Solar neutrino flux at keV energies

Abstract

We calculate the solar neutrino and antineutrino flux in the keV energy range. The dominant thermal source processes are photoproduction ($\gamma e\to e\nu \bar{\nu }$), bremsstrahlung ($e+Ze\to Ze+e+\nu \bar{\nu }$), plasmon decay ($\gamma \to \nu \bar{\nu }$), and $\nu \bar{\nu }$ emission in free-bound and bound-bound transitions of partially ionized elements heavier than hydrogen and helium. These latter processes dominate in the energy range of a few keV and thus carry information about the solar metallicity. To calculate their rate we use libraries of monochromatic photon radiative opacities in analogy to a previous calculation of solar axion emission. Our overall flux spectrum and many details differ significantly from previous works. While this low-energy flux is not measurable with present-day technology, it could become a significant background for future direct searches for keV-mass sterile neutrino dark matter.

Comments: 32 pages, 23 figures. Added several references, a new figure and minor changes to match published version