Heavy sterile neutrinos and supernova explosions

We consider sterile neutrinos with rest masses 0.2 GeV and with vacuum flavor mixing angles θ²>10⁻⁸ for mixing with τ-neutrinos, or 10⁻⁸<θ²<10⁻⁷ for mixing with muon neutrinos. Such sterile neutrinos could augment core collapse supernova shock energies by enhancing energy transport from the core to the vicinity of the shock front. The decay of these neutrinos could produce a flux of very energetic active neutrinos, detectable by future neutrino observations from galactic supernova. The relevant range of sterile neutrino masses and mixing angles can be probed in future laboratory experiments.     

Physics opportunities with supernova neutrinos

The high-statistics neutrino signal from the next nearby supernova (SN) would provide a bonanza of astrophysical and particle-physics information. In particular, there are two new developments in this field: (i) The SASI instability can imprint potentially detectable short-time variations on the neutrino signal. (ii) Collective neutrino oscillations strongly modify the previous paradigm of SN neutrino oscillations with potentially detectable consequences.     

The response of Mo to supernova neutrinos

Knowledge about nuclear responses to neutrinos is essential for both astrophysical applications and studies of neutrino properties. We perform in this paper calculations of the cross sections for neutral-current neutrino scattering off the odd A=95,97 Mo isotopes for energies appropriate for the detection of supernova neutrinos. Both the incoherent and coherent contributions to the cross sections are evaluated. The prominently contributing nuclear final states are identified and analysed. We employ the microscopic quasiparticle-phonon model (MQPM) to construct the wave functions of the initial and final nuclear states. The response of the aforementioned nuclei to supernova neutrinos are computed by folding the obtained cross sections with a two-parameter Fermi-Dirac distribution. The sensitivity of the calculated nuclear responses to the adopted supernova model is also discussed.     

Towards the detection of light and heavy relic neutrinos

The standard Big Bang cosmology predicts that the universe is abundantly populated with neutrinos. As expected there are at least 114 neutrinos per cubic centimeter averaged over the whole space. Like the cosmic background radiation the cosmic neutrinos at present posses a very small kinetic energy due to expansion of the universe. This prediction is one of the cornerstones of modern cosmology. On the other hand the existence of cosmic neutrinos has not yet been confirmed by direct detection experiments. For now we only have a lower limit on the total mass of this free floating ghostly gas of neutrinos, but even so it is roughly equivalent to the total mass of all the visible stars in universe. There could be many more neutrinos at Earth because of condensation of neutrinos, now moving slowly under the gravitational pull of our galaxy. Here we discuss the possibility of detection of relic neutrinos in KATRIN and MARE experiments via neutrino capture on tritium and rhenium, respectively. We also examine single and double relic neutrino capture on double β-decaying nuclei which might be relevant in the context of the new generation double beta decay experiments. Further we explore feasibility of experiments for detection of heavy sterile neutrinos with masses in MeV region, which may have important astrophysical and cosmological implications.     

Phenomenological analysis of hybrid textures of neutrinos

We present a comprehensive phenomenological analysis of the allowed hybrid textures of neutrinos. Out of a total of sixty hybrid textures with one equality between the elements of neutrino mass matrix and one texture zero only twenty three are found to be viable at 99% C.L. whereas the earlier analysis found fifty four to be viable. We examine the phenomenological implications of the allowed hybrid textures including Majorana type CP-violating phases, 1–3 mixing angle and Dirac type CP-violating phase, δ. We, also, obtain lower bound on effective Majorana mass for all the allowed hybrid textures.     

Detection of supernova neutrinos at spallation neutron sources

After considering supernova shock effects, Mikheyev-Smirnov-Wolfenstein effects, neutrino collective effects, and Earth matter effects, the detection of supernova neutrinos at the China Spallation Neutron Source is studied and the expected numbers of different flavor supernova neutrinos observed through various reaction channels are calculated with the neutrino energy spectra described by the Fermi-Dirac distribution and the "beta fit"distribution respectively. Furthermore, the numerical calculation method of supernova neutrino detection on Earth is applied to some other spallation neutron sources, and the total expected numbers of supernova neutrinos observed through different reactions channels are given.     

Transmission of neutrinos through matter

Neutrinos travel through matter with negligible absorption except in very extreme situations. However, the index of refraction of neutrinos can play an important role in the oscillation of one type of neutrino to another when passing through matter.     

On the possibility to determine neutrino mass hierarchy via supernova neutrinos with short-time characteristics

In this paper, we investigate whether it is possible to determine the neutrino mass hierarchy via a high-statistics and real-time observation of supernova neutrinos with short-time characteristics. The essential idea is to utilize distinct times-of-flight for different neutrino mass eigenstates from a core-collapse supernova to the Earth, which may significantly change the time distribution of neutrino events in the future huge water-Cherenkov and liquid-scintillator detectors. For illustration, we consider two different scenarios. The first case is the neutronization burst of emitted in the first tens of milliseconds of a core-collapse supernova, while the second case is the black hole formation during the accretion phase for which neutrino signals are expected to be abruptly terminated. In the latter scenario, it turns out only when the supernova is at a distance of a few Mpc and the fiducial mass of the detector is at the level of gigaton, might we be able to discriminate between normal and inverted neutrino mass hierarchies. In the former scenario, the probability for such a discrimination is even less due to a poor statistics.     

Probing pseudo-Dirac neutrino through detection of neutrino-induced muons from gamma ray burst neutrinos

The possibility to verify the pseudo-Dirac nature of neutrinos is investigated here via the detection of ultra-high energy neutrinos from distant cosmological objects like γ-ray bursts (GRBs). The very long baseline and the energy range from ∼TeV to ∼EeV for such neutrinos invoke the likelihood to probe very small pseudo-Dirac splittings. The expected secondary muons from such neutrinos that can be detected by a kilometer scale detector such as ICECUBE is calculated and compared with the same in the case of mass-flavour oscillations and for no oscillation cases. The calculated muon yields indicate that to probe such small pseudo-Dirac splittings one needs to look for a nearby GRB (red shift z ∼ 0.03 or less) whereas for a distant GRB (z ∼ 1) the flux will be much depleted and such phenomenon cannot be distinguished. Also calculated are the muon-to-shower ratios.      

Contributed report: Flavor anarchy for Majorana neutrinos

We argue that neutrino flavor parameters may exhibit features that are very different from those of quarks and charged leptons. Specifically, within the Proggatt-Nielsen (FN) framework, charged fermion parameters depend on the ratio between two scales, while for neutrinos a third scale — that of lepton number breaking — is involved. Consequently, the selection rules for neutrinos may be different. In particular, if the scale of lepton number breaking is similar to the scale of horizontal symmetry breaking, neutrinos may become flavor-blind even if they carry different horizontal charges. This provides an attractive mechanism for neutrino flavor anarchy.     

Flavour mixing of neutrinos and baryon asymmetry of the universe

We investigate baryogenesis in the ν  MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when θ₁₃=0${\theta }_{13}=0$ and θ₂₃=π/4${\theta }_{23}=\pi /4$, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU.     

Neutrinos from CNO cycle at the present epoch of the solar neutrino research

The CNO cycle contributes only a small fraction to the energy generated in the Sun but there’s still no experimental data on exactly how small this contribution is. After the results of Borexino experiment the CNO neutrinos it is the last missing chain to compose the total picture of the energy generation of the Sun. To get precision in the evaluation of the flux of pp-neutrinos one needs to measure the flux of CNO neutrinos. Then it will be possible to address the question on the presence of still unknown (hidden) sources of solar energy and/or on the presence of sterile neutrinos. The future experimental program to measure the effect from CNO neutrinos is discussed.     

Search for heavy sterile neutrinos in trileptons at the LHC

We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of W~±→e~±e~±μ~?ν and μ~±μ~± e~?ν at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count(CC) and Multi-Variate Analysis(MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and discrimination limits. Two benchmark points with sterile neutrino mass m N =20 GeV and 50 GeV are tested. For an integrated luminosity of 3000 fb~(-1), sterile neutrinos can be found with 5σ significance if heavy-to-light neutrino mixings |U_(Ne)|~2~|U_(Nμ)|~2~10~(-6), while Majorana vs. Dirac discrimination can be reached if at least one of the mixings is of order 10~(-5).     

Absence of a day-night asymmetry in the Be solar neutrino rate in Borexino

We report the result of a search for a day-night asymmetry in the ⁷Be solar neutrino interaction rate in the Borexino detector at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The measured asymmetry is Adn=0.001±0.012 (stat)±0.007 (syst), in agreement with the prediction of MSW-LMA solution for neutrino oscillations. This result disfavors MSW oscillations with mixing parameters in the LOW region at more than 8.5 σ. This region is, for the first time, strongly disfavored without the use of reactor anti-neutrino data and therefore the assumption of CPT symmetry. The result can also be used to constrain some neutrino oscillation scenarios involving new physics.     

Time-modulation of entangled two-body weak decays with massive neutrinos

In recent experiments at the GSI, Darmstadt, time-modulated orbital Electron Capture (EC) decays of H-like ¹⁴⁰Pr⁵⁸⁺, ¹⁴²Pm⁶⁰⁺, and ¹²²I⁵²⁺ ions with one electron in the K-shell, coasting in the ESR storage ring with velocity β=0.71, were observed. The EC-branches show exponential decay curves time-modulated with period T=7.06(8) s and amplitude a=0.18(3) for ¹⁴⁰Pr decays, T=7.10(22) s and a=0.23(4) for ¹⁴²Pm decays, and T=6.04(6) s and a=0.19(3) for ¹²²I (preliminary) decays in the laboratory frame. The simultaneously measured β⁺ branch of ¹⁴²Pm shows no modulation with a<0.03. We discuss here as origin of the modulation quantum beats produced by the superposition of massive neutrino, mass eigenstates emitted in the entangled two body weak decay. From the modulation frequency a value for the difference of the quadratic mass values is deduced, which is 2.9 times larger than the value derived by the KamLAND antineutrino oscillation experiment. The origin of the small modulation amplitudes is discussed as the result of a partial restoration of the interference terms which are expected to cancel for the usual assumed unitarity of the neutrino flavor mixing matrix.     

Oscillation of Dirac and Majorana neutrinos from muon decay in the case of a general interaction

We analyse the possibility of distinguishing Dirac and Majorana neutrinos in future neutrino factory experiments in which neutrinos are produced in muon decay when, in addition to a vector type as in the SM, there are also scalar interactions. We check this possibility in an experiment with a near detector, where the observed neutrinos do not oscillate, and in a far detector, after the neutrino oscillations. Neglecting higher-order corrections, even neutrino observation in the near detector does not give a chance to differentiate their character. However, this possibility appears in the leading-order after the neutrino oscillations observed in far detector.     

Technique for direct eV-scale measurements of the Mu and tau neutrino masses using supernova neutrinos

Early black hole formation in a core-collapse supernova will abruptly truncate the neutrino fluxes. The sharp cutoff can be used to make model-independent time-of-flight neutrino mass tests. Assuming a neutrino luminosity of 10(52) erg/s per flavor at cutoff and a distance of 10 kpc, Super-Kamiokande can detect an electron neutrino mass as small as 1.8 eV, and the proposed OMNIS detector can detect mu and tau neutrino masses as small as 6 eV. We present the first technique with direct sensitivity to eV-scale mu and tau neutrino masses.