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。     

Evidence for solar neutrino flux variability and its implications

Although KamLAND apparently rules out resonant-spin-flavor-precession (RSFP) as an explanation of the solar neutrino deficit, the solar neutrino fluxes in the Cl and Ga experiments appear to vary with solar rotation. Added to this evidence, summarized here, a power spectrum analysis of the Super-Kamiokande data reveals significant variation in the flux matching a dominant rotation rate observed in the solar magnetic field in the same time period. Three frequency peaks, all related to this rotation rate, can be explained quantitatively. A Super-Kamiokande paper reported no time variation of the flux, but showed the same peaks, there interpreted as statistically insignificant, due to an inappropriate analysis. This modulation is small (7%) in the Super-Kamiokande energy region (and below the sensitivity of the Super-Kamiokande analysis) and is consistent with RSFP as a subdominant neutrino process in the convection zone. The data display effects that correspond to solar-cycle changes in the magnetic field, typical of the convection zone. This subdominant process requires new physics: a large neutrino transition magnetic moment and a light sterile neutrino, since an effect of this amplitude occurring in the convection zone cannot be achieved with the three known neutrinos. It does, however, resolve current problems in providing fits to all experimental estimates of the mean neutrino flux, and is compatible with the extensive evidence for solar neutrino flux variability.     

The provenance and evolution of comets

The process of comet formation through the hierarchical aggregation of originally submicron-sized interstellar grains to form micron-sized particles and then larger bodies in the protoplanetary disc, culminating in the formation of planetesimals in the disc extending from Jupiter to beyond Neptune, is briefly reviewed. The planetesimal theory for the origin of comets implies the existence of distinct cometary reservoirs, with implications for the immediate provenance of observed comets (both long-period and short-period) and their evolution as a result of planetary perturbations and physical decay, for example splitting and sublimation. The principal mode of cometary decay and collisional interaction with the terrestrial planets is through the formation and evolution of streams of cometary debris and hitherto undiscovered families of cometary asteroids. Recent dynamical results, in particular the sungrazing and sun-colliding end-state for short-period comet and asteroid orbits, are briefly discussed.     

Thermo-acoustic sound generation in the interaction of pulsed proton and laser beams with a water target

The generation of hydrodynamic radiation in interactions of pulsed proton and laser beams with matter is explored. The beams were directed into a water target and the resulting acoustic signals were recorded with pressure sensitive sensors. Measurements were performed with varying pulse energies, sensor positions, beam diameters and temperatures. The obtained data are matched by simulation results based on the thermo-acoustic model with uncertainties at a level of 10%. The results imply that the primary mechanism for sound generation by the energy deposition of particles propagating in water is the local heating of the medium. The heating results in a fast expansion or contraction and a pressure pulse of bipolar shape is emitted into the surrounding medium. An interesting, widely discussed application of this effect could be the detection of ultra-high energetic cosmic neutrinos in future large-scale acoustic neutrino detectors. For this application a validation of the sound generation mechanism to high accuracy, as achieved with the experiments discussed in this article, is of high importance.     

Probing the Earth’s Interior with the LENA Detector

A future large-volume liquid scintillator detector such as the proposed 50 kton LENA (Low Energy Neutrino Astronomy) detector would provide a high-statistics measurement of terrestrial antineutrinos originating from β-decays of the uranium and thorium chains. Additionally, the neutron is scattered in the forward direction in the detection reaction . Henceforth, we investigate to what extent LENA can distinguish between certain geophysical models on the basis of the angular dependence of the geoneutrino flux. Our analysis is based on a Monte-Carlo simulation with different levels of light yield, considering an unloaded PXE scintillator. We find that LENA is able to detect deviations from isotropy of the geoneutrino flux with high significance. However, if only the directional information is used, the time required to distinguish between different geophysical models is of the order of severals decades. Nonetheless, a high-statistics measurement of the total geoneutrino flux and its spectrum still provides an extremely useful glance at the Earth’s interior.     

On the origin of transient effects in the solar neutrino experiment

Correlation studies of the pattern of time variation of the recorded solar neutrino flux monitored through the reaction Cl³⁷ → Ar³⁷ with various parameters of solar activity is suggestive of possible emission of a penetrating neutral particle from the sun influencing directly or indirectly the transformation Cl³⁷ → Ar³⁷ deep underground at the required rates. This possibility has to be invoked in view of the difficulties in generating the observed pattern of variations through a large modulatory mechanism involving the electron neutrino. The prediction that follows is the possible existence of a time varying component (diurnal) in the rate of some nuclear transmutations deep underground caused by an unknown neutral radiation having an interaction cross section with matter probably much larger than the canonical value of 10^-36 cm² per nucleon speculated upon by some authors in the WIMP scenario for the sun.     

The LMC supernova (SN 1987 A) as a probe for the outcome of stellar collapse

Implications from the available information on the supernova SN 1987 A are discussed for the supernova models. We derive an upper bound of 10–25 eV for the neutrino rest mass.     

The Neutrino Telescope Antares

Whilst the number of observed astrophysical sources of γ-rays is now moderately high, only three astrophysical objects have been studied with neutrinos, namely the Sun, a supernova (SN1987A) and the Earth (its atmosphere). However, astro-neutrinos may give a new boost to astrophysics, similar to the impressive progress provided during the last decades by γ-rays. The ANTARES collaboration aims to build a large neutrino telescope under the Mediterranean Sea at a depth of 2500 m. To reach this goal, a remarkable effort of R&D has been performed in recent years that has culminated in the deployment, connection and operation of two prototype strings. The final detector will be composed of 12 strings and will be ready by 2007.     

Acoustic and optical variations during rapid downward motion episodes in the deep north-western Mediterranean Sea

An Acoustic Doppler Current Profiler (ADCP) was moored at the deep-sea site of the ANTARES neutrino telescope near Toulon, France, thus providing a unique opportunity to compare high-resolution acoustic and optical observations between 70 and 170 m above the sea bed at 2475 m. The ADCP measured downward vertical currents of magnitudes up to 0.03 m s⁻¹ in late winter and early spring 2006. In the same period, observations were made of enhanced levels of acoustic reflection, interpreted as suspended particles including zooplankton, by a factor of about 10 and of horizontal currents reaching 0.35 m s⁻¹. These observations coincided with high light levels detected by the telescope, interpreted as increased bioluminescence. During winter 2006 deep dense-water formation occurred in the Ligurian subbasin, thus providing a possible explanation for these observations. However, the 10-20 days quasi-periodic episodes of high levels of acoustic reflection, light and large vertical currents continuing into the summer are not direct evidence of this process. It is hypothesized that the main process allowing for suspended material to be moved vertically later in the year is local advection, linked with topographic boundary current instabilities along the rim of the ‘Northern Current’.