Formula_21180

\[(\operatorname{Re} \mathscr{E}) \eta^{\mu v}\left(\partial_{\mu}+\frac{\alpha_{\mu}}{\alpha}\right) \partial_{v} \mathscr{E}-\eta^{\mu v} \partial_{\mu} \mathscr{E} \partial_{v} \mathscr{E}=0,\]