Shapes of solar-neutrino spectra: Unconventional tests of the standard electroweak model

The shapes of the neutrino energy spectra produced by β decays or by nuclear reactions in the solar interior are compared to the corresponding spectral shapes that are produced in a terrestrial laboratory. The most important effects of the Sun, caused by thermal motion of the neutrino-emitting nuclei and by gravitational redshifts, are shown to be small. Any currently measurable difference between the observed shape of a solar-neutrino energy spectrum and the spectrum shape for a terrestrial neutrino source must be due to a departure from the standard electroweak model.