Time variations of the solar neutrino flux

The Fourier analysis of the argon-37 production rate for runs 18–80 observed in Davis's well-known solar neutrino experiment is presented. The method of Fourier analysis with the unequally-spaced data of Davis and associates is described and the discovered periods are compared with recently published results for the analysis of the data of runs 18–69. The harmonic analysis of the data of runs 18–80 shows time variations of the solar neutrino flux with periods =8.33, 5.26, 2.13, 1.56, 0.83, 0.64, 0.54, and 0.50 yr, respectively, which confirms earlier computations.     

Effect of Coulomb collisions on time variations of the solar neutrino flux

We consider the processes that might suppress the time variations in the solar neutrino flux produced by the radial motion of the Earth through the neutrino interference pattern. We calculate these time variations and the extent to which they are suppressed by Coulomb collisions of the neutrino-emitting nuclei. This is done for both the 0.862-MeV ⁷Be neutrino line and the continuous neutrino spectrum, assuming a Gaussian energy response function of the neutrino detector. We find that the collisional decoherence averages out the time variations for neutrino masses A simple and clear physical picture of the time-dependent solar neutrino problem is presented and qualitative coherence criteria are discussed.     

Quasi-periodic variation in the solar neutrino flux revisited

Neutrino capture rate data from the Homestake chlorine experiment (1970–1990) has been spectrally analysed. The data were smoothed by a 4-month equally-spaced sequence and by a cubic spline polynomial approximation. Fourier (FFT), maximum entropy spectrum analysis (MESA), and power spectrum analysis (PSA) employing the Blackman-Tukey window were used. The significant periodicities obtained are: 1 ± 0.1, 1.4 ± 0.2, 2.4 ± 0.2, 5 ± 0.2, and 11 ± 1.5 years. A possible correlation with similar coincident periods in other solar-terrestrial phenomena is discussed.     

The magnitude distribution, perihelion distribution and flux of long-period comets

The mass distribution and perihelion distribution of long-period comets are re-assessed. The mass distribution index is found to be 1.598±0.016 , indicating that the distribution is somewhat steeper than was obtained by previous analyses of an amalgam of all the available historical data. The number of long-period comets that have orbital perihelion distances, q , that fall in a specific q to q +d q range is found to be independent of q . It is also noted that the flux of long-period comets to the inner Solar system has remained constant throughout recorded history.
The number of long-period comets, , per 1-au interval of perihelion distance, per year, brighter than H , entering the inner Solar system is found to be given by log₁₀ =−2.607+0.359 H . It is therefore estimated that, for example, about 0.5, 30 and 2000 long-period comets with absolute magnitudes brighter than 0, 5 and 10 respectively pass the Sun on orbits with perihelion distances less than 2.0 au, every century.     

On the proposed associations of solar neutrino flux with solar particles,cosmic rays,and the solar activity cycle

It has been proposed that the observed solar neutrino flux exhibits important correlations with solar particles, galactic cosmic rays, and the sunspot cycle, with the latter correlation being opposite in phase and lagging behind the sunspot cycle by about one year. Re-examination of the data-available interval 1971–1981, employing various tests of statistical significance, however, suggests that such a claim is, at present, unwarrantable. For example, on the associations of solar neutrino flux and cosmic-ray flux with the Ap geomagnetic index, neither were found to be statistically significant (at the 95% level of confidence), regardless of the choice of lag (-1, 0, or +1 yr). Presuming linear fits, all correlations with Ap had coefficients of determination (r ², where r is the linear correlation coefficient) less than 16%, meaning that 16% of the variation in the selected test parameters could be explained by the variation in Ap. Similarly, on the associations of solar neutrino flux and cosmic ray flux with sunspot number, only the latter association proved to be of statistical importance. Using the best linear fits, the correlation between yearly averages of solar neutrino flux and sunspot number had r ² 19%, the correlation between weighted moving averages (of order 5) of solar neutrino flux and sunspot number had r ² 45%, and the correlation between cosmic-ray flux and sunspot number had r ² 76%, all correlations being inverse associations. Solar neutrino flux was found not to correlate strongly with cosmic-ray flux, and the Ap geomagnetic index was found not to correlate strongly with sunspot number.     

On the solar neutrino puzzle

Based on the available solar neutrino and helioseismic data a possible astrophysical solution of the solar neutrino problem is proposed. Forthcoming high and low energy neutrino measurements and helioseismic experiments will allow one to check the considered possibility.     

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.     

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.     

Quasi-biennial periodicity in the solar neutrino flux and its relation to the solar structure

By analysing the observed results on the neutrino flux from the Sun for the years 1970–1978, it is shown that the production rate of the neutrinos at the central core of the Sun had been varying with a period almost equal to 26 months for these years. This so-called quasi-biennial periodicity in this rate suggests that the physical state of the central core of the Sun must have been modulated with this period through the variation of physical parameters as temperature and the chemical composition at the central core of the Sun. An idea to interpret this observed periodicity is thus proposed by taking the variations of these parameters into consideration. Some supporting evidence on this periodicity can be found on the variations of the solar activity as the relative sunspot numbers and the equatorial rotation speed of the Sun.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Active region evolution and solar flux variations

The goal of this study is to relate the changes in the solar radiative output to the growth and decay of magnetic active regions. We will test the assumption that each index of radiation variability is a convolution of an active-region magnetic driving function and a response function. The first step has been to identify the appropriate driving function. This driving function was assumed to have been data from the magnetic active regions derived from the Mount Wilson daily magnetograms (Howard, 1989). The daily magnetic reports were sorted to give active-region sequences. To estimate the magnetic flux of active regions outside the observing window, (i.e., behind the limb) we fit the data to a growing-and-decaying exponential function, which permits independent growth and decay. This double exponential gives reasonable fats to the observed temporal evolution of active-region magnetic flux.     

Solar neutrino flux,cosmic rays,and the solar activity cycle

It is suggested that the experimental data on the solar neutrino flux as measured by Davis and his collaborators from 1970 to 1982 vary with the solar activity cycle to a very high level of statistical significance for all the available tests of the hypothesis (e.g., (t-test, ²-test, run test, Wilcoxon-Mann-Whitney test) when the solar neutrino flux data are computed from the weighted moving averages of order 5. The above tests have also been applied to the data that have been generated by the Monte Carlo simulation with production rate and background rate parameters that are typical of those in the actual experiment. It is shown that the Monte Carlo simulated data do not indicate a variation within the solar cycle. Thus the moving average data strongly favours the variation within the solar activity cycle.     

Observations of quasiperiodic variations in the solar flux at 10.7 GHz

Observations of the continuum microwave flux at 2.8 cm from quiet regions of the solar disc reveal low amplitude, quasiperiodic fluctuations at periods of 234 s and 150 s. For oscillating elements 10 arc seconds in extent, the corresponding peak to peak temperature variations are 230 K and 190 K. The energy flux in the oscillations is estimated to be 2.5x10² ergs cm² s^–1, assuming they are caused by acoustic waves. If the oscillating elements are 1 arc second in extent, the energy flux is comparable to that required for coronal heating.No evidence is found for strong oscillations at periods greater than 250 s, although other authors have claimed microwave detection of strong fluctuations at periods of 280 s and 400 s.     

Atmospheric temperature response to solar cycle UV flux variations

A radiative-convective climate model was used to explore the response of the mean global vertical temperature structure to a variation in the solar UV flux over the solar cycle. The model predicted a cooling of the troposphere and a warming of the stratosphere from solar minimum to solar maximum. The response of the atmospheric temperature to solar UV variations was found to be moderated by a concomitant change in the mean global stratospheric ozone content.     

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.     

On the fourier spectrum analysis of the solar neutrino capture rate

Periodic variations in Davis' experimental data concerning the solar neutrino capture rate are derived on the basis of a Fourier spectrum analysis. Variations in the ³⁷Ar production rate are obtained for a series of randomly spaced observations in the period 1970–1985 (runs 18–89). The harmonic analysis of runs 18–89 has determined solar neutrino capture rate variations with periods of 8.33, 5.00, 2.13, 1.61, 0.83, 0.61, 0.54, and 0.51 yr, thereby confirming earlier calculations performed for the set of runs 18–69 (1983), 18–74 (1985a), and 18–80 (1985b). The results also confirm those of Sakurai (1979) who showed that there is strong evidence that the observed solar neutrino flux has a tendency to vary with quasi-biennial periodicity. We show that the results of the Fourier spectrum analysis do not depend upon certain high or low values in Davis' experimental data.     

An investigation on the relationship between solar irradiance signal from ERBS and 8B solar neutrino flux signals from SNO

In the present work an attempt has been made to investigate statistical association between solar neutrino flux data (both D₂O and Salt data) collected from Sudbury Neutrino Observatory and solar irradiance data detected by Earth Radiation Budget Satellite. To serve the present purpose we have used the Multifractal Detrended Cross Correlation Analysis (MF-DCCA) based on Detrended Fluctuation Analysis (MF-X-DFA) method and the Detrending Moving Average Analysis (MF-X-DMA) which explores the long term power-law cross correlations between above two pairs of data sets. Investigation also has been made to find the frequency and time dependent local phase relationship in each pair of data sets using continuous wavelet transform (CWT) based Semblance Analysis. The Semblance Analysis reveals that there exists positive phase correlation as well as negative phase correlation between solar irradiance and D₂O data at different time sub-intervals. This type of mixed phase correlation is also experienced between solar irradiance and Salt data at different time sub-intervals. The causal relationship between the D₂O and the solar irradiance time series and that between Salt and solar irradiance time series have been revealed using Singular Spectral Analysis (SSA). Calculations indicate that possibly the present solar neutrino flux data (both D₂O and Salt data) is supportive to predict the solar irradiance data but may not the vice versa which in turn suggests that the variability of nuclear energy generation process inside the Sun may influence the solar activity.     

On possible long-period pulsations in the hard X-ray flux of Cygnus X-1

Fourier analysis performed on the data of three balloon observations (20–200 keV) of Cygnus X-1 has shown a significant peak of the power spectral density at about 17 s. Possible periodic pulsations, sustained over periods of at least one hour, could be responsible for the peak we detected. Results of computer simulations in terms of a superposition of randomly occurring pulses give some support to this interpretation.Paper presented at the COSPAR Symposium on Fast Transients in X-and Gamma-Rays, held in Varna, Bulgaria, May 1975.     

Solar neutrino and solar particles

Examination of the most recent data on solar neutrino shows that there is a statistically significant relationship between solar neutrino and solar particles.     

Chemistry of the solar neutrino experiment

The possibility of chemical ‘trapping’ of the Ar⁺ ion in the reaction $$v{\text{ }} + {\text{ }}^{{\text{37}}} {\text{Cl}} \to {\text{ }}^{{\text{37}}} {\text{Ar}}^{\text{ + }} + {\text{ e}}^ - ,$$ when it takes place in tetrachloroethylene (C₂Cl₄) liquid, is examined in detail. It is concluded that if trapping does take place, the rate is much smaller than the charge neutralization rate. Therefore, this niechanism cannot explain the observed small rate of Ar production in the Brookhaven solar neutrino experiment. A detailed examination of a number of experiments which are sensitive to possible trapping lends strong support to this conclusion.