Formula_26052

\[\begin{gathered}\left\langle\xi\left(\varphi_{1}\right), \xi\left(\varphi_{2}\right)\right\rangle=\left(\left(-\Delta+m^{2}\right)^{-1} \varphi_{1}, \varphi_{2}\right)_{L_{2}\left(\mathbb{R}^{2}\right)}= \\=\int_{\mathbb{R}^{2}} \frac{\tilde{\varphi}_{1}(k) \overline{\tilde{\varphi}_{2}(k)} d^{2} k}{k^{2}+m^{2}},\end{gathered}\]