-eV sterile neutrinos in the precision reactor
antineutrino oscillation experiments with three different baselines at around
500 m, 2 km and 60 km. We find that the antineutrino survival probabilities
obtained in the reactor experiments are sensitive only to the direct unitarity
violation and offer very concentrated sensitivity to the two parameters
and . If such light sterile neutrinos do
exist, the active-sterile mixing angle could be acquired by
the combined rate analysis at all the three baselines and the mass-squared
difference could be obtained by taking the Fourier
transformation to the L / E spectrum. Of course, for such measurements to
succeed, both high energy resolution and large statistics are essentially
important.Comment: 19 RevTex pages, 7 figures. text structure rearranged, some figures
deleted, more discussions and references added; to be appear in NP
Proton Cumulants and Correlation Functions in Au + Au Collisions at =7.7-200 GeV from UrQMD Model
We studied the acceptance dependence of proton cumulants (up to fourth order)
and correlation functions in 0--5\% most central Au+Au collisions at
=7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV from UrQMD
model. We found that high order proton cumulants show suppressions at large
acceptance. By decomposing the proton cumulants into linear combination of
multi-proton correlation functions, we observed the two-proton correlation
functions always show negative values due to the effects of baryon number
conservations. The three and four-proton correlation functions are close to
zero and show negligible acceptance dependence. We further observed that the
proton cumulants and correlation functions follow similar trends and show a
scaling behavior when plotting the results versus mean number of protons. The
comparisons between experimental data and the UrQMD calculations show that the
non-monotonic energy dependence of proton correlation functions measured by
STAR experiment cannot be described by the UrQMD model. The UrQMD calculations
can provide us baselines for the experimental studies of the proton cumulants
and correlation functions. Finally, we propose to measure the rapidity
dependence of the reduced proton correlation functions to search for the QCD
critical point in heavy-ion collisions.Comment: 9 pages, 8 figures, Accepted by Physics Letters
Global Neutrino Heating in Hyperaccretion Flows
The neutrino-dominated accretion flow (NDAF) with accretion rates \dot{M} =
0.01 - 10 M_{\sun} s^{-1} is a plausible candidate for the central engine of
gamma-ray bursts (GRBs). This hyperaccretion disk is optically thin to
neutrinos in the radial direction, therefore the neutrinos produced at one
radius can travel for a long distance in the disk. Those neutrinos can thus be
absorbed with certain probability by the disk matter at the other radius and
heat the disk there. The effect of this "global neutrino heating" has been
ignored in previous works and is the focus of this paper. We find that around
the "ignition" radius r_{ign}, the global neutrino heating rate could be
comparable to or even larger than the local viscous heating rate thus must be
an important process. Two possible consequences are in order if the "global
neutrino heating" is taken into account: i) the temperature of the disk is
slightly raised and the "ignition" radius r_{ign} slightly shifts to a larger
radius, both lead to the increasing of the total neutrino flux; ii) what is
more interesting is that, the temperature of the ADAF just beyond r_{ign} may
be raised above the virial temperature thus the accretion will be suppressed.
In this case, the activity of the black hole is expected to oscillate between
an active and inactive phases. The timescale of the active phases is estimated
to be \sim 1 second. If the timescale of the inactive phase is comparable to or
less than this value, this intermittent activity may explain the slow
variability component of the GRBs. Self-consistent global calculations of NDAFs
with the "global neutrino heating" included are required in the future to more
precisely evaluate this effect.Comment: 9 pages, 5 figures; more discussions and references added; accepted
for publication in MNRA
Theoretical Overview on the Flavor Issues of Massive Neutrinos
We present an overview on some basic properties of massive neutrinos and
focus on their flavor issues, including the mass spectrum, flavor mixing
pattern and CP violation. The lepton flavor structures are explored by taking
account of the observed value of the smallest neutrino mixing angle
\theta_{13}. The impact of \theta_{13} on the running behaviors of other flavor
mixing parameters is discussed in some detail. The seesaw-induced enhancement
of the electromagnetic dipole moments for three Majorana neutrinos is also
discussed in a TeV seesaw scenario.Comment: References added. arXiv admin note: text overlap with
arXiv:1203.1672, arXiv:1201.2543, arXiv:1203.311
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