Solar neutrinos: beyond standard solar models

Abstract

After a short survey of the physics of solar neutrinos, giving an overview of hydrogen burning reactions, predictions of standard solar models and results of solar neutrino experiments, we discuss the solar-model-independent indications in favour of non-standard neutrino properties. The experimental results look to be in contradiction with each other, even disregarding some experiment: unless electron neutrinos disappear in their trip from the sun to the earth, the fluxes of intermediate energy neutrinos (those from 7 Be electron capture and from the CNO cycle) result to be unphysically negative, or anyway extremely reduced with respect to standard solar model predictions. Next we review extensively non-standard solar models built as attempts to solve the solar neutrino puzzle. The dependence of the central solar temperature on chemical composition, opacity, age and on the values of the astrophysical S-factors for hydrogen-burning reactions is carefully investigated. Also, possible modifications of the branching among the various pp-chains in view of nuclear physics uncertainties are examined. Assuming standard neutrinos, all solar models examined fail in reconciling theory with experiments, even when the physical and chemical inputs are radically changed with respect to present knowledge and even if some of the experimental results are discarded.

What have we learnt about the Sun from the measurement of the 8B neutrino flux?

“…They are in good agreement with the values calculated (neglecting diffusion) in [6] (see table II) and in [7].…”

The Pisa Stellar Evolution Data Base for low-mass stars

“…A detailed discussion of the influence of the helium and metal microscopic diffusion on evolutionary properties can be found in Castellani & Degl'Innocenti (1999;see also Straniero et al 1997;Castellani et al 1997). Here we only recall that including microscopic diffusion at a fixed age reduces the TO luminosity by Δ log L/L ≈ 0.06; moreover, He is ignited within a slightly larger He core with a lower He abundance in the envelope, so that the ZAHB luminosity (in the RR Lyrae region at about log T eff = 3.83) is slightly decreased, while the TRGB luminosity is almost unaffected (see also Cassisi et al 1998).…”

Science and technology of Borexino: a real-time detector for low energy solar neutrinos

“…The signal rates at low and high energies are thus internally inconsistent with the sequential logic of energy production in the Sun, with or without invoking modification of the SSM. 14,15,16 This is referred to as the 7 Be-8 B problem.…”

“…Thus, activities with lifetimes shorter than this range can be vetoed by the muon detector. The absence of isotopes heavier than 12,13 C (and some 16,17,18 O in the fluor) is a key factor that limits the list of possible activities. A fundamental datum is the CTF result of ≈0.3 neutrons/ton,d correlated with muons, that sets a limiting rate on all possible spallation reactions.…”