Abstract:
In connection with the recent suggestion by Tsytovich et al. that opacity in the solar core could be overestimated, we consider the following questions: i) What would a 10\% opacity reduction imply for the solar neutrino puzzle? ii) Is there any hope of solving the solar neutrino puzzle by changing opacity? iii) Is a 10\% opacity reduction testable with helioseismological data?

Abstract:
We extract information on the fluxes of Be and CNO neutrinos directly from solar neutrino experiments, with minimal assumptions about solar models. Next we compare these results with solar models, both standard and non standard ones. Finally we discuss the expectations for Borexino, both in the case of standard and non standard neutrinos.

Abstract:
We study the deuteron electrodisintegration with inclusion of the neutral currents focusing on the helicity asymmetry of the exclusive cross section in coplanar geometry. We stress that a measurement of this asymmetry in the quasi elastic region is of interest for an experimental determination of the weak form factors of the nucleon, allowing one to obtain the parity violating electron neutron asymmetry. Numerically, we consider the reaction at low momentum transfer and discuss the sensitivity of the helicity asymmetry to the strangeness radius and magnetic moment. The problems coming from the finite angular acceptance of the spectrometers are also considered.

Abstract:
This question, which often comes in when discussing solar neutrinos, is not clearly analysed in any textbook, to our knowledge. In this note we give a simple estimate of the flow time, also reminding its (ir)relevance to the solar neutrino problem.

Abstract:
We review the observational information on the constancy of the fine structure constant alpha. We find that small improvements on the measurement of ^{187}Re lifetime can provide significant progress in exploring the range of variability suggested by QSO data. We also discuss the effects of a time varying alpha on stellar structure and evolution. We find that radioactive dating of ancient stars can offer a new observational window.

Abstract:
We review recent advances concerning helioseismology, solar models and solar neutrinos. Particularly we shall address the following points: i) helioseismic tests of recent SSMs; ii)the accuracy of the helioseismic determination of the sound speed near the solar center; iii)predictions of neutrino fluxes based on helioseismology, (almost) independent of SSMs; iv)helioseismic tests of exotic solar models.

Abstract:
We summarize the results of solar neutrino experiments and update a solar model independent analysis of solar neutrino data. We discuss the implications of helioseismology on solar models and predicted solar neutrino fluxes. Finally , we discuss the potential of new experiments for detecting specific signatures of the proposed solutions to the solar neutrino puzzle.

Abstract:
By combining the results of SNO and Super-Kamiokande one can derive - in the absence of sterile neutrinos - the total neutrino flux produced from $^8$B decay in the Sun. We use this information to check the accuracy of several input parameters of solar model calculations. Opacity and p-p fusion cross section are constrained by the $^8$B flux measurement to the level of few per cent. The central solar temperature is determined to the one-percent level. We also find an upper limit for the flux on Earth of sterile neutrinos. We discuss the role of nuclear physics uncertainties on these determinations.

Abstract:
We present a new approach to study the properties of the sun. We consider small variations of the physical and chemical properties of the sun with respect to Standard Solar Model predictions and we linearize the structure equations to relate them to the properties of the solar plasma. By assuming that the (variation of) the present solar composition can be estimated from the (variation of) the nuclear reaction rates and elemental diffusion efficiency in the present sun, we obtain a linear system of ordinary differential equations which can be used to calculate the response of the sun to an arbitrary modification of the input parameters (opacity, cross sections, etc.). This new approach is intended to be a complement to the traditional methods for solar model calculation and allows to investigate in a more efficient and transparent way the role of parameters and assumptions in solar model construction. We verify that these Linear Solar Models recover the predictions of the traditional solar models with an high level of accuracy.

Abstract:
We consider a wide class of solar models with mixed core. Most of these models can be excluded as the predicted sound speed profile is in sharp disagreement with helioseismic constraints. All the remaining models predict $^7$Be and/or $^7$B neutrino fluxes at least as large as those of SSMs. In conclusion, helioseismology shows that a mixed solar core cannot account for the neutrino deficit implied by the current solar neutrino experiments.