Formula_2993

\[\begin{gathered}\varphi(x)=(2 \pi)^{-3 / 2} \int d p\left(2 p^{0}\right)^{-1 / 2}\left\{e^{i p x} a^{+}(p)+e^{-i p x} a^{-}(p)\right\}, \\p^{0}=\left(p^{2}+m^{2}\right)^{1 / 2},\end{gathered}\]