Neutrino Burst Research Articles

Heavy sterile neutrino emission in core-collapse supernovae: constraints and signatures

Heavy sterile neutrinos with masses \U0001d4aa(100) MeV mixing with active neutrinos can be produced in the core of a collapsing supernova (SN). In order to avoid an excessive energy loss, shortening the observed duration of the SN 1987A neutrino burst, we show that the active-sterile neutrino mixing angle should satisfy sin2 θ ≲ 5 × 10−7. For a mixing with tau flavour, this bound is much stronger than the ones from laboratory searches. Moreover, we show that in the viable parameter space the decay of such “heavy” sterile neutrinos in the SN envelope would lead to a very energetic flux of daughter active neutrinos; if not too far below current limits, this would be detectable in large underground neutrino observatories, like Super-Kamiokande, as a (slightly time-delayed) high-energy bump in the spectrum of a forthcoming Galactic SN event.

Supernova Neutrinos at the DUNE Experiment

The Deep Underground Neutrino Experiment (DUNE) experiment, a 40-kton underground liquid argon time-projection-chamber detector, will have unique sensitivity to the electron flavor component of a core-collapse supernova neutrino burst. We present the expected capabilities of DUNE for measurements of neutrinos in the few-tens-of-MeV range relevant for supernova detection and its corresponding sensitivity to both neutrino physics and supernova astrophysics. Recent progress and some outstanding issues are highlighted.

Astrophyisical Neutrino in Hyper-Kamiokande

Hyper-Kamiokande (Hyper-K) is a proposed next generation underground large water Cherenkov detector. We plan to build two cylindrical water tanks in our experimental period, filled with ultra pure water and surrounded with newly developed photo sensors. In total, it will provide the fiducial volume of 0.19-0.37 Mt. The energies, positions, directions and types of charged particles produced by neutrino interactions are detected using its Cherenkov light in water. Our detector will be located at deep underground to reduce the cosmic muon flux and its spallation products, which is a dominant background for the analysis of the low energy astrophysical neutrinos.With the fruitful physics research programs planned for the accelerator neutrinos, atomospheric neutrinos and nucleon decay, Hyper-K will play an important role in the next neutrino physics frontier, even in the neutrino astrophysics. It will provide remarkable information for both of particle physics and astrophysics with its large statistics of astrophysical neutrino measurements, i.e., solar neutrino, supernova burst neutrinos and supernova relic neutrino. Here, we will discuss about physics potential of Hyper-K neutrino astrophysics and expected performance of the detector.

Supernova neutrino burst monitor at the Baksan Underground Scintillation Telescope

The experiment on recording neutrino bursts operates since the mid-1980. As a target, we use two parts of the facility with a total mass of 240 tons. The current status of the experiment and some results related to the investigation of background events and the stability of facility operation are presented. Over the period of June 30, 1980 to December 31, 2018, the actual observational time is 33.02 years. No candidate for the stellar core collapse has been detected during the observation period. The corresponding upper bound of the mean frequency of core collapse supernovae in our Galaxy is 0.070 year−1 (90% CL).

Accretion‐induced collapse to third family compact stars as trigger for eccentric orbits of millisecond pulsars in binaries

AbstractA numerical rotating neutron star solver is used to study the temporal evolution of accreting neutron stars using a multi‐polytrope model for the nuclear equation of state named ACB5. The solver is based on a quadrupole expansion of the metric, but confirms the results of previous works, revealing the possibility of an abrupt transition of a neutron star from a purely hadronic branch to a third‐family branch of stable hybrid stars, passing through an unstable intermediate branch. The accretion is described through a sequence of stationary rotating stellar configurations which lose angular momentum through magnetic dipole emission, while, at the same time, gaining angular momentum through mass accretion. The model has several free parameters which are inferred from observations. The mass accretion scenario is studied in dependence on the effectiveness of angular momentum transfer which determines at which spin frequency the neutron star will become unstable against gravitational collapse to the corresponding hybrid star on the stable third‐family branch. It is conceivable that the neutrino burst which accompanies the deconfinement transition may trigger a pulsar kick which results in the eccentric orbit. A consequence of the present model is the prediction of a correlation between the spin frequency of the millisecond pulsar in the eccentric orbit and its mass at birth.

Status of the Jiangmen Underground Neutrino Observatory

The Jiangmen Underground Neutrino Observatory (JUNO) is a next generation multipurpose antineutrino detector currently under construction in Jiangmen, China. The central detector, containing 20 kton of a liquid scintillator, will be equipped with ∼18 000 20 inch and 25 600 3 inch photomultiplier tubes. Measuring the reactor antineutrinos of two powerplants at a baseline of 53 km with an unprecedented energy resolution of 3%/√︀E(MeV), the main physics goal is to determine the neutrino mass hierarchy within six years of run time with a significance of 3–4q. Additional physics goals are the measurement of solar neutrinos, geoneutrinos, supernova burst neutrinos, the diffuse supernova neutrino background, and the oscillation parameters sin2 O12, Δm212, and |Δm2ee| with a precision <1%, as well as the search for proton decays. The construction is expected to be completed in 2021.

Akmal-Pandharipande-Ravenhall equation of state for simulations of supernovae, neutron stars, and binary mergers

Differences in the equation of state (EOS) of dense matter translate into differences in astrophysical simulations and their multimessenger signatures. Thus, extending the number of EOSs for astrophysical simulations allows us to probe the effect of different aspects of the EOS in astrophysical phenomena. In this work, we construct the EOS of hot and dense matter based on the Akmal, Pandharipande, and Ravenhall (APR) model and thereby extend the open-source SROEOS code which computes EOSs of hot dense matter for Skyrme-type parametrizations of the nuclear forces. Unlike Skrme-type models, in which parameters of the interaction are fit to reproduce the energy density of nuclear matter and/or properties of heavy nuclei, the EOS of APR is obtained from potentials resulting from fits to nucleon-nucleon scattering and properties of light nuclei. In addition, this EOS features a phase transition to a spin-isospin ordered state of nucleons, termed a neutral pion condensate, at supranuclear densities. We show that differences in the effective masses between EOSs have consequences for the properties of nuclei in the subnuclear inhomogeneous phase of matter. We also test the new EOS of APR in spherically symmetric core-collapse of massive stars with $15\phantom{\rule{0.28em}{0ex}}{M}_{\ensuremath{\bigodot}}$ and $40\phantom{\rule{0.28em}{0ex}}{M}_{\ensuremath{\bigodot}}$, respectively. We find that the phase transition in the EOS of APR speeds up the collapse of the star. However, this phase transition does not generate a second shock wave or another neutrino burst as reported for the hadron-to-quark phase transition. The reason for this difference is that the width of the coexistence region and the latent heat in the EOS of APR are substantially smaller than in the quark-to-hadron transition employed earlier, which results in a significantly smaller softening of the high density EOS.

The Search for Neutrino Bursts at the Baksan Underground Scintillation Telescope: 37 Years of Exposure

The search for neutrino bursts at the Baksan Underground Scintillation Telescope began in the middle of 1980. Two parts of the setup with a total mass of 240 t are used as the target. The actual observational time accumulated in the period from June 30, 1980, to December 31, 2017, is 32.1 years. No neutrino burst candidate events were detected, yielding the following upper bound for the mean rate of core-collapse supernovas in the Milky Way: 0.072 yr−1 (90% CL).

Neutrino flavor as a test of the explosion mechanism of core-collapse supernovae

We study the ratio of neutrino-proton elastic scattering to inverse beta decay event counts, measurable in a scintillation detector like JUNO, as a key observable for identifying the explosion mechanism of a galactic core-collapse supernova. If the supernova is not powered by the core but rather, e.g., by collapse-induced thermonuclear explosion, then a prolonged period of accretion-dominated neutrino luminosity is predicted. Using 1D numerical simulations, we show that the distinct resulting flavour composition of the neutrino burst can be tested in JUNO with high significance, overcoming theoretical uncertainties in the progenitor star profile and equation of state.

Developing the MeV potential of DUNE: Detailed considerations of muon-induced spallation and other backgrounds

The Deep Underground Neutrino Experiment (DUNE) could be revolutionary for MeV neutrino astrophysics, because of its huge detector volume, unique event reconstruction capabilities, and excellent sensitivity to the $\nu_e$ flavor. However, its backgrounds are not yet known. A major background is expected due to muon spallation of argon, which produces unstable isotopes that later beta decay. We present the first comprehensive study of MeV spallation backgrounds in argon, detailing isotope production mechanisms and decay properties, analyzing beta energy and time distributions, and proposing experimental cuts. We show that above a nominal detection threshold of 5-MeV electron energy, the most important backgrounds are --- surprisingly --- due to low-A isotopes, such as Li, Be, and B, even though high-A isotopes near argon are abundantly produced. We show that spallation backgrounds can be powerfully rejected by simple cuts, with clear paths for improvements. We compare these background rates to rates of possible MeV astrophysical neutrino signals in DUNE, including solar neutrinos (detailed in a companion paper [Capozzi et al. arXiv:1808.08232 [hep-ph]]), supernova burst neutrinos, and the diffuse supernova neutrino background. Further, to aid trigger strategies, in the Appendixes we quantify the rates of single and multiple MeV events due to spallation, radiogenic neutron capture, and other backgrounds, including through pileup. Our overall conclusion is that DUNE has high potential for MeV neutrino astrophysics, but reaching this potential requires new experimental initiatives.

The ν-process with Fully Time-dependent Supernova Neutrino Emission Spectra

Abstract The neutrino process that occurs in the outer stellar shells during a supernova explosion and involves neutrino–nucleus reactions produces a range of rare, stable, and radioactive isotopes. We improve previous ν-process studies by using, for the first time, the time-dependent neutrino emission spectra, as predicted from supernova simulations, rather than a simplified parametric description modeled after the neutron star cooling phase. In particular, our calculations use time-dependent neutrino spectra for all neutrino species, consider their deviation from a Fermi–Dirac distribution, and account for the neutrino emission from the neutrino burst and accretion phases. We find that the time-dependent treatment of the neutrino emission spectra results in higher yields for the selected nuclei produced by the ν process as compared to previous studies and to the approximation of assuming constant neutrino energies corresponding to the time-averaged mean energy radiated in each species. The effect is largest for nuclides produced by charged-current reactions. Our results reflect the dynamical competition between neutrino-induced reactions and the effect of the shock passage through the star. By varying the neutrino burst luminosity and the duration of the accretion phase, we study the impact of these early emission phases and their uncertainties on the ν-process nucleosynthesis. We find that the deviation of the neutrino spectra from a Fermi–Dirac distribution calculated in supernova simulations has a negligible effect on the ν-process yields.

Study of the Low-Energy Background Variations in the LVD Underground Experiment

The underground Large Volume Detector (LVD) has been in operation at the Gran Sasso National Laboratory since 1992. The research program includes a search for neutrino bursts from stellar core colapses, studies of the cosmic ray penetrating component, and investigations of background sources at detecting rare events. In this work, the low-energy background (E > 0.5 MeV) in the LVD experiment is analyzed.

The search for rare events using Large Volume Detector

The results of the searching for rare events in the Large Volume Detector (LVD) are presented. The rare events could be caused by neutrino interactions in the experimental setup. In the work, the experimental data for 2006-2017 are analyzed. A stability of LVD background counting rate during the specified period is shown. Candidates on neutrino bursts from collapsing stars in the sequence of the LVD events are not found.

A search for neutrino bursts in the Galaxy at the Baksan Underground Scintillation Telescope

The experiment on recording neutrino bursts operates since the mid-1980. As the target, we use two parts of the facility with the total mass of 240 tons. Over the period of June 30, 1980 to December 31, 2017, the actual observational time is 32.1 years. No candidate for the stellar core collapse has been detected during the observation period. An upper bound of the mean frequency of core collapse supernovae in our Galaxy is 0.072 year−1 (90% CL).

Comparing Treatments of Weak Reactions with Nuclei in Simulations of Core-collapse Supernovae

Abstract We perform an extensive study of the influence of nuclear weak interactions on core-collapse supernovae, paying particular attention to consistency between nuclear abundances in the equation of state (EOS) and nuclear weak interactions. We compute properties of uniform matter based on the variational method. For inhomogeneous nuclear matter, we take a full ensemble of nuclei into account with various finite-density and thermal effects and directly use the nuclear abundances to compute nuclear weak interaction rates. To quantify the impact of a consistent treatment of nuclear abundances on CCSN dynamics, we carry out spherically symmetric CCSN simulations with full Boltzmann neutrino transport, systematically changing the treatment of weak interactions, EOSs, and progenitor models. We find that the inconsistent treatment of nuclear abundances between the EOS and weak interaction rates weakens the EOS dependence of both the dynamics and neutrino signals. We also test the validity of two artificial prescriptions for weak interactions of light nuclei and find that both prescriptions affect the dynamics. Furthermore, there are differences in neutrino luminosities by ∼10% and in average neutrino energies by 0.25–1 MeV from those of the fiducial model. We also find that the neutronization burst neutrino signal depends on the progenitor more strongly than on the EOS, preventing a detection of this signal from constraining the EOS.

Review of the Empirical Evidence for Superluminal Particles and the 3 + 3 Model of the Neutrino Masses

A review is given of hypothetical faster-than-light tachyons and the development of the author’s 3+3 model of the neutrino mass states, which includes one tachyonic mass state doublet. Published empirical evidence for the model is summarized, including an interpretation of the mysterious Mont Blanc neutrino burst from SN 1987A as being due to tachyonic neutrinos having m2=-0.38eV2. This possibility requires an 8 MeV antineutrino line from SN 1987A, which a new dark matter model has been found to support. Furthermore, this dark matter model is supported by several datasets: γ-rays from the galactic center, and the Kamiokande-II neutrino data on the day of SN 1987A. The KATRIN experiment should serve as the unambiguous test of the 3+3 model and its tachyonic mass state.

Charged-current scattering off the 16O nucleus as a detection channel for supernova neutrinos

Event spectra of the neutrino-$^{16}$O charged-current reactions in Super-Kamiokande are evaluated for a future supernova neutrino burst. Since these channels are expected to be useful for diagnosing a neutrino spectrum with high average energy, the evaluations are performed not only for an ordinary supernova neutrino model but also for a model of neutrino emission from a black-hole-forming collapse. Using shell model results, whose excitation energies are consistent with the experimental data, the cross sections of the $^{16}$O($\nu_e, e^-$)X and $^{16}$O($\bar\nu_e, e^+$)X reactions for each nuclear state with a different excitation energy are employed in this study. It is found that, owing to the components of the reaction with higher excitation energy, the event spectrum becomes 4-7 MeV softer than that in the case without considering the excitation energies. In addition, a simplified approach to evaluate the event spectra is proposed for convenience and its validity is examined.

The search for high-energy neutrinos coincident with fast radio bursts with the ANTARES neutrino telescope

In the past decade, a new class of bright transient radio sources with millisecond duration has been discovered. The origin of these so-called Fast Radio Bursts (FRBs) is still a great mystery despite the growing observational efforts made by various multi-wavelength and multi-messenger facilities. So far, many models have been proposed to explain FRBs but neither the progenitors nor the radiative and the particle acceleration processes at work have been clearly identified. In this paper, the question whether some hadronic processes may occur in the vicinity of the FRB source is assessed. If so, FRBs may contribute to the high energy cosmic-ray and neutrino fluxes. A search for these hadronic signatures has been done using the ANTARES neutrino telescope. The analysis consists in looking for high-energy neutrinos, in the TeV-PeV regime, spatially and temporally coincident with the detected FRBs. Most of the FRBs discovered in the period 2013-2017 were in the field of view of the ANTARES detector, which is sensitive mostly to events originating from the Southern hemisphere. From this period, 12 FRBs have been selected and no coincident neutrino candidate was observed. Upper limits on the per burst neutrino fluence have been derived using a power law spectrum, $\rm{\frac{dN}{dE_\nu}\propto E_\nu^{-\gamma}}$, for the incoming neutrino flux, assuming spectral indexes $\gamma$ = 1.0, 2.0, 2.5. Finally, the neutrino energy has been constrained by computing the total energy radiated in neutrinos assuming different distances for the FRBs. Constraints on the neutrino fluence and on the energy released are derived from the associated null results.

Quark deconfinement as a supernova explosion engine for massive blue supergiant stars

Blue-supergiant stars develop into core-collapse supernovae --- one of the most energetic outbursts in the universe --- when all nuclear burning fuel is exhausted in the stellar core. Previous attempts failed to explain observed explosions of such stars which have a zero-age main sequence mass of 50~M$_\odot$ or more. Here we exploit the largely uncertain state of matter at high density, and connect the modeling of such stellar explosions with a first-order phase transition from nuclear matter to the quark-gluon plasma. The resulting energetic supernova explosions can account for a large variety of lightcurves, from peculiar type II to super-luminous events. The remnants are neutron stars with quark matter core, known as hybrid stars, of about 2~M$_\odot$ at birth. A galactic event of this kind could be observable due to the release of a second neutrino burst. Its observation would confirm such a first-order phase transition at densities relevant for astrophysics.

Hypercritical accretion scenario in central compact objects accompanied with an expected neutrino burst

The measurement of the period and period derivative, and the canonical model of dipole radiation have provided a method to estimate the low superficial magnetic fields in the so-called Central Compact Objects (CCOs). In the present work, a scenario is introduced in order to explain the magnetic behavior of such CCOs. Based on magnetohydrodynamic simulations of the post core-collapse supernova phase during the hypercritical accretion episode, we argue that the magnetic field of a newborn neutron star could have been early buried. During this phase, thermal neutrinos are created mainly by the pair annihilation, plasmon decay, photo-neutrino emission and other processes. We study the dynamics of these neutrinos in this environment and also estimate the number expected of the neutrino events with their flavor ratios on Earth. The neutrino burst is the only viable observable that could provide compelling evidence of the hypercritical phase and therefore, the hidden magnetic field mechanism as the most favorable scenario to explain the anomalous low magnetic fields estimated for CCOs.