New limits on neutrino magnetic moment through nonvanishing 13-mixing

The relatively large value of the neutrino mixing angle ${\ensuremath{\theta}}_{13}$ set by recent measurements allows us to use solar neutrinos to set a limit on the neutrino magnetic moment involving the second and third flavor families, ${\ensuremath{\mu}}_{23}$. The existence of a random magnetic field in the solar convective zone can produce a significant antineutrino flux when a nonvanishing neutrino magnetic moment is assumed. Even if we consider a vanishing neutrino magnetic moment involving the first family, electron antineutrinos are indirectly produced through the mixing between the first and third families and ${\ensuremath{\mu}}_{23}\ensuremath{\ne}0$. Using KamLAND limits on the solar flux of electron antineutrino, we set the limit ${\ensuremath{\mu}}_{23}<0.95\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}{\ensuremath{\mu}}_{B}$ as a reasonable assumption on the behavior of solar magnetic fields. This is the first time that a limit on ${\ensuremath{\mu}}_{23}$ has been established in the literature directly from neutrino interactions with magnetic fields, and, interestingly enough, is comparable with the limits on the neutrino magnetic moment involving the first family and with the ones coming from modifications to the electroweak cross section.