Speaker
Description
We simulate the evolution of the helicity of relic neutrinos as they propagate to Earth
through a realistic model of the Galactic magnetic field, improving upon the rough estimates in
the literature. For magnetic moments consistent with experimental bounds and several orders of
magnitude smaller, we confirm that the helicity of relic neutrinos and anti-neutrinos rotates so
much that the spin projection changes by O(1). However, as we show, the total event rate in an
inverse tritium beta decay (ITBD) experiment changes by less than a few percent, unless the lightest
neutrino has mass of order 0.001 eV or less. Such a tiny reduction in the absolute rate relative to
the standard model value would be very difficult to establish, even if detecting relic neutrinos were
routine. However as we show, the directional anisotropy of the rate in a polarized ITBD detector
is O(10%) as long as the lightest neutrino mass is O(0.01 eV). Thus with percent-level error bars
on the absolute neutrino flux and its directional anisotropy, both the mass and magnetic moment
of the relic neutrinos can in principle be probed if they are within a few orders of magnitude of
current bounds.
