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 $\theta^{}_{14}$ and $\Delta m^{2}_{41}$. If such light sterile neutrinos do exist, the active-sterile mixing angle $\theta^{}_{14}$ could be acquired by the combined rate analysis at all the three baselines and the mass-squared difference $\Delta m^{2}_{41}$ 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 sNN\sqrt{s_\mathrm{NN}}=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 $\sqrt{s_\text{NN}}$=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