Relic Neutrino Helicity Evolution in Galactic Magnetic Field and Its Implications

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 pioneering work of Baym and Peng. We find that with magnetic moments consistent with experimental bounds and even several orders of magnitude smaller, the helicity of relic neutrinos rotates with a substantial directional anisotropy. Averaged over directions this would simply reduce the apparent flux; if the direction of the incident neutrino could be measured, the directional anisotropy in the interaction probability could become a powerful diagnostic. We study the effects of $\nu$ spin rotation on C$\nu$B detection through the inverse tritium decay process.