Implications of a nonzero neutrino mass for the processγγ→νν¯

Recent considerations relating to neutrino oscillations and to the decay $\mu \to e\gamma$ suggest that neutrinos may acquire a small but nonzero mass. The process $\gamma \gamma \to {\pi }^0\to \nu \overline{\nu }$ could then proceed via either an induced $S$,$P$ coupling arising from a primitive $V$,$A$ neutrino current or via a fundamental $S$,$P$ neutrino coupling. Although the resulting $\gamma \gamma \to {\pi }^0\to \nu \overline{\nu }$ cross section would, in the former case, be suppressed by a factor of order ${\left(\frac{m_{\nu }}{m_{\pi }}\right)}^2$, this process could, nonetheless, be of interest in astrophysical processes in a temperature region where the pion pole is significant.