High energy photon-neutrino interactions

A general decomposition of the amplitudes for the $2\to 2$ processes $\gamma\nu\to\gamma\nu$ and $\gamma\gamma\to\nu\bar{\nu}$ is obtained using gauge invariance and Bose symmetry. The restrictions implied by this decomposition are investigated for the reaction $\gamma\gamma\to\nu\bar{\nu}$ by computing the one-loop helicity amplitudes in the standard model. In the center of mass, where $\sqrt{s} = 2\omega$, the cross section grows roughly as $\omega^6$ up to the threshold for $W$-boson production, $\sqrt{s} = 2m_W$. Astrophysical implications of very high energy photon-neutrino interactions are discussed.