Helicity-flipping neutral currents andγγ→νν¯

The process $\gamma \gamma \to ({\pi }^0 or \eta )\to \nu \overline{\nu }$, which can be induced by helicity-flipping scalar and/or pseudoscalar neutral currents, may be of significance in various astrophysical processes. For temperatures of order ${10}^{11}$ °K, the conversion rate into neutrinos via this mechanism is enormous, thus suggesting that this process may be important in the understanding of the early universe and of supernovas.