Neutrino-antineutrino interchange of chiral scattering weights
= Neutrino-antineutrino interchange of chiral scattering weights
Crossing a massless neutrino to an antineutrino reverses the antisymmetric part of its <spin tensor>. The $s^2$ and $u^2$ weights exchange, giving $\sigma_{\bar\nu}=G_F^2s[(c_V-c_A)^2+(c_V+c_A)^2/3]/(4\pi)$ for the same <electron> couplings. This is a low-energy contact statement rather than a replacement for a full weak-boson propagator.