We discuss the limits on the neutrino magnetic moment and hypothetical
interactions with a hidden unparticle sector, coming from the first neutrino
data release of the Borexino experiment. The observed spectrum in Borexino
depends weakly on the solar model used in the analysis, since most of the
signal comes from the mono-energetic 7Be neutrinos. This fact allows us to
calibrate the nu-e scattering cross section through the spectral shape. In this
way, we have derived a limit on the magnetic moment for the neutrinos coming
from the Sun (in which a nu_mu and nu_tau component is present): mu_nu<8.4E-11
mu_B (90%CL) which is comparable with those obtained from low energy reactor
experiments. Moreover, we improve the previous upper limit on magnetic moment
of the nu_tau by three orders of magnitude and the limit on the coupling
constant of the neutrino with a hidden unparticle sector.Comment: 16 pages, 3 figures. Some clarifications and references added.
Accepted for publication in Phys. Rev.
