A model independent approach to future solar neutrino experiments

We discuss here what model independent information about properties of neutrinos and of the sun can be obtained from future solar neutrino experiments (SNO, Super-Kamiokande). It is shown that in the general case of transitions of solar ν_e's into νμ and/or ντ the initial ⁸B neutrino flux can be measured by the observation of NC events. From the CC measurements the ν_e survival probability can be determined as a function of neutrino energy. The general case of transitions of solar ν_e's into active as well as sterile neutrinos is considered. A number of relations between measurable quantities the test of which will allow to answer the question whether there are sterile neutrinos in the solar neutrino flux on the earth are derived. Transitions of solar ν_e's into active and sterile states due to neutrino mixing and Dirac magnetic moments or into active left-handed neutrinos and active right-handed antineutrinos due to neutrino mixing and Majorana transition magnetic moments are also considered. It is shown that future solar neutrino experiments will allow to distinguish between the cases of Dirac and Majorana magnetic moments.     

The ANTARES telescope neutrino alert system

The ANTARES telescope has the capability to detect neutrinos produced in astrophysical transient sources. Potential sources include gamma-ray bursts, core collapse supernovae, and flaring active galactic nuclei. To enhance the sensitivity of ANTARES to such sources, a new detection method based on coincident observations of neutrinos and optical signals has been developed. A fast online muon track reconstruction is used to trigger a network of small automatic optical telescopes. Such alerts are generated for special events, such as two or more neutrinos, coincident in time and direction, or single neutrinos of very high energy.     

Astrophysical interpretation of small-scale neutrino angular correlation searches with IceCube

The IceCube Neutrino Observatory has discovered a diffuse all-flavor flux of high-energy astrophysical neutrinos. However, the corresponding astrophysical sources have not yet been identified. Neither significant point sources nor significant angular correlations of event directions have been observed by IceCube or other instruments to date. We present a new method to interpret the non-observation of angular correlations in terms of exclusions on the strength and number of point-like neutrino sources in generic astrophysical scenarios. Additionally, we constrain the presence of these sources taking into account the measurement of the diffuse high-energy neutrino flux by IceCube. We apply the method to two types of astrophysically motivated source count distributions: The first type is obtained by considering the cosmological evolution of the co-moving density of active galaxies, while the second type is directly derived from the gamma ray source count distribution observed by Fermi-LAT. As a result, we constrain the possible parameter space for both types of source count distributions.     

Detection of Solar Neutrinos

The present status of solar neutrino detection is reviewed. Results from the Homestake, Kamiokande, Super-Kamiokande, GALLEX and SAGE detectors all show a deficit when compared to recent standard solar model calculations. Two of these detectors, GALLEX and SAGE, have recently been checked with artificial 51Cr neutrino sources. It is shown that astrophysical scenarios to solve the solar neutrino problems are not favoured by the data. There is hope that the results of Super-Kamiokande and the forthcoming solar neutrino experiments can provide the answers to the open questions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhancement of the sterile neutrino yield at high density and increasing neutronization of matter

The relative yields of active and sterile neutrinos in matter with a high density and different degrees of neutronization have been calculated. A significant increase in the proportion of sterile neutrinos produced in superdense matter when the degree of neutronization approaches two has been found. The results obtained can be used to calculate the neutrino fluxes for matter with a high density and different degrees of neutronization in astrophysical processes, for example, the formation of a protoneutron supernova core.     

Methods for point source analysis in high energy neutrino telescopes

Neutrino telescopes are moving steadily toward the goal of detecting astrophysical neutrinos from the most powerful galactic and extragalactic sources. Here we describe analysis methods to search for high energy point-like neutrino sources using detectors deep in the ice or sea. We simulate an ideal cubic kilometer detector based on real world performance of existing detectors such as AMANDA, IceCube, and ANTARES. An unbinned likelihood ratio method is applied, making use of the point spread function and energy distribution of simulated neutrino signal events to separate them from the background of atmospheric neutrinos produced by cosmic ray showers. The unbinned point source analyses are shown to perform better than binned searches and, depending on the source spectral index, the use of energy information is shown to improve discovery potential by almost a factor of two.     

Radio Cherenkov signals from the Moon: Neutrinos and cosmic rays

Neutrino production of radio Cherenkov signals in the Moon is the object of radio telescope observations. Depending on the energy range and detection parameters, the dominant contribution to the neutrino signal may come from interactions of the neutrino on the Moon facing the telescope, rather than neutrinos that have traversed a portion of the Moon. Using the approximate analytic expression of the effective lunar aperture from a recent paper by Gayley, Mutel and Jaeger, we evaluate the background from cosmic ray interactions in the lunar regolith. We also consider the modifications to the effective lunar aperture from generic non-standard model neutrino interactions. A background to neutrino signals are radio Cherenkov signals from cosmic ray interactions. For cosmogenic neutrino fluxes, neutrino signals will be difficult to observe because of low neutrino flux at the high energy end and large cosmic ray background in the lower energy range considered here. We show that lunar radio detection of neutrino interactions is best suited to constrain or measure neutrinos from astrophysical sources and probe non-standard neutrino-nucleon interactions such as microscopic black hole production.     

GRBs on probation: Testing the UHE CR paradigm with IceCube

Gamma ray burst (GRB) fireballs provide one of very few astrophysical environments where one can contemplate the acceleration of cosmic rays to energies that exceed 10²⁰ eV. The assumption that GRBs are the sources of the observed cosmic rays generates a calculable flux of neutrinos produced when the protons interact with fireball photons. With data taken during construction IceCube has already reached a sensitivity to observe neutrinos produced in temporal coincidence with individual GRBs provided that they are the sources of the observed extra-galactic cosmic rays. We here point out that the GRB origin of cosmic rays is also challenged by the IceCube upper limit on a possible diffuse flux of cosmic neutrinos which should not be exceeded by the flux produced by all GRB over Hubble time. Our alternative approach has the advantage of directly relating the diffuse flux produced by all GRBs to measurements of the cosmic ray flux. It also generates both the neutrino flux produced by the sources and the associated cosmogenic neutrino flux in a synergetic way.     

Exact analysis of the combined data of SNO and Super-Kamiokande

Comparison of solar-neutrino signals in SNO [Phys. Rev. Lett. 87 (2001) 071301] and Super-Kamiokande (SK) [Phys. Rev. Lett. 86 (2001) 5651] detectors results in discovery of ν_e→ν_μ,τ oscillations at level 3.1–3.3σ [Phys. Rev. Lett. 87 (2001) 071301]. This comparison involves the assumption of neutrino spectrum and a choice for the thresholds of detection in both experiments. In this paper we obtain an exact formula for the comparison of the signals which is valid for arbitrary spectra and thresholds. We find that the no-oscillation hypothesis (astrophysical solutions) is excluded at 3.3σ. If the energy-dependent component of the survival probability for electron neutrinos is small as compared with the average value, i.e. in the case of small distortion of the observed spectrum, the oscillation hypothesis can also be tested to similar accuracy. The oscillation to sterile neutrino only, is excluded at 3.3σ level, and oscillation to active neutrinos is confirmed at 2.8σ.     

Stopping power of matter and energy losses of solar neutrinos

The effects of neutrino mass and oscillations are investigated in the calculations of energy losses of solar neutrinos. In these calculations, we take into account the full energy dependence of the stopping power of matter for neutrinos. The case of Majorana neutrinos are also investigated. It is found that the total losses of energy of solar neutrinos are too small to account for the solar neutrino problem.     

Method to calculate the neutrino flux from a resolved source of high energy gamma-rays: the case of SNR RX J1713.7-3946

In this paper we show how to calculate the neutrino flux from a resolved source of high energy gamma-rays, of which have been measured fluxes and spectral indexes of each of the parts in which has been divided for the observations. For the calculation of the neutrino flux need to know the theoretical photon/neutrino ratios and have to consider the oscillation probability of neutrinos. As a numerical example the case of the Supernova Remnant RX J1713.7-3946 observed by H.E.S.S. experiment is presented here. Gamma-rays up to tens of TeV have been observed from RX J1713.7-3946, making this source a possible site of hadronic interactions and thus a source of neutrinos. The H.E.S.S. experiment observed 14 different regions in RX J1713.7-3946, measuring in each one the gamma-ray flux and spectral index. The technique presented in this paper can be applied to other high energy astrophysical sources, point-like or resolved.     

太阳中微子"亏缺"与非标准太阳模型

系统阐述了太阳中微子“亏缺”问题出现的背景,包括介绍标准太阳模型,太阳内部的相聚变反应,太阳中微子能谱和流量的理论估算,以及太阳中微子探测实验和结果。讨论了为解释太阳中微子“亏缺”而提出的各种非标准太阳模型以及近年来愈益受到重视的中微子振动问题。     

Constraints on ultracompact minihalos using neutrino signals from gravitino dark matter decay

Ultracompact dark matter minihalos(UCMHs) would be formed during the early universe if there were large density perturbations.If dark matter can decay into particles described by the standard model,such as neutrinos,these objects would become potential astrophysical sources of emission which could be detected by instruments such as IceCube.In this paper,we investigate neutrino signals from nearby UCMHs due to gravitino dark matter decay and compare these signals with the background neutrino flux which is mainly from the atmosphere to obtain constraints on the abundance of UCMHs.     

Pionic photons and neutrinos from cosmic ray accelerators

Identifying the accelerators that produce the Galactic and extragalactic cosmic rays has been a priority mission of several generations of high energy gamma ray and neutrino telescopes; success has been elusive so far. Detecting the gamma-ray and neutrino fluxes associated with cosmic rays reaches a new watershed with the completion of IceCube, the first neutrino detector with sensitivity to the anticipated fluxes, and the construction of CTA, a ground-based gamma ray detector that will map and study candidate sources with unprecedented precision. In this paper, we revisit the prospects for revealing the sources of the cosmic rays by a multiwavelength approach; after reviewing the methods, we discuss supernova remnants, gamma ray bursts, active galaxies and GZK neutrinos in some detail.     

History of neutrino telescope/astronomy

Neutrinos represent a new window to the Universe. In this paper we discuss the attempts to detect neutrinos, starting with the Homestake experiment, which showed the deficit of solar neutrinos. The detection of neutrinos from SN 1987A gave a new impetus to neutrino research. By using successive generations of neutrino detectors it was possible to show that the solar neutrino deficit could be explained by a flavor change of massive neutrinos. With the latest detector, kamLAND, it is possible to investigate the interior of the Earth through the detection of geoneutrinos.     

Neutrino spin-flavor oscillations in solar environment

We study the phenomenon of neutrino spin-flavor oscillations due to solar magnetic fields. This allows us to examine how significantly the electron neutrinos produced in the solar interior undergo a resonant spin-flavor conversion. We construct analytical models for the solar magnetic field in all the three regions of the Sun. Neutrino spin-flavor oscillations in this magnetic field are examined by studying the level crossing phenomenon and comparing the two cases of zero and non-zero vacuum mixing respectively.Results from the Borexino experiment are used to place an upper limit on the magnetic field in the solar core. Related phenomena such as effects of matter on neutrino spin transitions and differences between Dirac and Majorana transitions in the solar magnetic fields are also discussed.     

Detecting extra-galactic supernova neutrinos in the Antarctic ice

Building on the technological success of the IceCube neutrino telescope, we outline a prospective low-energy extension that utilizes the clear ice of the South Pole. Aiming at a 10 Mton effective volume and a 10 MeV threshold, the detector would provide sufficient sensitivity to detect neutrino bursts from core-collapse supernovae (SNe) in nearby galaxies. The detector geometry and required density of instrumentation are discussed along with the requirements to control the various sources of background, such as solar neutrinos. In particular, the suppression of spallation events induced by atmospheric muons poses a challenge that will need to be addressed. Assuming this background can be controlled, we find that the resulting detector will be able to detect SNe from beyond 10 Mpc, delivering between 10 and 41 regular core-collapse SN detections per decade. It would further allow to study more speculative phenomena, such as optically dark (failed) SNe, where the collapse proceeds directly to a black hole, at a detection rate similar to that of regular SNe. We find that the biggest technological challenge lies in the required number of large area photo-sensors, with simultaneous strict limits on the allowed noise rates. If both can be realized, the detector concept we present will reach the required sensitivity with a comparatively small construction effort and hence offers a route to future routine observations of SNe with neutrinos.     

On the observability of high-energy neutrinos from gamma ray bursts

A method is presented for the identification of high-energy neutrinos from gamma ray bursts (GRBs) by means of a large-scale neutrino telescope. The procedure makes use of a time profile stacking technique of observed neutrino induced signals in correlation with satellite observations. By selecting a rather wide time window, a possible difference between the arrival times of the gamma and neutrino signals may also be identified. This might provide insight in the particle production processes at the source. By means of a toy model it will be demonstrated that a statistically significant signal can be obtained with a km³ scale neutrino telescope on a sample of 500 GRBs for a signal rate as low as 1 detectable neutrino for 3% of the bursts.     

A heuristic remark on the periodic variation in the number of solar neutrinos detected on Earth

Four operating neutrino observatories confirm the long standing discrepancy between detected and predicted solar neutrino flux. Among these four experiments the Homestake experiment is taking data for almost 25 years. The reliability of the radiochemical method for detecting solar neutrinos has been tested recently by the GALLEX experiment. All efforts to solve the solar neutrino problem by improving solar, nuclear, and neutrino physics have failed so far. This may also mean that the average solar neutrino flux extracted from the four experiments may not be the proper quantity to explain the production of neutrinos in the deep interior of the Sun. Occasionally it has been emphasized that the solar neutrino flux may vary over time. In this paper we do address relations among specific neutrino fluxes produced in the proton-proton chain that are imposed by the coupled systems of nonlinear partial differential equations of solar structure and kinetic equations by focusing our attention on a statistical interpretation of selected kinetic equations of PPII/PPIII branch reactions of the protonproton chain. A fresh look at the statistical implications for the outcome of kinetic equations for nuclear reactions may shed light on recent claims that the⁷ Be-neutrino flux of the Sun is suppressed in comparison to the pp- and⁸B neutrino fluxes and may hint at that the solar neutrino flux is indeed varying over time as shown by the Homestake experiment.     

Galactic PeV neutrinos

The IceCube experiment has detected two neutrinos with energies between 1 and 10 PeV. They might have originated from Galactic or extragalactic sources of cosmic rays. In the present work we consider hadronic interactions of the diffuse very high energy cosmic rays with the interstellar matter within our Galaxy to explain the PeV neutrino events detected in IceCube. We also expect PeV gamma ray events along with the PeV neutrino events if the observed PeV neutrinos were produced within our Galaxy in hadronic interactions. PeV gamma rays are unlikely to reach us from sources outside our Galaxy due to pair production with cosmic background radiation fields. We suggest that in future with simultaneous detections of PeV gamma rays and neutrinos it would be possible to distinguish between Galactic and extragalactic origins of very high energy neutrinos.