Formula_22978

\[b_{\varphi_{1} \varphi_{2}}=\int_{\mathbb{R}^{v}} \int_{\mathbb{R}^{v}} \varphi_{1}\left(x_{1}\right)\left(-\Delta+m^{2}\right)\left(x_{1}, x_{2}\right) \varphi_{2}\left(x_{2}\right) d x_{1} d x_{2} ;\]