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تسجيل مستخدم جديدSolar neutrinos (almost) without standard solar models
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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.
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Recent solar neutrino results together with the assumption of a stationary Sun imply severe constraints on the individual components of the total neutrino flux : $Phi_{Be} leq 0.7 cdot 10^{9} cm^{-2} s^{-1}, Phi_{CNO} leq 0.6 cdot 10^{9} cm^{-2} s^{-
1}$ and $64 cdot 10^{9} cm^{-2} s^{-1} leq Phi_{pp+pep} leq 65 cdot 10^{9} cm^{-2} s^{-1}$ (at 1$ sigma$ level), the constraint on $ u_{Be}$ being in strong disagreement with $Phi_{Be}^{SSM} = 5 cdot 10^{9} cm^{-2} s^{-1}$. We study a large variety of non-standard solar models with low inner temperatures, finding that the temperature profiles T(m) follow the homology relationship: T(m)=k$T(m)^{SSM}$, so that they are specified just by the central temperature $T_{c}$. There is no value of $T_{c}$ which can account for all the available experimental results and also if we restrict to consider just Gallium and Kamiokande results the fit is poor. Finally we discuss what can be learned from new generation experiments, planned for the detection of monochromatic solar neutrinos, about the properties of neutrinos and of the Sun.
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 7Be 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.
Solar neutrino experiments have yet to see directly the transition region between matter-enhanced and vacuum oscillations. The transition region is particularly sensitive to models of non-standard neutrino interactions and propagation. We examine sev
eral such non-standard models, which predict a lower-energy transition region and a flatter survival probability for the ^{8}B solar neutrinos than the standard large-mixing angle (LMA) model. We find that while some of the non-standard models provide a better fit to the solar neutrino data set, the large measured value of theta_{13} and the size of the experimental uncertainties lead to a low statistical significance for these fits. We have also examined whether simple changes to the solar density profile can lead to a flatter ^{8}B survival probability than the LMA prediction, but find that this is not the case for reasonable changes. We conclude that the data in this critical region is still too poor to determine whether any of these models, or LMA, is the best description of the data.
It has been speculated that quantum gravity might induce a foamy space-time structure at small scales, randomly perturbing the propagation phases of free-streaming particles (such as kaons, neutrons, or neutrinos). Particle interferometry might then
reveal non-standard decoherence effects, in addition to standard ones (due to, e.g., finite source size and detector resolution.) In this work we discuss the phenomenology of such non-standard effects in the propagation of electron neutrinos in the Sun and in the long-baseline reactor experiment KamLAND, which jointly provide us with the best available probes of decoherence at neutrino energies E ~ few MeV. In the solar neutrino case, by means of a perturbative approach, decoherence is shown to modify the standard (adiabatic) propagation in matter through a calculable damping factor. By assuming a power-law dependence of decoherence effects in the energy domain (E^n with n = 0,+/-1,+/-2), theoretical predictions for two-family neutrino mixing are compared with the data and discussed. We find that neither solar nor KamLAND data show evidence in favor of non-standard decoherence effects, whose characteristic parameter gamma_0 can thus be significantly constrained. In the Lorentz-invariant case n=-1, we obtain the upper limit gamma_0<0.78 x 10^-26 GeV at 95% C.L. In the specific case n=-2, the constraints can also be interpreted as bounds on possible matter density fluctuations in the Sun, which we improve by a factor of ~ 2 with respect to previous analyses.
Most neutrino mass extensions of the standard electroweak model entail non-standard interactions which, in the low energy limit, can be parametrized in term of effective four-fermion operators $ u_alpha u_beta bar f f $. Typically of sub-weak streng
th, $epsilon_{alpha beta} G_F$, these are characterized by dimensionless coupling parameters, $epsilon_{alpha beta}$, which may be relatively sizeable in a wide class of schemes. Here we focus on non-universal (NU) flavor conserving couplings ($alpha = beta$) with electrons ($f = e$) and analyse their impact on the phenomenology of solar neutrinos. We consistently take into account their effect both at the level of propagation where they modify the standard MSW behavior, and at the level of detection, where they affect the cross section of neutrino elastic scattering on electrons. We find limits which are comparable to other existing model-independent constraints.
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