Two-photon decay
= Two-photon decay
{title2=$E_\gamma^*=Mc^2/2$}
Decay of a massive parent into exactly two <photons>. In its rest frame, <momentum conservation> requires opposite photon momenta of equal magnitude, so each photon has energy $Mc^2/2$. A boost along their common axis gives laboratory photon energies $\gamma Mc^2(1\pm\beta)/2$. Their product stays $(Mc^2/2)^2$ in that collinear configuration; other emission angles require the corresponding angular <Lorentz transformation>.