  The next generation of solar neutrino detectors will provide a precision
measure of the $^8$B electron-neutrino spectrum in the energy range from 1-15
MeV. Although the neutrino spectrum emitted by $^8$B $\beta$-decay reactions in
the Sun's core is identical to the neutrino spectrum measured in the
laboratory, due to vacuum and matter flavor oscillations, this spectrum will be
very different from that measured on Earth by the different solar neutrino
experiments. We study how the presence of dark matter (DM) in the Sun's core
changes the shape of the $^8$B electron-neutrino spectrum. These modifications
are caused by local variations of the electronic density and the $^8$B neutrino
source, induced by local changes of the temperature, density and chemical
composition. Particularly relevant are the shape changes at low and medium
energy range $(E_\nu\le 10 {\; \rm MeV})$, for which the experimental noise
level is expected to be quite small. If such a distortion in the $^8$B$\nu_e$
spectrum were to be observed, this would strongly hint in favor of the
existence of DM in the Sun's core. The $^8$B electron-neutrino spectrum
provides a complementary method to helioseismology and total neutrino fluxes
for constraining the DM properties. In particular, we study the impact of light
asymmetric DM on solar neutrino spectra. Accurate neutrino spectra measurements
could help to determine whether light asymmetric DM exists in the Sun's core,
since it has been recently advocated that this type of DM might resolve the
solar abundance problem.
