We have searched for exotic neutrino-electron interactions that could be
produced by a neutrino millicharge, by a neutrino magnetic moment, or by dark
photons using solar neutrinos in the XMASS-I liquid xenon detector. We observed
no significant signals in 711 days of data. We obtain an upper limit for
neutrino millicharge of 5.4×10−12e at 90\% confidence level
assuming all three species of neutrino have common millicharge. We also set
flavor dependent limits assuming the respective neutrino flavor is the only one
carrying a millicharge, 7.3×10−12e for νe, 1.1×10−11e for νμ, and 1.1×10−11e for ντ.
These limits are the most stringent yet obtained from direct measurements. We
also obtain an upper limit for the neutrino magnetic moment of
1.8×10−10 Bohr magnetons. In addition, we obtain upper limits for
the coupling constant of dark photons in the U(1)B−L model of
1.3×10−6 if the dark photon mass is 1×10−3 MeV/c2,
and 8.8×10−5 if it is 10 MeV/c2