  We develop a first-principles formalism to compute the distortion to the
relic neutrino density field caused by the peculiar motions of large-scale
structures. This distortion slows halos down due to dynamical friction, causes
a local anisotropy in the neutrino-CDM cross-correlation, and reduces the
global cross-correlation between neutrinos and CDM. The local anisotropy in the
neutrino-CDM cross-spectrum is imprinted in the three point cross-correlations
of matter and galaxies, or the bispectrum in Fourier space, producing a signal
peaking at squeezed triangle configurations. This bispectrum signature of
neutrino masses is not limited by cosmic variance or potential inaccuracies in
the modeling of complicated nonlinear and galaxy formation physics, and it is
not degenerate with the optical depth to reionization. We show that future
surveys have the potential to detect the distortion bispectrum.
