Abstract
The neutrino flux at Earth is dominated in the keV energy range by the neutrinos produced in the Sun through thermal processes, namely photo production, bremsstrahlung, plasmon decay, and emission in free-bound and bound-bound transitions of partially ionized elements heavier than hydrogen and helium. Such a component of the neutrino flux is conspicuously absent from popular analyses of the all-sources spectrum at Earth, whereas if detected it could be a source of information about solar physics. Moreover, it would be the relevant background for keV-mass sterile neutrino dark matter direct searches.
Highlights
How to compute the thermal neutrino fluxABCD processes Low-energy neutrinos are produced in the solar plasma by pair-production processes, where nonrelativistic electrons, whose velocities and spins are coupled to the ambient electromagnetic fields, are the sources for neutrino pair emission
Our analysis improves the only detailed previous calculation of the thermal flux [6] in different regards
Such a component of the neutrino flux is conspicuously absent from popular analyses of the all-sources spectrum at Earth, whereas if detected it could be a source of information about solar physics
Summary
ABCD processes Low-energy neutrinos are produced in the solar plasma by pair-production processes, where nonrelativistic electrons, whose velocities and spins are coupled to the ambient electromagnetic fields, are the sources for neutrino pair emission. Note that the delta function does not depend on the momentum transfer, because the mass of the ions turns out to be much bigger than other energy scales; this is known as “long wavelength approximation” The latter allows us to express the neutrino pair emission rate of equation (3) factorizing the term related to emitted radiation (the neutrino pairs) from the term describing the medium (thermal electrons interacting with nuclei). We have calculated the free-bound and bound-bound contribution exploiting the relation between neutrino pair emissivity and photon opacity. This relation is straightforwardly obtained in the Bremsstrahlung case, where dnγ dω
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